Photo of the Day

Rainbow Over Stony Creek Valley
Late this afternoon, this rainbow accompanied passage of a brief rain shower over the Stony Creek Valley and Saint Anthony’s Wilderness near Rausch’s Gap in Lebanon County, Pennsylvania.

Photo of the Day

Eastern Chipmunk
There’s now a sense of urgency because for the Eastern Chipmunk, the opportunities to gather and store nuts, seeds, and acorns are slipping away.  The time has arrived for retreat to its burrow where, because it stores no body fat for winter, this member of the squirrel family (Sciuridae) relies upon its cache of provisions for snacking between periods of extended slumber during the coldest months of the year.

Five Favorite Visitors from the Northern Forests

As the autumn bird migration draws to a close for 2024, we’re delighted to be finding five of our favorite visitors from the coniferous and mixed forests of Canada and the northernmost continental United States.

Male Yellow-bellied Sapsucker
Yellow-bellied Sapsuckers drill evenly spaced holes which they repeatedly visit to harvest “sap” and the insects that become trapped therein.  These surgically small excavations penetrate only the bark and the phloem, a shallow, spongy layer of the trunk that carries sugars from the leaves to other parts of the tree.  Seldom do they puncture the thin, underlying cambium layer which protects the true sapwood.  After healing, sapsucker holes leave linear rows of small scars which are sometimes still discernible decades after a bird’s final visit.  This adult male will probably linger in the Lower Susquehanna River Watershed until colder weather renders the tree totally dormant, the flow of “sap” ebbs, and small insects become harder to find.  Then he’ll make his way off toward southern forests of oak and pine for the remainder of the winter.  Sapsuckers work their way north as sugary “sap” begins flowing again in the spring.
Hermit Thrush
The Hermit Thrush is another denizen of coniferous and mixed forests.  In habitats with dense cover and sufficient food sources like fruit-bearing shrubs and vines, some will remain through the winter.  The Hermit Thrush is the only spot-breasted thrush regularly seen in our region from November through March.
Fox Sparrow
Almost the size of a thrush, the largest of our native sparrows, the Fox Sparrow, is currently at the peak of its southbound migration.  While taking a break from their nocturnal flights, some may stray from forest edges to visit suburban feeding stations.  Most leave our area by mid-December, then begin returning north as early as mid-February.
Pine Siskins
Not present every year, flocks of Pine Siskins are beginning to arrive in the lower Susquehanna region.  They are currently most common along the mountain tops of the Ridge and Valley Province where they are feeding on the seeds of the Sweet Birch, a tree also known as Black Birch.  Look for them around niger seed feeders and on the prickly seed balls of cultivated American Sweetgum, but don’t be surprised if they quickly pass us by to spend the winter on the Atlantic Coastal Plain to our south where this native tree grows in abundance.
Female/Juvenile Male Purple Finch
Since late October, Purple Finches have been widespread throughout the region.  These female/juvenile male types are frequently being seen at feeders, particularly near woodlands and other areas with stands of conifers.
Male Purple Finch
Less frequently seen are the adult male Purple Finches in their raspberry-colored plumage.  What a dandy.

While right now is the best time to get out and look for these species from the northern forests, any or all of them could linger into the winter months, particularly where the food supply is sufficient and conifers and other evergreens provide cover from the blustery weather.

Another Unusual Golden Eagle?

Golden Eagle and Common Raven
This Golden Eagle was seen tangling with a Common Raven as it passed a lower Susquehanna valley hawk-counting station earlier today.
Golden Eagle and Common Raven
The two traded barbs until continuing down the ridge to the southwest.
Unusual Golden Eagle?
A composite image shows a close-up view of the migrating raptor.  It has the showy white tail with a black terminal band that Golden Eagle enthusiasts regard as particularly spectacular on these majestic birds when they’re young.  But where are the conspicuous white patches in the wings?  And just how old is this eagle?  We’ll give you a hint; if you note the appropriate field marks, this is actually a classic example of a bird its age.  To learn the critical field marks and to determine the age of this bird, be certain to click the “Golden Eagle Aging Chart” tab at the top of this page.

Yet Another “Barthelemyi Golden Eagle” at Second Mountain Hawk Watch

Earlier today, observers at Second Mountain Hawk Watch at Fort Indiantown Gap in Lebanon County, Pennsylvania, were treated to excellent looks at a migrating “Bartelemyi Golden Eagle”, a rare variant of the species recognized by white scapulars that mimic a pair of epaulets on the shoulders.

"Barthelemyi Golden Eagle"
The “Barthelemyi Golden Eagle” variant is recognized by the pair of white scapulars that create epaulets on its shoulders.  Molt in the primaries indicates that this is a second-year (Basic I) bird.
"Barthelemyi Golden Eagle"
This is the third “Barthelemyi Golden Eagle” sighting in the past eight years at Second Mountain.  The first was on October 21, 2017, and the second was less than a year ago on December 6, 2023.

For more information on the “Barthelemyi Golden Eagle” sightings at Second Mountain, see our post from December 6, 2023.

Remember, it ain’t over ’til it’s over, there are still more eagles and other raptors on the way!  And if you’d like to catch a glimpse of one of these rare “Barthelemyi Golden Eagles”…well, you know where you oughta be.

A Visit to Hawk Mountain Sanctuary

Mid-November is our favorite time of year to visit Hawk Mountain Sanctuary on Blue Mountain/Kittatinny Ridge just to the east of the lower Susuquehanna valley near Kempton, Pennsylvania.  By now, the huge crowds that come to see October’s world-famous raptor flights and spectacular fall foliage have dwindled to small groups of serious hawkwatchers and hardy trail enthusiasts.  Join us as we drop in on the Keystone State’s most famous birding destination.

Hawk Mountain Sanctuary Entrance
The entrance to Hawk Mountain Sanctuary is located at 1700 Hawk Mountain Road off PA Route 895 east of PA Route 61.
Hawk Mountain Sanctuary Headquarters
Start your visit with a stop inside the refuge headquarters building where you’ll find raptor ecology and migration displays, a gift shop, and a window overlooking a busy bird-feeding station.  Hawk Mountain is a non-profit organization that receives no taxpayer support and relies largely upon membership fees and donations for the majority of its operating expenses.  Inside the headquarters building, you can pay dues and join on the spot.
Native Plant Garden
The native plant habitat includes a pond and a rain garden that collects stormwater from the roof of the headquarters building.  There’s also a memorial fern garden named for the refuge’s first curator, Maurice Broun, author of a 1938 index to the ferns of North America.
Trail Sign
After a visit to the habitat garden, it’s time to make our way toward the lookouts.
PA Historical Marker, Hawk Mountain Sanctuary.
2024 marks the 90th anniversary of the founding of Hawk Mountain Sanctuary.  We stopped at the trail crossing along the mountain road to admire this newly erected sign.
Hawk Mounatin Sanctuary Trailhead Gate
Trail fees are collected to support the sanctuary’s operations and maintain its 2,600 acres.  Members enter free.
Hawk Mountain Interpretive Kiosk
Interpretive signs and trail information are provided throughout the refuge, particularly along the mile-long climb to the North Lookout.
River of Rocks Trail
Aside from the route to the lookouts (along which sturdy shoes and good balance are a must), many of the sanctuary’s hiking trails require special equipment and preparations.  Be certain to follow the posted guidelines.
Raptor education panels along the lookout trail.
The scope of Hawk Mountain’s educational mission includes topics ranging from local Appalachian natural history to global raptor conservation.
Hawk Mountain South Lookout
Just a few hundred yards from the entrance gate, South Lookout provides a panoramic view of the “River of Rocks” talus outcrop and beyond.  On days with southerly winds, autumn raptor flights are sometimes enumerated from this location.
North Lookout
Hawk Mountain’s “classroom in the sky”, the North Lookout, hosts school and scout groups learning raptor identification and ecology.  It’s the sanctuary’s primary location for counting thousands of migrating birds of prey each fall.
Turkey Vulture
Students quickly learn to identify distant Turkey Vultures by their upturned wings held in a dihedral posture and by their rocking motion in flight.
Hawk Mountain North Lookout
After the pupils depart for the day, there are but few observers remaining to find and count passing hawks and eagles during mid-November.
Southern Red-backed Vole
While sitting quietly among the boulders of North Lookout waiting for the next bird to come along, one can be treated to a visit by one or more of a local population of Southern Red-backed Voles (Clethrionomys gapperi).
Red-tailed Hawk
Red-tailed Hawks remain common among the flights of mid-November migrants.
Red-tailed Hawk
And it happens to be an ideal time to see Red-shouldered Hawks on the move.
While you were busy looking up, the Southern Red-backed Vole was at your feet scarfing up the crumbs from your sandwich.  When not availed of our leftovers, its diet includes seeds, various plant parts, and subterranean fungi.
Common Ravens
Playful groups of Common Ravens often provide comic relief during interludes in the parade of migrants.
Northern Short-tailed Shrew
Don’t look now, but your friend the vole has scurried away and a Northern Short-tailed Shrew (Blarina brevicauda) has arrived from beneath the rocks to finish the remnants of your lunch.  On the rocky outcrops atop the ridges of southeastern Pennsylvania, these mammals are often found in close company; Red-backed Voles traveling through the burrows and runways created by Northern Short-tailed Shrews instead of excavating their own.  Unlike the vegetarian voles, shrews are classified as insectivores, behaving mostly as carnivorous mammals.  Equipped with salivary venom, they can consume prey as large as other similarly sized vertebrates, including small voles.
Bald Eagle
Flights of Bald Eagles thrill visitors on North Lookout throughout November.
Golden Eagle
But late-season visitors really want to see a Golden Eagle.  On a chilly day with gusty northwest winds, few are disappointed.
Hatch-year/juvenile American Goshawk
We got very lucky during a recent day on North Lookout, spotting this rarity, a hatch-year/juvenile American Goshawk (Accipiter atricapillus), a species which, in 2023, was split from the Northern Goshawk (Accipiter gentilis), a species which was simultaneously assigned the new common name Eurasian Goshawk.  Even more recently, within the past several weeks, the genus name Astur has replaced Accipiter for the goshawks, now formally known as the the American Goshawk (Astur atricapillus) and the Eurasian Goshawk (Astur gentilis).  The new classification includes Cooper’s Hawk in the genus Astur, while the Sharp-shinned Hawk remains in the genus Accipiter.
Hatch-year/Juvenile American Goshawk
A November specialty, a hatch-year/juvenile American Goshawk (Astur atricapillus) passes the North Lookout.  During this century, the drop in American Goshawk numbers has been precipitous.  Most eastern hawk-counting stations see fewer than four or five goshawks during their entire fall season.  Many no longer see them at all.
Hatch-year/juvenile American Goshawk
Here and gone in a jiffy, a brief but memorable look at a hatch-year/juvenile American Goshawk.

If the cold of mid-November doesn’t cramp your style, and if you’d like to seize your best opportunity for a much-coveted sighting of one or more of the late-season specialties, then now is the time to visit Hawk Mountain Sanctuary.  Bring a cushion upon which to sit, dress in layers, pack a lunch, and plan to spend the day.  You could be rewarded with memorable views of the seldom-encountered species some people spend years of their lives hoping to see.

To learn more, check out the Hawk Mountain Sanctuary website.

Photo of the Day

With low relative humidity, gusty daytime breezes, and little or no rain in the forecast, many counties and local municipalities in the lower Susquehanna basin have enacted bans on open burning to prevent accidental wildfires.  With these dangerous conditions prevailing, you know enough not to burn trash and leaves, or to carelessly discard ashes or smoking materials.  And you’re smart enough to keep close watch on fires used for cooking and to keep them within approved enclosures such as a grill with a lid.  But have you thought of eliminating another common form of ignition, this one originating from your car or truck?  Your motor vehicle’s catalytic converter is hot enough to ignite dry leaves, grasses, and crop residues like corn shocks upon contact, so be extra careful where you park.  Be certain that your pollution control device remains free and clear of combustibles!

Photo of the Day

During the summer, the Lesser Angle-winged Katydid has little difficulty hiding among the lush green foliage of hardwood trees.  Oft times, the only sign of its presence is its call, a series of short rapid rattles, “ttt—-tttt—-ttt”, issued with a second or two of silence between each rattle.  The call is often part of the nocturnal chorus it shares with other species of katydids on warm evenings.  Frost and freeze usually bring these annual breeding rituals to end.  But during our current resurgence of warm autumn weather, we found this hardy survivor in a forest clearing where it has little hope of escaping notice among bare trees and earth-tone fallen leaves.  As the afternoon temperature soared into the upper seventies, it further revealed its presence by striking up its tell-tale mating call, “ttt—-tttt—-ttt.”

Eagle Time on the Ridges and River

As we enter November, migratory raptor flights through the Lower Susquehanna River Watershed transition to the bigger birds.  Whether you’re on the river, on a mountain, or just outside your humble abode, persistent alertness to soaring avians can yield rewarding views of a number of late-season specialties.

Red-tailed Hawk
Red-tailed Hawks dominate the southbound raptor flights in November.
Juvenile Red-tailed Hawk
Juvenile (hatch-year) Red-tailed Hawks are generally less wary and more inquisitive than the more experienced adult birds.  Their curiosity frequently gets them into trouble, particularly when they try to hunt small rodents in traffic along busy roadways.
Adult Red-shouldered Hawk
Far fewer in number are migratory Red-shouldered Hawks.  In our region, these denizens of bottomland forests more commonly migrate along the southern edge of the Piedmont and through the upper Atlantic Coastal Plain.
A hatch-year (juvenile) Red-shouldered Hawk
A southbound hatch-year (juvenile) Red-shouldered Hawk.
Peregrine Falcon
Mixed-race Peregrine Falcons, the descendants of birds reintroduced into the Mid-Atlantic States during the late twentieth century, often roam our region during the late-fall and winter months before settling into their nesting territories with the approach of spring.  We spotted this one along a local ridge, but you may be more likely to see them in the city or near a bridge or dam on the river.
Peregrine Falcon
As this adult peregrine passed the lookout, we noted its full crop.  A sign it just completed a successful hunt.

A visit to a ridgetop on a breezy day—particularly after passage of a cold front—may give you the chance to see numerous eagles as well.

A second-year (Basic I) Bald Eagle rolls over while pursuing an adult Bald Eagle.
A second-year (Basic I) Bald Eagle barrel rolls while pursuing an adult Bald Eagle.

This afternoon, we got lucky and were treated to a bit of an aging clinic presented by the Bald Eagles we observed and photographed.  Careful determination of the age classes of raptors counted by hawkwatchers can provide an early warning of problems in the ecosystems that support populations of these top-of-the-food-chain predators.  For example: during the 1950s and early 1960s, a progressively lower percentage of juvenile and other non-adult age classes among the Bald Eagles being observed forewarned of the dangers of dichlorodiphenyltrichloroethane (DDT) pesticide in the environment.  The principle effect of accumulations of the DDT toxins in eagles, Ospreys, Peregrine Falcons, and other predatory birds that consumed waterfowl and/or fish was to thin their eggs shells.  The result was widespread brood failure and a near total loss of new generations of offspring.  Eventually, nearly all Bald Eagles being seen in areas impacted by DDT were progressively older adults, most of which failed as nesting pairs.  As the adult birds began dying off, the Bald Eagle population dwindled to numbers that raised fears of the species’ extinction.  Implementation of the DDT cancellation order and the Clean Water Act in 1972, and the Endangered Species Act in 1973, helped save the Bald Eagle.  But our regional “Eastern Peregrine Falcon”, a bird with a shorter life span than the Bald Eagle, was unable to endure the years of DDT use, dioxin pollution, and illegal hunting and egg collecting.  Its population is gone.

Hatch-year Bald Eagle
A hatch-year (juvenile) Bald Eagle is typically dark headed and in a fresh set of juvenile flight feathers that exhibit no signs of molt.  If the reproduction season and the months that followed were favorable for this year’s brood of new eagles, there should be nearly as many hatch-year birds as there are adults in an overall population.
Second-year Bald Eagle
By November, second-year (Basic I) Bald Eagles are replacing many of their flight feathers and often show ragged trailing edges in the wings due to the retention of some of the well-worn and notably longer juvenile feathers.  Varying amounts of white mottling are visible on the breast, belly, and underwing coverts.  Due to mortality, there are usually fewer second-year Bald Eagles than there are hatch-year or adult birds.
Second-year (Basic I) Bald Eagle.
Another example of a second-year (Basic I) Bald Eagle.
Third-year Bald Eagle
Third-year (Basic II) Bald Eagles show more yellow in the bill and an “osprey face”, a white head with a wide dark line through the eye.  Most of the juvenile flight feathers have been replaced, so the wing edges appear more uniform.  Like the second-year eagles, there is a varying amount of white in the breast, belly, and underwing coverts.  In an overall population of eagles, birds in this age class are usually less common than those that are younger or those that are adults.
Bald Eagle Age Classes: First Three Years
Composite image of Bald Eagles in typical November plumage during their first three years.  To see more images like this, be certain to click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab at the top of this page.
Fourth-year Bald Eagle
A fourth year (Basic III) Bald Eagle will often be seen with a black-bordered tail and a thin dark line through the eye.  In some birds, traces of these traits can linger into the fifth year and beyond.  These plumage types are usually the least frequently observed among an overall population of Bald Eagles.  (Note:  In these older birds, there develops significant variation in the timing of feather molt.  In rare cases, fourth-year Bald Eagles may show minimal dark color in the tail or eye line and may appear to be in near definitive adult plumage.)
A possible fifth-year (Basic IV) Bald Eagle.
A possible fifth-year (Basic IV) Bald Eagle.
Adult Bald Eagles in definitive plumage. 
Adult Bald Eagles in definitive plumage.  Birds in this plumage class are often the most frequently observed because the group includes all eagles five or six years of age and older.

While the Bald Eagles are still stealing the show, cold and gusty weather should bring an increasing number of Golden Eagles our way during the remainder of the month.  Some are already trickling through…

A "before-third-year" Golden Eagle.
This “before-third-year” Golden Eagle shows no visible signs of molt in its juvenile (hatch-year) plumage, but a look at the upperwing coverts is needed to properly age the bird.  To learn more about the molt sequence in Golden Eagles, be sure to click the “Golden Eagle Aging Chart” tab at the top of this page.
A "before-third-year" Golden Eagle passing the lookout along with a second-year Bald Eagle.
A “before-third-year” Golden Eagle (top) passing the lookout along with a second-year Bald Eagle (bottom).
"Before-third-year" Golden Eagle.
Another “before-third-year” Golden Eagle.  More are on the way!

Later this month, Bald Eagle numbers on the lower Susquehanna below Conowingo Dam (U.S. 1) near Rising Sun, Maryland, will begin to grow.  Fisherman’s Park, located along the west shoreline below the dam, is an excellent place to observe and photograph scores of these regal birds.  And few places provide a better opportunity to learn to differentiate Bald Eagle age classes.  If you’re really lucky, a Golden Eagle or two may drop in as well.  So plan to make the trip.  The best time to visit is on a weekday.  The parking lot can become overcrowded on weekends and will be closed under such circumstances.  It’s best to avoid the long Thanksgiving weekend as well.

Migrating Adult Bald Eagles
Remember to always look up.

Three’s Company

For many species of terrestrial vertebrates living in the lower Susquehanna valley, it’s time to take refuge in a safe place below ground to enter a winter-long slumber.  The numerous frosty nights of the past two weeks have expedited the stragglers’ efforts to find a suitable place to pass our coldest months.

Wood Turtles
Aside from the Eastern Box Turtle (Terrapene carolina carolina), the Wood Turtle (Glyptemys insculpta) is our most terrestrial species of testudine, however it is seldom found far from wet bottomlands.  Last week, we found this pair preparing to burrow into alluvial soils along the edge of a floodplain wetland where they will spend the winter.  In recent years, Wood Turtle numbers have plummeted due to habitat fragmentation and loss, and due to collecting by short-sighted petkeepers and profiteers.
Wood Turtle
A sluggish Wood Turtle catching a few last rays of sunshine before digging in for the winter.   If you encounter these or any turtles now or at any time of year, it’s important that they not be disturbed.  Look and leave them be.

And now, just in time for Halloween, a look at some hibernating species that some of our more squeamish readers consider to be “scary”.

In the mountainous forests of the Ridge and Valley Province, there lives a seldom seen little mouse which, unlike the more familiar species found in the fields, farms, and homes of our valleys and Piedmont, spends almost half the year in true hibernation.

Woodland Jumping Mouse
The Woodland Jumping Mouse (Napaeozapus insignis) is a nocturnal species of rodent found primarily on rocky forest slopes, particularly those with growths of Eastern White Pine and Eastern Hemlock.  Unlike the similar White-footed Mouse, a species that sometimes enters homes in the fall and remains active year-round, the Woodland Jumping Mouse builds a small subterranean nest among rocks and boulders where it will enter a long winter slumber, often not emerging until the milder days of April.  During the long hibernation, these mice sometimes fatally diminish the energy stored in their body fat; up to 75% may perish before spring arrives (Merritt, 1987).

In spring and fall, Eastern (Black) Ratsnakes are frequently seen basking in the sun as they absorb heat and get their metabolism going.  During the hottest days of summer, when ambient air temperature is sufficient for their needs, they become nocturnal, hunting mice and other creatures that are also active at night.  During October, they make their way back to a winter den where they will remain until March or April.

Eastern Ratsnake
A last-minute Eastern (Black) Ratsnake makes a slow late-October trek across a mountain road toward a winter den on the south slope of the ridge.
Eastern Ratsnake
This Eastern Ratsnake is on its way to a cold-season hideout where it may spend the darker months in the company of other communal hibernators including…
Eastern Copperhead
…Eastern Copperheads…
Timber Rattlesnake
…and Timber Rattlesnakes.

That’s right, all three of these snakes are known to cohabitate, not just during hibernation, but at other times of the year as well.  And you thought they were mean and nasty to anything and everything in their path, didn’t you?

Here in the northeastern United States, fear of indigenous wild snakes is a totally irrational anxiety.  It’s a figment of our indoctrination.  Their wicked reputation is almost exclusively the result of a never-ending stream of demonizing propaganda from the pulpit, press, parents, panicked, and picture shows.  All they want from you and I is to be left alone.  Want something to really be afraid of this Halloween?  Try domestic dogs.  That’s right—the “friendly” pooch.  In the United States, they’ll land hundreds of people in the emergency room today.  Don’t like that one.  How ’bout cars and trucks.  They’ll kill and maim people all day long.  And don’t forget about sugar.  Yes friends, that sweet treat is pure poison that kills all day long.  Happy Halloween!

  SOURCES

Merritt, Joseph F.  1987.  Guide to the Mammals of Pennsylvania.  University of Pittsburgh Press.  Pittsburgh, PA.  pp.230-233.

Shaffer, Larry L.  1991.  Pennsylvania Amphibians and Reptiles.  Pennsylvania Fish Commission.  Harrisburg, PA.

A Towering American Elm

During the past week, Uncle Tyler Dyer has been out searching for autumn leaves to add to his collection.  One of the species he had not encountered in previous outings was the American Elm (Ulmus americana), so he made a special trip to see a rare mammoth specimen in a small neighborhood park (Park Place) along Chestnut Street between 5th and Quince Streets in Lebanon, Pennsylvania.

American Elm at Park Place in Lebanon, Pennsylvania
Possibly the largest and oldest remaining American Elm in the lower Susquehanna watershed, the Park Place tree in Lebanon exceeds 60 feet in height and may be more than 300 years of age.  In the nearly one hundred years since Dutch elm disease (DED) first began killing elms in eastern North America, this tree has been spared the fatal effects of the infection.  DED is caused by several species of microfungi (Ophiostoma ulmi, O. himal-ulmi, and O. novo-ulmi) spread by numerous bark beetle (Curculionidae) species.  As early as 1928, infected beetles arrived in the United States from the Netherlands among shipments of logs.
Leaves of the American Elm.
Leaves of the American Elm.

There’s still time to get out and see autumn foliage.  With warmer weather upon us—at least temporarily—it’s a good time to go for a stroll.  Who knows, you might find some spectacular leaves like these collected by Uncle Ty earlier this week.  All were found adorning native plants!

Winged Sumac
Winged Sumac (Rhus copallina), a small native tree.  In case you’re wondering, it’s not poisonous.
Black Chokeberry
Black Chokeberry (Photinia melanocarpa), a native shrub also known as Aronia.  It produces black-colored fruits in summer.
Red-osier Dogwood
Red-osier Dogwood (Cornus sericea), a shrub that prefers wet or damp soils.  It yields white fruits.
Maple-leafed Viburnum
Maple-leafed Viburnum (Viburnum acerifolium), a native shrub of upland forest understories.
Highbush Blueberry
Highbush Blueberry (Vaccinium corymbosum), a native shrub and the source of many cultivated forms of the popular fruit.
To identify your finds, be certain to click the “Trees, Shrubs, and Woody Vines” tab at the top of this page to check out Uncle Ty’s extensive collection.

Photo of the Day

Winter Wren
Another arrival from the northern forests, the petite Winter Wren is often difficult to observe.  Look for it right now in wetlands, along wooded streams, and among fallen timber where it sometimes resembles a mouse scurrying about looking for food.  In good habitat, some of these migrants will remain through the colder months and will on occasion burst into song.  Hearing it is sure to brighten your day.

Photo of the Day

Brown Creeper
Going almost undetected, the Brown Creeper quietly probes the bark for spiders and tiny insects, as well as their eggs, larvae, and pupae.  These unique little birds are rare breeders in the lower Susquehanna valley, finding larger tracts of forest to our north more to their liking.  Now is perhaps the best time of year to find them, while their southbound migration reaches its peak.  Small numbers of Brown Creepers stick around through winter, somehow finding enough to eat among the cracks and crevices of the tree trunks.

Things to See While You’re Leaf Peeping

During your foray to view the colorful foliage of the autumn landscape, a little effort will reveal much more than meets the eye of the casual observer.

Fallen Foliage in the Forest
Don’t just stand there like a bump on a log, go for a stroll, watch your step, and have a look around.  There’s a lot to see out there!
Witch-hazel
The dense understory of this forest on Blue Mountain consists almost exclusively of Witch-hazel (Hamamelis virginiana).
Witch-hazel in Flower
Witch-hazel is unique among our native flowering shrubs; it blooms in autumn.
Common Buckeye
Until we experience a heavy frost, some of our most beautiful butterflies, including this Common Buckeye, remain active along forest edges.
An Eastern Tailed Blue
An Eastern Tailed Blue.
A Pearl Crescent.
A Pearl Crescent.
A Variegated Fritillary.
A Variegated Fritillary.
Painted Lady.
A Painted Lady.
Yellow-rumped Warbler
The arrival of large numbers of Yellow-rumped Warblers heralds the transition to movements of migrants that will spend the colder months in temperate climates like ours instead of continuing on to the tropics.  In winter, small numbers of “yellow-rumps” sometimes linger in the Lower Susquehanna River Watershed, as long as a supply of wild berries is readily available.
Palm Warbler
The Palm Warbler, a persistent “tail wagger”, is another late-season migrant that occasionally spends the winter.  The migration of these drab “Western Palm Warblers” will be followed in coming weeks by the more yellowish “Eastern Palm Warblers” of the eastern third of the species’ breeding range in Canada.
White-throated Sparrow
White-throated Sparrows are southbound and easily observed right now.  Many will remain along our brushy forest edges for winter.
Dark-eyed Junco
Another native sparrow, the familiar Dark-eyed Junco, is now arriving.
Yellow-bellied Sapsuckers
The Yellow-bellied Sapsucker is a secretive migratory woodpecker that is currently moving through the region on its way to southern pine forests for the winter.  Juveniles like this one in the lower right remain close to their parents during migration and continue to beg for food.
Pileated Woodpecker
The Pileated Woodpecker is a resident species in our mature forests and woodlands.  We were showered by “sawdust” as we watched this one dismantling a rotted dead tree while searching for beetle grubs and other invertebrates.
Eastern Bluebird
You may see Eastern Bluebirds year-round in the lower Susquehanna valley, but many are migratory.  A southbound push is currently transiting our area.
Hawk Watching on Blue Mountain at Boyd Big Tree Preserve.
Mix your leaf watching with hawk watching by visiting a ridgetop vista like this one at Boyd Big Tree Preserve Conservation Area on Blue Mountain north of Harrisburg and you can double your pleasure.
Common Raven
In addition to spectacular foliage, you stand a good chance of seeing an inquisitive Common Raven…
Screaming Red-tailed Hawk
…or a migrating Red-tailed Hawk that gives you a good scream as it passes by…
Bald Eagle
…or a majestic Bald Eagle.
Common Ravens
You may even double your fun by seeing two Common Ravens…
Red-tailed Hawks
…or a couple of migrating Red-tailed Hawks…
Bald Eagles
…or a pair of Bald Eagles passing thru.

You too can experience the joys of walking and chewing gum at the same time, so grab your field glasses, your camera, and your jacket, then spend lots of time outdoors this fall.  You can see all of this and much more.

Don’t forget to click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab at the top of this page to help you find a place to see both fall foliage and migrating birds of prey in coming weeks.  And click the “Trees, Shrubs, and Woody Vines” tab to find a photo guide that can help you identify the autumn leaves you encounter during your outings.

Photo of the Day

Ruby-throated Hummingbird
Here today, gone tomorrow.  This Ruby-throated Hummingbird lingered around the numerous tubular flowers in the headquarters garden until near darkness last evening.  It was last seen entering the cover provided by our Eastern Hemlocks where it presumably spent the night.  Bright and early this morning, it made repeated visits to Mexican Cigar and this Bat-faced Cuphea to re-energize before resuming its long voyage to the tropics for winter.  This marks the third consecutive year we’ve been visited by late-season hummingbirds during the first week of October.  All were attracted to our nectar-rich plantings.

A Sunny Day to Get Things Moving Again

At last, the bird migration is picking up where it left off after the third week of September when rain, fog, and gloom arrived for a two week stay in the lower Susquehanna valley.  Now that this persistent meteorological interluder has departed the stage, our stalled avians can resume the autumn spectacle.

Barn Swallow
There are still a few Barn Swallows around.  By October, they’ve usually departed for more southern climes.  Our more common late-season species are the Tree and Northern Rough-winged Swallows, both of which tend to be found close to water and are thus able to still grab flying insects on mornings when the air temperature over land is too cold for their favored prey.  We found this Barn Swallow following the lead of its cool-weather counterparts, hawking up its breakfast over a warm sun-drenched pond.
Eastern Phoebe
While the vast majority of the Neotropical flycatchers are now gone for the year, Eastern Phoebes are currently moving through in large numbers.  Like the late-season swallows, these insectivores are a temperate species with an affinity for habitats near water.
Black-throated Green Warbler
Though getting harder to find, there are still some Neotropical warblers moving through. This Black-throated Green Warbler was strongly outnumbered by the Ruby-crowned Kinglets in a mixed flock of woodland songbirds.
Northern Parula
A Northern Parula in the mixed flock of migrants.
Ruby-crowned Kinglet
One of dozens of Ruby-crowned Kinglets encountered this morning.
Blue Jay
Despite the inclement weather, diurnal flights of southbound Blue Jays have continued throughout the past week.
Blue Jays
Migrating Blue Jays are best seen during the first few hours after sunrise.
Red-bellied Woodpecker
Red-bellied Woodpeckers, after extending their range north through the Susquehanna watershed and beyond during the past century, have now become a regular fall migrant as they withdraw from the northernmost periphery of their breeding grounds.  This individual was photographed while taking a break from its diurnal flight and was one of more than three dozen seen at Second Mountain Hawk Watch on Thursday, October 3.
Osprey
After a significant delay, especially for the Neotropical Broad-winged Hawks, diurnal raptor flights have resumed.  Now is the time to see the widest variety of species, including migrants like this Osprey, at any one of the regional hawk-counting stations.
Sharp-shinned Hawk
Numbers of migrating Sharp-shinned Hawks are now reaching their seasonal peak.  Be certain to check out “Hawkwatchers Helper: Identifying Bald Eagles and Other Diurnal Raptors” by clicking the tab at the top of this page.  There you’ll find a listing of regional lookouts and a photo guide to help you identify the species you see.

Delayed by a Week of Rain

During this foggy, dreary week, if you happened to visit a parcel of land that included even a small patch of brushy growth here in the Lower Susquehanna River Watershed, you likely weren’t alone.  Among the migrating songbirds grounded by the inclement weather were an abundance of these thicket-dwelling warblers—a species aptly named the Common Yellowthroat.

Common Yellowthroat
A Common Yellowthroat, on an extended layover due to flight cancellations imposed by this week’s moisture-laden east winds, peers from the dense cover of a tangle of shrubs and thorny vines.
Common Yellowthroat
As soon as the inclement weather moves out, this adult male Common Yellowthroat and other avian migrants will resume their southbound journey.  Until then, he has plenty of time to scrounge around in the low-growing vegetation for insects and other fare to replenish the energy stores needed for the trip.

Get ready.  The sun will show its glow in just a couple of days and when it does, bottled-up birds are going to make a run for it.  Do plan to get out and have a look later this week.

Photo of the Day

A juvenile Scarlet Tanager
We have at last reached the autumnal equinox, a day when everything is even stephen, equal time both with and without sunlight.  Southbound birds like this juvenile Scarlet Tanager can now freely be called “fall migrants”, even though the majority of tanagers and other Neotropical species departed for warmer climes earlier this month, technically during the summer season.

This Week’s Enormous Diurnal Flights

For the past several weeks, we’ve given you a look at the fallout of Neotropical songbirds on mornings following significant nocturnal flights of southbound migrants.  Now let’s examine the diurnal (daytime) flights that have developed in recent days over parts of the lower Susquehanna basin and adjacent regions.

For those observing diurnal migrants, particularly at raptor-counting stations, the third week of September is prime time for large flights of tropics-bound Broad-winged Hawks.  Winds from easterly directions during this year’s movements kept the greatest concentrations of these birds in the Ridge and Valley Province and upper areas of the Piedmont as they transited our region along a southwesterly heading.  Counts topped 1,000 birds or more on at least one day at each of these lookouts during the past seven days.  Meanwhile at hawk watches along the Piedmont/Atlantic Coastal Plain border, where flights topped 10,000 or more birds on the best days last fall, observers struggled to see 100 Broad-winged Hawks in a single day.

Broad-winged Hawks
Dozens of migrating Broad-winged Hawks during a morning liftoff to the north of Blue Mountain.

Among the challenges counters faced while enumerating migratory Broad-winged Hawks this week was the often clear blue skies, a glaring sun, and the high altitude at which these raptors fly during the mid-day hours.

"Kettling" Broad-winged Hawks
Large numbers of Broad-winged Hawks climbing on a thermal updraft to gain altitude can become increasingly difficult to spot in a clear blue sky.
"Kettling" Broad-winged Hawks
Higher and higher they go until they practically disappear from view.
Broad-winged Hawks
Cloud cover can help make locating really high-flying birds a bit easier, but they can sometimes climb into the lower portion of the cloud and vanish.

Another factor complicating the hawk counters’ tasks this week, particularly west of the Susquehanna River, was the widespread presence of another group of diurnal fliers.

Blue Jay
Was it the migratory Blue Jays that are beginning to move through the area?   No.
Sharp-shinned Hawk
Was it the increasing numbers of Sharp-shinned Hawks and other raptors?  No.
Hawkwatchers Scanning the Skies
So what was it that complicated the hawkwatchers’ efforts to find high-flying Broad-winged Hawks during this week’s flights?
Spotted Lanternfly
Is it a bird?  Is it a plane?  No.  And it’s nobody’s superhero either.  It’s the non-native Spotted Lanternfly and it is now very numerous west of the Susquehanna and common enough to the east to make even experienced observers take a second look while scanning the skies for Broad-winged Hawks and other migrating raptors.  Just how many do raptor counters have to contend with?  Even where these invasive insects have become less populous in the lower Susquehanna valley, hundreds still fill the skies above forest clearings around hawk-counting stations including Waggoner’s Gap, Second Mountain, and Rocky Ridge County Park.
Spotted Lanternflies on Radar
Spotted Lanternfly populations explode with great vigor as they colonize areas with plenty of tender new growth on native, non-native, and cultivated shrubs, trees, and vines.  Earlier this week, National Weather Service Doppler Radar in Pittsburgh, Pennsylvania, captured enormous mid-afternoon flights of Spotted Lanternflies in recently invaded areas of southwestern Pennsylvania and eastern Ohio.  (NOAA/National Weather Service Doppler Radar image)
Spotted Lanternflies on Radar
A base velocity image consisting primarily of Spotted Lanternflies in southwestern Pennsylvania and eastern Ohio.  (NOAA/National Weather Service Doppler Radar image)

As the Broad-winged Hawk migration draws to a close during the coming ten days, the occurrence of the one dozen other migratory diurnal raptors will be on the upswing.  They generally fly at lower altitudes, often relying upon wind updrafts on the ridges for lift instead of high-rising thermal updrafts.  They therefore present better observation opportunities for visitors at hawk watch lookouts and are less frequently confused with high-flying Spotted Lanternflies.

Merlin
A Merlin seen earlier this week migrating through the Lower Susquehanna River Watershed.  The numbers of migrating Merlins and other falcons will peak sometime in coming weeks.

Axanthism Gives Green Frogs the Blues

Among the Green Frogs in the ponds at susquehannawildlife.net headquarters, a specific recessive allele is present among the population of these native amphibians.  On occasions when male and female carriers of this particular recessive allele get together to produce offspring, about one quarter of the progeny will receive a copy of this mutated version of a gene from each parent.  The rare recipient of this pair of recessive alleles that happens to survive the process of hatching from its egg and metamorphosing through the tadpole stage to adulthood will reveal the uncommon appearance of an amphibian with the condition resulting from this inheritance—axanthism.

Axanthic Green Frog
Axanthic Green Frogs and other amphibians do not produce yellow pigment, therefore the normally yellow surfaces of their bodies appear white, the green surfaces blue.  Axanthism is expressed only in individuals possessing a pair of specific recessive alleles for a gene that affects the cells that produce the yellow pigment.  For the trait to be expressed, a frog must receive one copy of the recessive allele from each parent.
Axanthic and Typical Green Frogs
The last axanthic Green Frog we saw in the headquarters ponds was this male (seen here with a typical male Green Frog) found back in July, 2008.  Green Frogs that receive two copies of a dominant allele or a copy of a dominant and a recessive allele from their parents will not express the recessive trait for the axanthism gene.  Making observation of cases of axanthism even rarer is the fact that blue coloration can make these frogs exceptionally susceptible to predation.  Few live long enough to reproduce and thus increase the occurrence of the mutation in a population of frogs*.  This cyanic individual was present during a time when “outdoor” Domestic Cats were killing frogs to take home to their misguided humans.  After this brief sighting and single photograph, this blue Green Frog was never seen again. 

*The incidence of axanthic frogs can increase when a blue parent, which has a pair of the recessive alleles and is therefore said to be homozygous recessive, mates with a typical-looking frog that carries both a dominant and a recessive allele for the axanthism gene and is therefore said to be heterozygous.  Approximately 50% of the young from this pairing will express axanthism.  By comparison, a pair of frogs that are both heterozygous will produce 25% axanthic young, and a pair of frogs that are both blue (homozygous) will yield 100% axanthic young.  A pair of frogs that includes an individual that is herterozygous and a mate that is homozygous dominant for the gene will produce no axanthic frogs, but 50% of the young will be carriers of the recessive allele.  A pair of homozygous dominant frogs produces no axanthic young and no carriers of the recessive allele. 

Photo of the Day

Ruby-crowned Kinglet
It’s a sign that things are about to change.  As the Neotropical warbler migration reaches its climax, other small songbirds like this Ruby-crowned Kinglet are beginning to make their southbound movements through the lower Susquehanna valley.  For a kinglet, the autumn journey is greatly abbreviated compared to that of the Neotropical species.  While the warblers and their traveling companions including vireos and flycatchers are primarily headed to the tropical climate zone for winter, kinglets spend the cold season in the temperate zone, an area encompassing most of the the continental United States and southern Canada.  These tiny birds feed mostly on small invertebrates which, particularly during the winter months, they find in spaces among the bark of mature trees.

A Rare Find Among the Migrants at Second Mountain Hawk Watch

Yesterday morning’s fallout of hundreds of nocturnally migrating birds was followed overnight by the influx of one hundred or more new arrivals atop Second Mountain in Lebanon County, Pennsylvania.  Visitors to the forest clearing used as a hawk watch lookout were treated to the antics of these colorful Neotropical species and more…

Red-eyed Vireo
…Red-eyed Vireo,…
A Great Crested Flycatcher.
…Great Crested Flycatcher,…
Least Flycatcher
…Least Flycatcher,…
A Northern Parula.
…Northern Parula,…
Juvenile Northern Paula
…juvenile Northern Paula,…
Nashville Warblers
…and quarrelsome Nashville Warblers.

These night-flying warblers, vireos, and flycatchers did again provide a thrilling show during the hours after sunrise, but today’s rarity passed through among the hundreds of migrating diurnal raptors—the tropics-bound Broad-winged Hawks—that made their way down the ridges of the lower Susquehanna valley this afternoon.

"Kettling" Broad-winged Hawks
A “kettle” of Broad-winged Hawks climbing on a thermal updraft above Second Mountain Hawk Watch.
Broad-winged Hawks
After gaining altitude, Broad-winged Hawks glide away toward the southwest in search of the next thermal updraft upon which they will rise to continue their journey to Texas, Mexico, and beyond.  Over three hundred of these raptors were counted as they passed the Second Mountain lookout today.
"Kettling" Broad-winged Hawks
Another “kettling” flock of migrating Broad-winged Hawks above Second Mountain.
Light-morph and dark-morph Broad-winged Hawks
A closer look reveals something unusual.  While the Broad-winged Hawk at the bottom center of the image displays the typical light-morph plumage, the bird in the upper left appears to be a dark-morph Broad-winged Hawk, a rarity in the eastern United States.
Dark-morph Broad-winged Hawk
A zoomed-in view of the probable dark-morph Broad-winged Hawk seen over Second Mountain this afternoon.  Populations of these variants nest in areas of central and western Canada.

The peak of the autumn Broad-winged Hawk migration will likely occur during the coming two weeks with many counting stations tallying more than one thousand birds on the best of days.  Visit one of these prominent lookout points so that you too can witness this amazing spectacle.  Click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab at the top of this page to find a hawk watch near you!

Pot o’ Gold on the Ridgetops

Bathed in glowing sunshine, a very large fallout of migrating Neotropical songbirds enlivened the forest edge atop Second Mountain in northern Lebanon County, Pennsylvania, this morning.  While last night’s flight was widespread beneath a dome of atmospheric high pressure covering the Mid-Atlantic States, this is a look at some of the 500 -1,000 migrants observed feeding on insects and other natural foods at just this single location.

Blackpoll and Black-throated Green Warblers
As the composition of the nightly flights begins to transition to species that start their migration later in the season, numbers of birds like the Blackpoll Warbler (top) are beginning to rival those of the heretofore very common Black-throated Green Warbler (bottom).
Blackpoll Warbler
A Blackpoll Warbler.
Bay-breasted Warbler
The Bay-breasted Warbler, another common species found among the fallout flock.
Tennessee Warbler
The Tennessee Warbler was today’s most abundant migrant with at least 200 birds seen moving among the other species.
Tennessee Warbler
A newly arrived Tennessee Warbler at sunrise.
Tennessee Warbler
A Tennessee Warbler snatches breakfast.
Magnolia Warbler
The Magnolia Warbler was another common find among today’s migrants.
Magnolia Warbler
A Magnolia Warbler.
Nashville Warbler
A Nashville Warbler among tangles of Mile-a-minute Weed.
Nashville Warbler
A Nashville Warbler.
Black-throated Blue Warbler
Black-throated Blue Warbler.
Adult Male Black-throated Blue Warbler
An adult male Black-throated Blue Warbler.
Northern Parula
An acrobatic Northern Parula.
Blackburnian Warbler
Blackburnian Warblers continue their southerly trek.
American Redstart
An American Redstart.
 Chestnut-sided Warbler
A Chestnut-sided Warbler feeding on Mile-a-minute Weed berries.
 Cape May Warbler
A Cape May Warbler.
Adult Male Cape May Warbler
A handsome adult male Cape May Warbler.
Swainson's Thrush
A Swainson’s Thrush.
Scarlet Tanager
Scarlet Tanagers continue to work their way south through the Lower Susquehanna River Watershed.
Olive-sided Flycatcher
A composite image of an uncommon find, a large-headed Olive-sided Flycatcher seen perched atop a dead tree snag.
Philadelphia Vireo
A brief encounter with a Philadelphia Vireo, another uncommon species.
Blue-headed Vireo
A Blue-headed Vireo, typically the last of its genus to move south in the fall, put in a welcome appearance among the hundreds of migrants.
Ruby-throated Hummingbird
A favorite diurnal migrant, the Ruby-throated Hummingbird, was seen feeding on flowers that grew from the remains of garden waste dumped illegally along the mountain road last autumn.

Many of the observers at the Second Mountain Hawk Watch commented that this morning’s fallout was by far the best they had seen anywhere in the region during recent years.  Others believed it to be the best they had ever seen.  It was indeed less like a “wave” of migrants and more like a “tsunami”.  Choosing a good viewing location and being there at the right time can improve your chances of seeing a spectacle like this.  The good news is, it looks like another big flight is currently underway, so finding a forest edge on a ridgetop or along a utility right-of-way just might pay off for you early tomorrow morning.

Nocturnal migrating birds, a southwest-bound flight down the ridges of central Pennsylvania as indicated by Doppler radar between 10:30 and 11:30 PM EDT on September 11, 2024.  (NOAA/National Weather Service image)

This Week’s Review of the Morning Fallouts

Clear, cool nights have provided ideal flight conditions for nocturnal Neotropical migrants and other southbound birds throughout the week.  Fix yourself a drink and a little snack, then sit down and enjoy this set of photographs that includes just some of the species we found during sunrise feeding frenzies atop several of the Lower Susquehanna River Watershed’s ridges.  Hurry up, because here they come…

Black-throated Green Warbler
A Black-throated Green Warbler.
Black-throated Green Warbler
The Black-throated Green Warbler was perhaps the most frequently identified treetop warbler during the most recent four mornings.
Black-throated Green Warbler
A Black-throated Green Warbler with a unique variation in the crown plumage.
Blackburnian Warbler
The Blackburnian Warbler was another plentiful species.
Cape May Warblers
Cape May Warblers have an affinity for conifers like this Eastern White Pine.
Cape May Warbler
But when traveling in mixed flocks with other migrants, Cape May Warblers can also be found feeding in the crown foliage of deciduous trees.
Tennessee Warbler
This adult Tennessee Warbler appears to be adorned in a very worn set of plumage…
Tennessee Warbler
…and its traveling companion looks like it’s overdue for a new set of feathers as well.
Nashville Warbler
Like the Tennessee Warbler, the Nashville Warbler was common among mixed flocks.
Nashville Warbler
A Nashville Warbler atop a Black Cherry.
Chestnut-sided Warbler
This Chestnut-sided Warbler was one of several found among the more common species of migrants.
Chestnut-sided Warbler
A Chestnut-sided Warbler.
Chestnut-sided Warbler
We were lucky enough to spot this male Chestnut-sided Warbler sporting his namesake flank feathers.
 Black-and-white Warbler
A Black-and-white Warbler uses its nuthatch-like feeding behavior to search the tree bark for edible invertebrates.
Common Yellowthroat
To see the Common Yellowthroat, one must cease looking upward into the high canopy and instead give the aching neck a rest by peering into the low vegetation at the forest edge.
Magnolia Warbler
While checking the low growth, keep an eye open for other migrants among the shrubs and tangles. This Magnolia Warbler glows in the rays of a rising sun as it searches for a meal after a long night of travel.
House Wren
Here we found a perky little House Wren.
Eastern Wood-Pewee
Back in the middle and upper reaches of the trees, we find what has been by far the most numerous of the flycatchers seen during our visits to fallout sunrises.  Eastern Wood-Pewees are appearing in very good numbers and can be seen quarreling and battling for hunting perches from which they are ambushing flying insects.
 Eastern Wood-Pewee
An Eastern Wood-Pewee fiercely defending its hunting perch.
Eastern Wood-Pewee
An Eastern Wood-Pewee.
Least Flycatcher
The numbers of migrating Least Flycatchers and other members of the genus Empidonax may be reaching their seasonal peak this week.
Scarlet Tanagers
Scarlet Tanagers are currently a common find following nocturnal flights.
Scarlet Tanager
A Scarlet Tanager peers down from the top of a Red Maple.
Rose-breasted Grosbeak
Did you hear a loud squeak in the treetops?  It could be a southbound Rose-breasted Grosbeak stopping by for the day.
Rose-breasted Grosbeak
A Rose-breasted Grosbeak in a dead tree snag.
Swainson's Thrush
The Neotropical thrushes are beginning to move south now as well.  We found this newly arrived Swainson’s Thrush at Rocky Ridge County Park in York County during sunrise this morning.
Red-eyed Vireo
Not surprisingly, the Red-eyed Vireo is one of the most numerous of the migrants seen feeding in the deciduous canopy following a nocturnal flight event.  It’s not at all unusual to see dozens filing the trees around a ridgetop overlook or along a forest edge.  Be certain to check these congregations carefully, especially the groups of birds feeding in the lower branches of tall timber or in the tops of smaller trees.  This week we found…
Yellow-throated Vireo
…several hungry Yellow-throated Vireos arriving after nocturnal flights,…
Philadelphia Vireo
…and a Philadelphia Vireo (Vireo philadelphicus) at the hawkwatch at Rocky Ridge County Park in York County.
Red-breasted Nuthatch
Though not a Neotropical migrant, the easier-heard-than-seen Red-breasted Nuthatch is beginning to wander south into the lower Susquehanna region.  Most of these birds will eventually continue on to the pine forests of the southern United States for winter, but a few could remain to become seasonal visitors at feeding stations.
Ruby-throated Hummingbird
Ruby-throated Hummingbirds are on the move; their migration to the tropics is well underway and nearing its peak.  Ruby-throats are diurnal migrants that do a majority of their flying during the hours of daylight.  The notable exception: the nighttime portion of the long southbound flight some of the birds make to cross the Gulf of Mexico.
Red-headed Woodpecker
The Red-headed Woodpecker is another diurnal migrant.   This denizen of temperate climates is currently beginning to move to its wintering grounds, an area that extends from the latitudes of the lower Susquehanna south to the Gulf of Mexico and central Texas.
Juvenile Red-headed Woodpecker
A juvenile Red-headed Woodpecker during a brief pit stop.
Cedar Waxwings
The flights of roving bands of masked Cedar Waxwings continue.  Their numbers appear to be an improvement over those of 2023.
Broad-winged Hawk
At regional hawk-counting stations, observers are seeing more Broad-winged Hawks and other species beginning to move through.
"Kettling" Broad-winged Hawks
The frequency of Broad-winged Hawks passing the lookouts one at a time is giving way to the occurrence of larger and larger “kettling” groups that search out thermal updrafts to save energy while migrating.  By mid-September each of these “kettles” can include one hundred birds or more.  On the peak days, the daily Broad-winged Hawk totals can reach one thousand or more.
Broad-winged Hawk
A Broad-winged Hawk soaring to gain lift from a thermal updraft above a hawkwatch lookout.

The migration is by no means over; it has only just begun.  So plan to visit a local hawkwatch or other suitable ridgetop in coming weeks.  Arrive early (between 7 and 8 AM) to catch a glimpse of a nocturnal migrant fallout, then stay through the day to see the hundreds, maybe even thousands, of Broad-winged Hawks and other diurnal raptors that will pass by.  It’s an experience you won’t forget.

Broad-winged Hawk Gliding Away to the Southwest
A Broad-winged Hawk gliding away to the southwest.

Be certain to click the “Birds” tab at the top of this page for a photo guide to the species you’re likely to see passing south through the lower Susquehanna valley in coming months.  And don’t forget to click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab to find a hawk-counting station near you.

More birds are on the way.  Here’s a look at this evening’s liftoff of nocturnal migrants detected by National Weather Service Radar in State College, Pennsylvania.  (NOAA/National Weather Service Doppler Radar image)

A Prescribed Fire Site After the Burn

Back on March 24th, we took a detailed look at the process involved in administering prescribed fire as a tool for managing grassland and early successional habitat.  Today we’re going turn back the hands of time to give you a glimpse of how the treated site fared during the five months since the controlled burn.  Let’s go back to Middle Creek Wildlife Management Area for a photo tour to see how things have come along…

Prescribed Fire application in March
Pennsylvania Game Commission crews administering prescribed fire on a grassland demonstration site back on March 16.
Prescribed Fire Site in May
By late May, native herbaceous perennial wildflowers including Joe-pye Weed had re-greened the site.  One of the goals of the burn was to kill fire-sensitive woody plants, thus preventing the process of succession from reforesting the site.
Prescribed Fire Site in May
The scorched, lifeless remains of small trees and shrubs indicate that that goal was met.
Yellow-breasted Chat in May
Because prescribed fire is administered in a mosaic pattern that permits some early successional growth to remain until the next burn, birds including this thicket-nesting Yellow-breasted Chat are able to take advantage of the mixed habitat during their breeding season in May and June.
Prescribed Fire Site in August
By August, the site is a haven for native plants and animals.
Native Warm-season Grasses and Wildlflowers in August
The burn has promoted the growth and late-summer bloom of fire-tolerant native wildflowers and warm-season grasses…
Indiangrass in Flower
…including Indiangrass,…
Big Bluestem
…Big Bluestem…
Thin-leaved Coneflower, a plant also known as Brown-eyed Susan.
…Thin-leaved Coneflower (Rudbeckia triloba), a plant also known as Brown-eyed Susan,…
Joe-pye Weed
…and Joe-pye Weed, a plant butterflies find irresistible.
Eastern Tiger Swallowtail collecting nectar from Joe-pye Weed.
Eastern Tiger Swallowtail collecting nectar from Joe-pye Weed.
Black-morph Eastern Tiger Swallowtail
A black-morph Eastern Tiger Swallowtail collecting nectar from Spotted Knapweed (Centaurea steobe micranthos), a non-native invasive plant found growing in an area of the burn site missed by this year’s fire.  While many non-native plants are unable to survive the flames and heat produced by prescribed fire, it isn’t an absolute cure-all.  It doesn’t eliminate all invasive plants, it just keeps them from dominating a landscape by out-competing native species.  Left unmanaged, Spotted Knapweed is a tough perennial invasive that can easily become one the species able to overtake a vulnerable grassland.  It can be a stubborn survivor of some prescribed burns.  On the plus side, butterflies really like it.
American Goldfinch
By August, native grassland plants in the prescribed fire area were already providing an abundance of seeds for birds including this American Goldfinch.
Carolina Grasshopper
For larger birds like turkeys and pheasants, an abundance of Carolina Grasshoppers are providing a protein-dense food source in managed grasslands.
Black Saddlebags
And tiny flying insects, a nuisance to us as we take a stroll alongside the grasslands, are a meal taken on the wing by dragonflies including this Black Saddlebags.

Elsewhere around the refuge at Middle Creek, prescribed fire and other management techniques are providing high-quality grassland habitat for numerous species of nesting birds…

Bobolink
Bobolinks nested both in areas subjected to controlled burns…
Bobolink in Hay Field
…and in hay fields where mowing was delayed until the nesting season, including the fledging process, was completed earlier this month.
Grasshopper Sparrow
As advertised, Grasshopper Sparrows nested in these fields as well.

We hope you enjoyed this short photo tour of grassland management practices.  Now, we’d like to leave you with one last set of pictures—a set you may find as interesting as we found them.  Each is of a different Eastern Cottontail, a species we found to be particularly common on prescribed fire sites when we took these images in late May.  The first two are of the individuals we happened to be able to photograph in areas subjected to fire two months earlier in March.  The latter two are of cottontails we happened to photograph elsewhere on the refuge in areas not in proximity to ground treated with a prescribed burn or exposed to accidental fire in recent years.

Eastern Cottontail
Eastern Cottontail at a site subjected to prescribed fire earlier in the spring.
Eastern Cottontail
Eastern Cottontail at a site subjected to prescribed fire earlier in the spring.

These first two rabbits are living the good life in a warm-season grass wonderland.

Eastern Cottontail with ticks.
Eastern Cottontail at a site not subjected to any recent fire activity.
Eastern Cottontail with ticks.
Eastern Cottontail at a site not subjected to any recent fire activity.

Oh Deer!  Oh Deer!  These last two rabbits have no clock to track the time; they have only ticks.  Better not go for a stroll with them Alice—that’s no wonderland!  I know, I know, it’s time to go.  See ya later.

Aphrodite Fritillary

The Aphrodite Fritillary (Speyeria aphrodite), also known simply as the Aphrodite, is a brush-footed butterfly of deciduous, coniferous, and mixed forests.  We found this female in a grassland margin between woodlots where prescribed fire was administered during the autumn of 2022 to reduce accumulations of natural fuels and an overabundance of invasive vegetation.  A goal of the burn was to promote the growth of native species including the violets (Viola species) favored as larval host plants by this and other fritillaries.

Aphrodite Fritillary
A female Aphrodite Fritillary collecting nectar from a thistle flower.

By the time these adult butterflies make their reproductive flights in late summer, the violets that serve as larval host plants have gone dormant.  To find patches of ground where the violets will come to life in spring, the female Aphrodite Fritillary has an ability to sense the presence of dormant roots, probably by smell.  Upon finding an area where suitable violets will begin greening up next year, she’ll deposit her eggs.  The eggs overwinter, then hatch to feed on the tender new violet leaves of spring.

Aphrodite Fritillary
A female Aphrodite Fritillary.  A prescribed burn, when administered during spring to manage fritillary habitat, is applied only to a portion of the land parcel each year to avoid decimating an entire population of the larvae during the first instar of their life cycle, a time when they are vulnerable to fire.
Aphrodite Fritillary
Our female Aphrodite Fritillary busily gathers nutritious nectar to provide sufficient energy for the critical process of mating and egg production.  What’s the thistle that this goddess of love and procreation is pollinating?…It’s a non-native invasive, the Bull Thistle (Cirsium vulgare), a species that readily colonizes new areas by producing an abundance of airborne seeds.  Continued management of this site with periodic applications of prescribed fire will prevent Bull Thistle and other invasives from overtaking the habitat during coming years.

Allegheny Vine

Here’s a native plant you don’t see very often, but Ruby-throated Hummingbirds have a knack for finding and adoring it within the limited habitat where it still exists.

Allegheny Vine in Bloom
Allegheny Vine (Adlumia fungosa), also known as Climbing Fumitory or Mountain Fringe, is a seldom-found biennial herbaceous plant in the poppy family (Papaveraceae).  Both its divided leaves and drooping clusters of flowers might remind the observer of a more familiar member of the poppy family, the spring-blooming Dutchman’s Breeches.  But unlike the low-growing Dutchman’s Breeches, Allegheny Vine ascends nearby shrubs and small trees with trailing stems that add a garland-like pizzazz to the summertime foliage.
Ruby-throated Hummingbird at Allegheny Vine
Seen here creeping atop a small Sassafras (Sassafras albidum) tree, Allegheny Vine seldom escapes notice by the Ruby-throated Hummingbird, a primary pollinator of the plant.
Ruby-throated Hummingbird at Allegheny Vine
Allegheny Vine grows on moist, rocky slopes and blooms in late summer, just in time to refuel migrating Ruby-throated Hummingbirds.

Not likely to thrive in deep forest cover, Allegheny Vine is a denizen of edge habitat.  The species is dependent on some type of disturbance to maintain suitable growing conditions.  The plants seen here were found flowering in an area that had experienced a fire prior to last year’s growing season.  It is therefore quite possible that the fire completed the stratification process and triggered long-dormant seeds to germinate last spring or summer to develop a basal plant which matured and flowered during this second summer of the biennial’s growth.  On a forested slope opposite this site, a first-ever prescribed burn was conducted in March of this year to eliminate accumulated fuel and replicate a natural fire cycle.  With a little luck, this forest management approach may prompt additional long-dormant Allegheny Vine seeds to germinate and form basal plants this year for maturation in 2025.  Without man-made disturbances, Allegheny Vine may remain viable as a species by enduring seed dormancy periods of 40-100 years or more between fires, lightning strikes, wind storms, ice accumulations, and other events which clear the canopy and encourage growth.

Ruby-throated Hummingbird at Allegheny Vine
Many years in the making, Allegheny Vine nectar must be delectable because the hummers can’t leave it alone.  And another plus, with a little help from prescribed fire, this native creeping plant seems to be holding its own while in direct competition with invasive Mile-a-minute Weed (leaves in lower right).

A Tricky Flycatcher To Identify

The tiny flycatchers of the genus Empidonax are notoriously difficult to identify by visual clues alone.  Determining the species by sight requires a good look under ideal conditions.  Even then, these birds are a tricky lot.  Don’t believe it?  Take a gander at these photos of an Empidonax flycatcher found atop Second Mountain in Lebanon County at sunrise this morning…

Yellow-bellied Flycatcher
One of the telltale signs of an Empidonax flycatcher from outside the group of eastern species is the presence of an expanded rear edge of a well-defined eye ring.
Yellow-bellied Flycatcher
Only the Pacific-slope and Cordilleran Flycatchers, groups currently lumped together by taxonomists as the Western Flycatcher, exhibit the teardrop-shaped eye ring.  In the lower Susquehanna region, Western Flycatchers have been recorded as vagrants during autumn and in early winter on several occasions, most recently along the river in Conoy Township, Lancaster County, in December of 2023.  (See post from December 20, 2023)
Yellow-bellied Flycatcher
For now, that 2023 record will remain the most recent.  With a turn of its head providing a better angle in direct sunlight, the apparent expansion of the rear portion of the eye ring turns out to be little more than a pale post-ocular feather on this bird.  The broad (but uniform) eye ring, rounded head, small bill, short tail, and the unbroken coloration of the underside areas all conspire to indicate that this is probably a Yellow-bellied Flycatcher (Empidonax flaviventris).  Disappointing?  Hardly.  Yellow-bellied Flycatchers are strictly migrants in the Lower Susquehanna River Watershed.  They are rarely seen as they pass through traveling to and from their breeding grounds in the moist coniferous forests, bogs, and swamps of the northernmost United States and southern Canada.  A Neotropical species, the Yellow-bellied Flycatcher winters in southern Mexico and Central America.

Southbound Flights: On Their Way Both Night and Day

It’s hard to believe, but for almost two months now, sandpipers, plovers, and terns have been filtering south through the Lower Susquehanna River Watershed on their way to the Atlantic coastline as they complete the first leg of their long autumn migration—a journey that will take some species all the way to the far reaches of the South American continent for winter.

Caspian Terns and Osprey
Migrating Caspian Terns and an Osprey take a break on a lower Susquehanna valley gravel bar.

As August draws to a close, these early birds are being joined by widespread nocturnal flights of Neotropical migrants—those species, primarily songbirds, on their way to wintering grounds which lie exclusively south of the continental United States.

To catch a glimpse of these night-flying avians, your best bet may be to position yourself on the crest of a ridge or along a linear break in the forest such as a utility right-of-way where waves of warblers, vireos, flycatchers, and other Neotropical passerines sometimes feed on invertebrates after making landfall at daybreak.  Pick a place where the trees are bathed in the warm light of the rising sun and be there by 7 A.M. E.D.T.  The activity can be tremendous, but it usually ends between 8 and 9.

Red-eyed Vireo
One of more than half a dozen Red-eyed Vireos seen during a daybreak fallout at Second Mountain Hawkwatch in Lebanon County earlier this week.
Blackburnian Warbler
During sunrise, a just-arrived Blackburnian Warbler checks the foliage of a ridgetop Red Maple for insects.
Least Flycatcher
A Least Flycatcher quietly searches the shrubby growth along the forest edge for a morning meal.
Black-and-white Warbler
A Black-and-white Warbler in the first hour of sunlight after a big nocturnal flight.
Scarlet Tanager
A Scarlet Tanager having a look around.  This individual and other migrating birds may be here for a few days before moving on.
Black-throated Green Warbler
A Black-throated Green Warbler in a treetop glowing with the light of sunrise.
Chestnut-sided Warbler
A hungry Chestnut-sided Warbler inspects limbs, leaves, and twigs looking for nourishment after an all-night flight.

Diurnal migrants, birds that make their movements during the daylight hours, are ramping up their flights now as well.  Broad-winged Hawks, Bald Eagles, and falcons are currently being tallied at hawk-counting stations throughout the northeast.  Many of those lookouts are seeing Ruby-throated Hummingbirds, swallows, and other daytime migrants too.

Broad-winged Hawk
While many diurnal migrants gather in flocks as a method of defense against predators, Broad-winged Hawks congregate as a reconnaissance measure.  Not waiting around for strong autumn winds to be deflected upwards by the region’s numerous ridges, these Neotropical birds migrate early enough in the season to rely upon thermal updrafts from sun-heated surfaces to provide lift, gain altitude, and save energy during their long trip.  By traveling in groups, there are collectively able to better locate and utilize rising air columns as they progress southwesterly along their route.  Broad-winged Hawks travel to Central and South America for winter.  Their numbers in the Lower Susquehanna River Watershed will peak during the third week of September.
American Kestrel
Many American Kestrels transit our area in August and early September, a time coinciding with flights of migratory dragonflies, insects upon which they and another falcon, the Merlin, frequently prey.
Chimney Swifts
Chimney Swifts are fast-flying diurnal migrants.  They are beginning to congregate into larger groups in preparation for their departure.  Some are already on the move.
Cedar Waxwing
Cedar Waxwings are currently being seen in roving flocks throughout the region.  Their migration is less of a point-to-point flight and more of a continuous wandering in search of berries and other wild foods.
American Goldfinch
Not everyone is yet ready to go.  American Goldfinches are still in the midst of their nesting cycle and won’t begin leaving until the young are on their own and colorful adult males like this one are beginning to molt into their drab winter plumage.

Autumn migration flights are an ever-changing process, with different species peaking at different times throughout the season.  In these months just after the nesting season, each of these species is more numerous than at any other time of the year.  And of course, the more often we as observers get out and have a look, the more of them we’ll see.

Be certain to click the “Birds” tab at the top of this page for a photo guide to the species you’re likely to see passing through the lower Susquehanna valley this fall.  Nearly four months of autumn hawk migration flights lie ahead, so don’t forget to click the “Hawkwatcher’s Helper: Identifying Bald Eagles and other Diurnal Raptors” tab to find a hawk-counting station near you, then stop by for a visit or two.  See you there!

A large nightfall liftoff of nocturnal migrating birds is shown here on this evening’s State College, Pennsylvania, Doppler Radar base velocity loop.  Returns indicating birds moving toward the radar site (the white dot in the center of the color mass) are shown in green, and those indicating birds moving away are indicated in red.  This is a big flight headed generally in a south-southwest direction.  (NOAA/National Weather Service Doppler Radar image)

Heat Flux Processes in Streams and Their Impact on Coldwater and Coolwater Fishes

The deluge of rain that soaked the lower Susquehanna watershed during last week is now just a memory.  Streams to the west of the river, where the flooding courtesy of the remnants of Hurricane Debby was most severe, have reached their crest and receded.  Sliding away toward the Chesapeake and Atlantic is all that runoff, laden with a brew of pollutants including but not limited to: agricultural nutrients, sediment, petroleum products, sewage, lawn chemicals, tires, dog poop, and all that litter—paper, plastics, glass, Styrofoam, and more.  For aquatic organisms including our freshwater fish, these floods, particularly when they occur in summer, can compound the effects of the numerous stressors that already limit their ability to live, thrive, and reproduce.

(Environmental Protection Agency image)

One of those preexisting stressors, high water temperature, can be either intensified or relieved by summertime precipitation.  Runoff from forested or other densely vegetated ground normally has little impact on stream temperature.  But segments of waterways receiving significant volumes of runoff from areas of sun-exposed impervious ground will usually see increases during at least the early stages of a rain event.  Fortunately, projects implemented to address the negative impacts of stormwater flow and stream impairment can often have the additional benefit of helping to attenuate sudden rises in stream temperature.

Stream Subjected to Agricultural Runoff
While a row of trees along a creek can help provide protection from the thermal impact of the sun, a vegetative riparian buffer must be much wider to be effective for absorbing, cooling, and treating runoff from fields, lawns, and paved surfaces.  This buffer is too narrow to prevent surface runoff from polluting the water.

Of the fishes inhabiting the Lower Susquehanna River Watershed’s temperate streams, the least tolerant of summer warming are the trouts and sculpins—species often described as “coldwater fishes”.  Coldwater fishes require water temperatures below 70° Fahrenheit to thrive and reproduce.  The optimal temperature range is 50° to 65° F.  In the lower Susquehanna valley, few streams are able to sustain trouts and sculpins through the summer months—largely due to the effects of warm stormwater runoff and other forms of impairment.

Blue Ridge Sculpin
Sculpins, including the Blue Ridge Sculpin (Cottus caeruleomentum) seen here, are native coldwater fishes which, during the 11,000 years since the last glacial maximum, have had the availability of their favored habitat sharply reduced by warming water temperatures and a rising Atlantic.  During this interval, seawater has inundated the path of the “Late” Pleistocene lower Susquehanna which passed through the section of flooded river watershed we now call Chesapeake Bay and continued across the continental shelf to what was, during the glacial maximum, the river’s mouth at Norfolk Canyon.  Today, cut off from neighboring drainage basins, sculpins survive exclusively in cold headwaters, and only in those where human alterations including pollution, dams, channelization, and reduced base flow haven’t yet eliminated their isolated populations.  Formerly believed to be composed of two widespread North American species, the Slimy Sculpin (Cottus cognatus) and the Mottled Sculpin (Cottus bairdii), study in recent decades is discovering that sculpin populations in the present-day lower Susquehanna and neighboring Potomac headwaters consist of at least three newly delineated species: Blue Ridge Sculpin, Potomac Sculpin (Cottus gerardi), and Checkered Sculpin (Cottus sp.), the latter an as yet undescribed species found only in the refugium of limestone springs in the Potomac drainage in West Virginia; Frederick and Washington Counties, Maryland; and Franklin County, Pennsylvania.  (United States Geological Survey image)
Ice Age Susquehanna
Stare at this for a little while, you’ll figure it out…………More than 11,000 years ago, during the last glacial maximum, when sea level was about 275 feet lower than it is today, there was no Chesapeake Bay, just a great Susquehanna River that flowed to the edge of the continental shelf and its mouth at Norfolk Canyon.  It was a river draining taiga forests of pine, spruce , and fir, and it carried along the waters of all the present-day bay’s tributaries and more.  The section of the river’s watershed we presently call the lower Susquehanna was, at the time, the upper Susquehanna watershed.  Brook Trout and sculpins had the run of the river and its tributaries back then.  And the entire watershed was a coldwater fishery, with limestone and other groundwater springs providing not refuge from summer heat, but a place to escape freezing water.  (United States Geological Survey base image)
Norfolk Canyon, the mouth of the Susquehanna River during the most recent glacial maximum, now lies more than 275 feet below the surface of the ocean and plunges to more than a mile in depth along the finger of out wash from the gorge.  (United States Geological Survey image)
Rainbow. Brown, and Brook Trout
Tens of thousands of trout are raised in state-operated and cooperative nurseries for stocking throughout the lower Susquehanna valley.  These rearing facilities are located on spring-fed headwaters with sufficient flow to assure cold temperatures year round.  While the Rainbow Trout and Brown Trout (Salmo trutta) are the most commonly stocked species, the Brook Trout (Salvelinus fontinalis) is the only one native to American waters.  It is the least tolerant of stream warming and still reproduces in the wild only in a few pristine headwaters streams in the region.  During spring, all three of these species have been observed on rare occasions entering the fish lift facilities at the hydroelectric dams on the river, presumably returning to the Susquehanna as sea-run trout.

Coldwater fishes are generally found in small spring-fed creeks and  headwaters runs. Where stream gradient, substrate, dissolved oxygen, and other parameters are favorable, some species may be tolerant of water warmer than the optimal values.  In other words, these temperature classifications are not set in stone and nobody ever explained ichthyology to a fish, so there are exceptions.  The Brown Trout for example is sometimes listed as a “coldwater transition fish”, able to survive and reproduce in waters where stream quality is exceptionally good but the temperature may periodically reach the mid-seventies.

Eastern Blacknose Dace
The Eastern Blacknose Dace is sometimes classified as a “coldwater transition fish”.   It can be found in headwaters runs as well as in creeks with good water quality.
Longnose Dace
The Longnose Dace is another “coldwater transition fish” known only from clear, clean, flowing waters.

More tolerant of summer heat than the trouts, sculpins, and daces are the “coolwater fishes”—species able to feed, grow, and reproduce in streams with a temperature of less than 80° F, but higher than 60° F.  Coolwater fishes thrive in creeks and rivers that hover in the 65° to 70° F range during summer.

Creek Chubs
The Creek Chub is a familiar species of “coolwater fish” seldom found remaining in waters exceeding 80 degrees Fahrenheit.
The Yellow Perch (Perca flavescens) was perhaps the most frequently targeted coolwater “gamefish” in the Lower Susquehanna River Watershed prior to the introduction of the Northern Pike (Esox lucius) and Muskellunge (Esox masquinongy).  Today’s prevalence of warmwater streams and the dozens of species of non-native predatory fishes now naturalized within them have left the Yellow Perch populations greatly reduced and all but forgotten by anglers.  Out of sight, out of mind.  (National Park Service image)

What are the causes of modern-day reductions in coldwater and coolwater fish habitats in the lower Susquehanna River and its hundreds of miles of tributaries?  To answer that, let’s take a look at the atmospheric, cosmic, and hydrologic processes that impact water temperature.  Technically, these processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time, frequently expressed as watts per meter squared (W/m²).  Without getting too technical, we’ll just take a look at the practical impact these processes have on stream temperatures.

HEAT FLUX PROCESSES IN A SEGMENT OF STREAM

Heat Flux Processes on Stream and River Segments.  These processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time.  (Environmental Protection Agency image)
      • INCOMING TEMPERATURE AND FLOW—The baseline temperature of stream water entering a given segment of waterway is obviously the chief factor determining its temperature when exiting that segment.  Incoming temperature and flow also determine the water’s susceptibility to heat absorption or loss while transiting the segment.  Lower flows may subject the given volume of water to a greater loss or gain of heat energy during the time needed to pass through the segment than the same volume at a higher flow.  Lower flows may also reduce stream velocity and extend a given volume of water’s exposure time to the exchange of heat energy while moving through the segment.  Generally speaking…
        1. …the higher the stream flow, the less a given volume of that stream’s  water may be impacted by the effects of the heat flux processes within the segment.
        2. …the lower the stream flow, the more a given volume of that stream’s water may be impacted by the effects of the heat flux processes within that segment.
        3. …the temperature and flow rate of precipitation entering the segment are factors that determine the impact of its heat energy transfer to or from a given volume of the stream’s waters.
        4. …the temperature and flow rate of runoff and point-source discharges entering the segment are factors that determine the impact of their heat energy transfer to or from a given volume of the stream’s waters.
Stormwater Discharge into Channelized Creek
Stormwater from impervious surfaces including roads, parking lots, roofs, and lawns quickly impacts temperatures in small creeks.  Channelized  streams are availed few of the positive attributes provided by many of the heat flux processes we’re about to see.  They therefore suffer from severe impairment and are exposed to temperature extremes that few aquatic organisms can survive.  Runoff from sun-heated pavement during a summer thunderstorm can often exceed 100 degrees Fahrenheit and can, at sufficient flow rate, quickly raise the temperature of a small stream to well over 90 degrees.
Stormwater Runoff
Stormwater runoff not only poses a thermal threat to waterways, its a significant source of a wide variety of pollutants.
      • GROUNDWATER INPUT—In streams connected to the aquifer, the temperature in a flowing segment can be impacted by the influx of cold groundwater.  With temperatures ranging from about 52° to 60° Fahrenheit, groundwater will absorb heat from the stream in summer, and warm it in the winter.  In warmwater streams, coldwater and coolwater fishes will often seek areas of the substrate where groundwater is entering for use as refugium from the summer heat.  Yellow Perch in the lower Susquehanna are known to exhibit this behavior.
Creeks and rivers connected to the aquifer and receiving supplemental flow from it are known as “gaining streams”. These streams frequently feed water into the aquifer as well. (United States Geological Survey image)
When flowing through an area experiencing drought or an excessive removal of groundwater (lots of wells, etc.), a waterway can become a “losing stream”, one that surrenders a portion of its flow to recharge the aquifer.  Further downstream, the reduced flow can make such a creek or river more susceptible to the effects of heat flux processes.  (United States Geological Survey image)
Seriously depleted aquifers can lead to a “disconnected stream”.  Smaller waterways subjected to these conditions will sometimes lose all their flow to the ground, often causing a catastrophic failure of the aquatic ecosystem supported therein.  (United States Geological Survey image)
Urban Flooding and Dry Streambed
Urban runoff overwhelms this small stream with polluted water than can reach temperatures of 100 degrees or more (left), then lets it high and dry with no baseflow during periods of dry weather (right) as the waterway becomes disconnected from the much-depleted aquifer.
Stormwater Retention Basin
Well-designed and properly constructed stormwater retention basins not only recharge groundwater supplies for wells and streams, they can also help prevent thermal pollution in waterways.  Planted with native wetland species and allowed to thrive, they can become treasured wildlife islands in otherwise inhospitable environs.  The benefits don’t stop there; plants also help sequester nutrients contained in the runoff.
      • HYPORHEIC EXCHANGE—Related to groundwater input, hyporheic exchange is the slow movement of water through the rock, sand, gravel, and soils composing the streambed, saturated shoreline, shallow aquifer, and connected floodplain of a creek or river.  As a heat flux process, hyporheic exchange helps moderate extremes in seasonal water temperatures by conducting energy between the solid materials in the zone and the flowing water.  Hyporheic zones are important habitats for many species of aquatic invertebrates and spawning fish.  Natural chemical processes within these zones convert ammonia-producing wastes into nitrite, then nitrate, allowing it to be absorbed as food by plants growing in the stream or in the alluvium within the zone.  Vegetation removal, channelization, legacy sediments, silt deposits, and man-made walls and dams can negate the benefits of hyporheic exchange.
Exchange of surface and ground water within the hyporheic zone is most directly associated with high-gradient (left) and meandering (right) segments of streams. (United States Geological Survey image)
Legacy Sediments and Fill
Very common on streams in the lower Susquehanna valley are these accumulations of legacy sediments at the sites of former mill ponds.  After the dams were removed, the creeks began eroding their way down through the mire as they tried to reestablish their floodplains and find their native substrate.  These trapped waterways are not only cut off from their hyporheic zones, they’re now a major source of nutrient and sediment pollution.  Misguided landowners like this one frequently dump fill into these sites to “save their land” and “control flooding”.  The fill and materials added to “shore up the banks” do nothing to fix what ails the creek, but instead displace more water to make the impact of flooding even more widespread.
Flooplain and Stream Restoration
Rehabilitation projects that remove legacy sediments help restore hyporheic exchange by reconnecting the stream to its underlying geology, its floodplain, and its wetlands.  Rising waters remain in the floodplain where they get a good bio-scrubbing and help replenish the creek and groundwater supply.  As the experts say, “floodplains are for flooding.”
      • ATMOSPHERIC EXCHANGE (CONVECTION, EVAPORATION)—Primarily a process by which a stream loses heat energy and cools its waters, atmospheric exchange is also a means by which a warm air mass can relinquish heat to cooler waters and thus increase their temperature.  This phenomenon can be dramatically enhanced when a stream passes through a so-called urban heat island where air temperatures remain warm through the night.  Convection, the movement of heat energy through a fluid (liquid or gas), causes warmer, less-dense water to rise to the surface of a stream, particularly where there is minimal turbulence.  When the air above is cooler than the water’s surface layer, the stream will conduct heat energy across the water/atmosphere interface causing the warmed air molecules to rise in a convection column.  If the atmospheric relative humidity is less than 100%, some surface water will vaporize—a process that expends more of the stream’s heat energy.  The rate of convective and evaporative cooling in a given stream segment is directly related to the degree of difference between the water temperature and air temperature, and to the relative humidity in the air mass above the lake, creek, or river.  The mechanical action of stream turbulence including rapids, riffles, and falls increases the contact area between air and water to maximize the atmospheric exchange of heat energy.  The convective air current we call surface wind has a turbulent wave-producing effect on water that can also maximize atmospheric exchange; think of a cold autumn wind robbing heat energy from a warm lake or river or a hot summer wind imparting its heat to a cooler creek.  These exchanges are both conductive in nature (air-to-water/water-to-air) and evaporative, the latter being expedited by the movement of dry air over warm water.
Tessellated Darter
Usually classified as one of the coolwater fishes, the bottom-dwelling Tessellated Darter can thrive in the warmer creeks and in the main stem of the Susquehanna by inhabiting riffles where atmospheric exchange in the form of increased evaporation helps reduce temperatures and convective currents carry the cooler, well-oxygenated water to the streambed.
Three mile Island Unit 1 Cooling Towers
Humans utilize the concept of atmospheric exchange, adopting the phenomena of evaporation and convection to cool the hot waters produced during electric generation and other industrial processes before discharge into a lake or river.
      • STREAMBED CONDUCTIVE EXCHANGE—In the lower Susquehanna watershed, there may be no better natural example of streambed conductive exchange than the Triassic-Jurassic diabase pothole bedrocks of Conewago Falls on the river at the south end of Three Mile Island.
During sunny days, the massive diabase pothole rocks at Conewago Falls absorb solar (shortwave) radiation, then conduct that heat energy into the flowing water, often continuing to pass the accumulated warmth into the river during the night.  On cloudy days, the riverbed collects longwave atmospheric radiation, a heat flux process that yields significantly less energy for conduction into the rapids, riffles, and pools of the falls.  During periods of low river flow, the heating effect of streambed conductive exchange can become magnified.  Compared to conditions that prevail when torrents of turbid water are rushing through the falls, partially exposed bedrock surrounded by clear water collects radiated energy much more efficiently, then conducts the heat to a greatly reduced volume of passing water.  During summer and autumn, this process can create a mix of temperature zones within the falls with warmer water lingering in slow-moving pools and cooler water flowing in the deeper fast-moving channels.  Along the falls’ mile-long course, a haven is created for aquatic organisms including warmwater and some coolwater fishes, oft times attracting anglers and a variety of hungry migrating birds as well.
Fallfish
Classified as one of our coolwater fishes, the Fallfish finds favorable conditions for feeding, growing, and spawning in the well-oxygenated waters of Conewago Falls.
Northern Hog Sucker
Though the lower Susquehanna River is classified as a warmwater fishery, the Northern Hog Sucker (Hypentelium nigricans), another of our native coolwater fishes, finds the fast-moving waters of Conewago Falls to its liking.  Northern Hog Suckers are known to inhabit streams cold enough to host trout.  They exhibit remarkable home range fidelity, sometimes spending their entire lives occupying the same several hundred feet of waterway.  Northern Hog Suckers are often designated an indicator of good water quality, intolerant of many stream impairment parameters.  Their presence in Conewago Falls provides testament to the quality of the warmwater fishery there.
Severely Impaired Channelized Stream
An unnatural example.  The reduced base flow in this channelized and severely impaired creek has been rendered vulnerable to the negative impacts of several heat flux processes including streambed conductive exchange.  Urban stormwater/surfacewater inflow, solar (shortwave) radiation, and heat conducted into the stream from the masonry walls, curbs, and raceway can all conspire to cook aquatic organisms with life-quenching summer water temperatures exceeding 90 degrees Fahrenheit.
      • SOLAR (SHORTWAVE) RADIATION—The sun provides the energy that fuels the earth’s complex climate.  The primary heat flux process that heats our planet is the absorption of solar radiation in the shortwave spectrum, which includes ultraviolet, visible, and infrared frequencies at the upper end of the longwave spectrum.  Streams and other bodies of water absorb the greatest amounts of solar (shortwave) radiation during the weeks around summer solstice when the sun at mid-day is closer to zenith than at any other time of the year.  However, the heating impact of the radiation may be greatest when the volume of water in the creek, river, or lake is at its minimum for the year—often during early fall.
The rate, measured in watts per square meter, at which solar (shortwave) energy is directly radiated to a given area on the earth’s surface (including streams and other waters) is determined by: solar activity, the angle of the sun in the sky, aspect (slope) of the receiving surface, the opacity of the overlying atmosphere, and the distance of the earth from the sun.  The former varies with the year’s seasons, the time of day, and the latitude of a given area.  The latter is currently at its annual minimum when earth is at perihelion during the early days of January, thus providing the northern hemisphere with a little bump in radiation during the shortest days of the year when the sun is at its lowest angle in the sky.  (NASA image)
A varying portion of the solar (shortwave) radiation reaching the earth is reflected back into space by clouds.  A smaller share is absorbed by the atmosphere, thus heating it.  An even lesser quantity is reflected back into space by water and land.  The remainder of the energy is absorbed by the planet’s surfaces, its water and land. (NASA image)
      • INCIDENT SHORTWAVE RADIATION—Also known as insolation (incoming solar radiation), incident shortwave radiation is the sum total energy of both the direct solar radiation that travels to the earth’s surface unaffected by the atmosphere and the diffuse radiation, waves that have been weakened and scattered by constituents of the atmosphere before reaching the planet’s surface.  On a cloudy day, the warming of terrestrial surfaces including streams and other bodies of water is the result of diffuse radiation.  On days with any amount of sunshine at all, both direct and diffuse radiation heat our waters and lands.
Pumkinseed
Warmwater fishes such as the native Pumpkinseed (Lepomis gibbosus) thrive in sun-drenched 70-to-85-degree waters as long as other heat flux processes prevent sudden temperature increases and oxygen depletion.
Mowed Stream Bank
Mowed stream banks offer a waterway no protection from incoming solar (shortwave) radiation, nor terrestrial forms of impairment including nutrient-rich stormwater runoff and silt.
      • REFLECTED SHORTWAVE RADIATION—known as albedo, reflected solar (shortwave) radiation is energy directed away from the earth’s surface before being absorbed.  A surface’s albedo value is basically determined by its color, black having little reflective value, white and silvery surfaces reflecting nearly all solar (shortwave) radiation away.  A surface with no reflective properties has an albedo value of 0, while a totally reflective surface has a value of 1.  Clean snow with a value of about 0.85 to 0.9 (85% to 90%) is a highly reflective surface; yellow snow isn’t as good.  A stream, river, or lake blanketed with ice and snow will absorb very little solar energy and will rely upon other heat flux processes to trigger a melt and thaw.  The surface of open water has a varying albedo value determined mostly by the angle of the sun.  Solar radiation striking the water’s surface at a low angle is mostly reflected away, while that originating at an angle closer to zenith is more readily absorbed.
Forested Stream
To avoid the heating effects of solar (shortwave) and atmospheric longwave radiation, coldwater and coolwater fishes require streams offering protection from full exposure to direct sunlight and cloud cover.  Runs and creeks flowing beneath a closed canopy of forest trees are shielded from 25% or more of incoming radiation and are thus able to better maintain thermal stability during the most vulnerable period of the year for temperature-sensitive fishes, May through October.
      • LONGWAVE RADIATION—Radiation in the longwave spectrum is composed of infrared waves at frequencies lower than those of the shortwave spectrum.  Longwave radiation, sometimes just called infrared radiation, is produced by the earth and its atmosphere and is propagated in all directions, day and night.  It warms mostly the lower atmosphere which in turn warms the earth’s surface including its waters.  Some longwave energy can even be radiated into the waterway from its own streambed—and the stream can return the favor.  Other forms of mass surrounding  a stream such as a rocky shoreline or a man-made structure such as bridge pier can trade longwave radiation with a waterway.  The effect of these latter exchanges is largely trivial and never rivals the heat flux transfer of warm to cold provided by  conduction.
Longwave radiation emissions slow as the temperature of the emitting mass decreases, just as they also increase with temperature of the mass.  Longwave radiation emissions therefore decrease with altitude along with the temperature of the water vapor, carbon dioxide, methane, and other gases that produce them.  As such, the highest reaches of the atmosphere have a greatly reduced capability of shedding longwave radiation into space.  At ground level, lakes, creeks, and streams receive their greatest dose of longwave radiation while beneath the cover of low-lying clouds or fog.  (NASA image)
      • CANOPY RADIATION—Trees emit longwave radiation that may have a limited heat flux impact on waterway temperature.  This radiation is diffuse, of scattered effect, and scarcely detectable, particularly beneath multilayered dense canopies.  Some of the infrared energy transmitted by the tree canopy is radiated skyward as well.
      • WATER RADIATION—Water, like all earthly matter composed of vibrating molecules, emits longwave radiation.  This heat flux process provides an ongoing cooling effect to streams, rivers, lakes, and oceans—warmer ones shedding infrared energy at a faster rate than those that are cold.

Now that we have a basic understanding of the heat flux processes responsible for determining the water temperatures of our creeks and rivers, let’s venture a look at a few graphics from gauge stations on some of the lower Susquehanna’s tributaries equipped with appropriate United States Geological Survey monitoring devices.  While the data from each of these stations is clearly noted to be provisional, it can still be used to generate comparative graphics showing basic trends in easy-to-monitor parameters like temperature and stream flow.

Each image is self-labeled and plots stream temperature in degrees Fahrenheit (bold blue) and stream discharge in cubic feet per second (thin blue).

The West Conewago Creek drains much of the Gettysburg Basin’s Triassic redbeds in Adams and northern York Counties in Pennsylvania and includes a small headwaters area in northern Maryland.  The gauge station is located just a over a mile upstream from the waterway’s mouth on the Susquehanna just below Conewago Falls.  Right through the summer heatwave, this 90-day graph shows a consistent daily pattern of daytime rises in temperature and nighttime cooling.  To the right, a rapid cool down can be seen coinciding with two periods of high water, the first from a series of heavy thundershowers, the second from flooding caused by the remnants of Hurricane Debby.  Notice that the early August downpours were so heavy that they cooled the hot surface runoff and waterway quickly, without creating a rise in stream temperature at the gauging station.  Had this monitoring device been located on a small tributary in an area with an abundance of impervious surfaces, there would probably have been a brief rise in stream temperature prior to the cooldown.  (United States Geological Survey image)

The daily oscillations in temperature reflect the influence of several heat flux processes.  During the day, solar (shortwave) radiation and convection from summer air, especially those hot south winds, are largely responsible for the daily rises of about 5° F.  Longwave radiation has a round-the-clock influence—adding heat to the stream during the day and mostly shedding it at night.  Atmospheric exchange including evaporative cooling may help moderate the rise in stream temperatures during the day, and certainly plays a role in bringing them back down after sunset.  Along its course this summer, the West Conewago Creek absorbed enough heat to render it a warmwater fishery in the area of the gauging station.  The West Conewago is a shallow, low gradient stream over almost its entire course.  Its waters move very slowly, thus extending their exposure time to radiated heat flux and reducing the benefit of cooling by atmospheric exchange.  Fortunately for bass, catfish, and sunfish, these temperatures are in the ideal range for warmwater fishes to feed, grow, and reproduce—generally over 80° F, and ideally in the 70° to 85° F range.  Coolwater fishes though, would not find this stream segment favorable.  It was consistently above the 80° F maximum and the 60° to 70° F range preferred by these species.  And coldwater fishes, well, they wouldn’t be caught dead in this stream segment.  Wait, scratch that—the only way they would be caught in this segment is dead.  No trouts or sculpins here.

The Codorus Creek drains primarily the carbonate valleys of York County to the south of the West Conewago watershed.  This gauge station is located about a mile upstream from the creek’s mouth on the Susquehanna just below Haldeman Riffles.  The graphic pattern is very similar to that of the West Conewago’s: daily heating and cooling cycles and a noticeable drop in stream temperature in early August caused by a day of thundershowers followed by the remnants of Hurricane Debby.  (United States Geological Survey image)

Look closely and you’ll notice that although the temperature pattern on this chart closely resembles that of the West Conewago’s, the readings average about 5 degrees cooler.  This may seem surprising when one realizes that the Codorus follows a channelized path through the heart of York City and its urbanized suburbs—a heat island of significance to a stream this size.  Before that it passes through numerous impoundments where its waters are exposed to the full energy of the sun.  The tempering factor for the Codorus is its baseflow.  Despite draining a smaller watershed than its neighbor to the north, the Codorus’s baseflow (low flow between periods of rain) was 96 cubic feet per second on August 5th, nearly twice that of the West Conewago (51.1 cubic feet per second on August 5th).  Thus, the incoming heat energy was distributed over a greater mass in the Codorus and had a reduced impact on its temperature.  Though the Codorus is certainly a warmwater fishery in its lower reaches, coolwater and transitional fishes could probably inhabit its tributaries in segments located closer to groundwater sources without stress.  Several streams in its upper reaches are in fact classified as trout-stocked fisheries.

This is a zoomed-in look at the previous graph showing the impact of a rainfall event on the water temperatures in Codorus Creek.  Unlike the sharp declines accompanying the deluge of flood waters during the two events in early August, these lesser storms in late June generated just enough runoff to capture heat energy from impervious surfaces and warm the creek, temporarily breaking the daily heating/cooling cycle.  Upstream in the immediate area of the runoff, the impact on the stream and/or its tributaries was probably much more dramatic, certainly raising temperatures into the nineties or above.  (United States Geological Survey image)
Kreutz Creek drains a carbonate bedrock area of York County and flows parallel to the Lincoln Highway (US 30) to enter the Susquehanna at Wrightsville.  The gauging station is about one mile upstream from the creek’s mouth.   (United States Geological Survey image)

The Kreutz Creek gauge shows temperature patterns similar to those in the West Conewago and Codorus data sets, but notice the lower overall temperature trend and the flow.  Kreutz Creek is a much smaller stream than the other two, with a flow averaging less than one tenth that of the West Conewago and about one twentieth of that in the Codorus.  And most of the watershed is cropland or urban/suburban space.  Yet, the stream remains below 80° F through most of the summer.  The saving graces in Kreutz Creek are reduced exposure time and gradient.  The waters of Kreutz Creek tumble their way through a small watershed to enter the Susquehanna within twenty-four hours, barely time to go through a single daily heating and cooling cycle.  As a result, their is no chance for water to accumulate radiant and convective heat over multiple summer days.  The daily oscillations in temperature are less amplified than we find in the previous streams—a swing of about three degrees compared to five.  This indicates a better balance between heat flux processes that raise temperature and those that reduce it.  Atmospheric exchange in the stream’s riffles, forest cover, and good hyporheic exchange along its course could all be tempering factors in Kreutz Creek.  From a temperature perspective, Kreutz Creek provides suitable waters for coolwater fishes.

Muddy Creek drains portions of southern York County through rolling farmland and woodlots.  There are no large impoundments or widespread urban impacts in the watershed, which may help explain its slightly lower temperature trends.  (United States Geological Survey image)

Muddy Creek is a trout-stocked fishery, but it cannot sustain coldwater species through the summer heat.  Though temperatures in Muddy Creek may be suitable for coolwater fishes, silt, nutrients, low dissolved oxygen, and other factors could easily render it strictly a warmwater fishery, inhabited by species tolerant of significant stream impairment.

Chiques Creek drains mostly limestone farmland in northwestern Lancaster County.  The gauging station is located near the stream’s mouth on the Susquehanna at Chiques (Chickies) Rock.  Oscillations in temperature again resemble the other waterways, but daily highs remain almost entirely below 80 degrees.  (United States Geological Survey image)

A significant number of stream segments in the Chiques watershed have been rehabilitated to eliminate intrusion by grazing livestock, cropland runoff, and other sources of impairment.  Through partnerships between a local group of watershed volunteers and landowners, one tributary, Donegal Creek, has seen riparian buffers, exclusion fencing, and other water quality and habitat improvements installed along nearly ever inch of its run from Donegal Springs through high-intensity farmland to its mouth on the main stem of the Chiques just above its confluence with the Susquehanna.  The improved water quality parameters in the Donegal support native coldwater sculpins and an introduced population of reproducing Brown Trout.  While coldwater habitat is limited to the Donegal, the main stem of the Chiques and its largest tributary, the Little Chiques Creek, both provide suitable temperatures for coolwater fishes.

Limestone Formation on Little Chiques Creek
Streams in the Chiques Creek and similar limestone watersheds often pass through areas with significant bedrock formations.  Heat flux processes including groundwater input, hyporheic exchange, and streambed conductive exchange can have a greater influence on water temperature along these segments.
Eastern Blacknose Dace
A breeding condition Eastern Balcknose Dace, one of the coldwater transition fishes found in the Chiques and its tributaries.
Common Shiner
The Common Shiner (Luxilus cornutus), a fish tolerant of warmwater streams, prefers cool, clear waters for spawning.  For protection from late-spring and summer heat, breeding males may seek a section of creek with a streambed inflow of limestone groundwater to defend as their nesting territory.
A closeup of the Chiques Creek graph showing what appears to be a little bump in temperature caused by surface runoff during a couple of late-May showers.  Stream rehabilitation is an ongoing process and the pressures of land disturbances both old and new present challenges to those who make it their passion to fix the wrongs that have been inflicted upon our local waters.  Even the  exemplary Donegal Creek faces new threats from urbanization in one of its headwater areas several miles to the northwest of the historic springs.  (United States Geological Survey image)
Conewago Creek (East) drains primarily Triassic redbed farmlands in Dauphin, Lancaster, and Lebanon Counties.  Much of the headwaters area is forested but is experiencing an increasing rate of encroachment by housing and some commercial development.  Conewago Creek (East) enters the Susquehanna on the east side of Conewago Falls at Three Mile Island.  The watershed is equipped with three U.S.G.S. gauge stations capable of providing temperature data.  This first one is located just over a mile upstream of the creek’s mouth.  (United States Geological Survey image)

Despite its meander through and receipt of water from high-intensity farmland, the temperature of the lower Conewago (East) maxes out at about 85° F, making it ideal for warmwater fishes and even those species that are often considered coolwater transition fishes like introduced Smallmouth Bass, Rock Bass, Walleye, and native Margined Madtom.  This survivable temperature is a testament to the naturally occurring and planted forest buffers along much of the stream’s course, particularly on its main stem.  But the Conewago suffers serious baseflow problems compared to other streams we’ve looked at so far.  Just prior to the early August storms, flow was well below 10 cubic feet per second for a drainage area of more than fifty square miles.  While some of this reduced flow is the result of evaporation, much of it is anthropogenic in origin as the rate of groundwater removal continues to increase  and a recent surge in stream withdraws for irrigation reaches its peak during the hottest days of summer.

Juvenile Rock Bass
A juvenile Rock Bass.
A juvenile Margined Madtom.
A juvenile Margined Madtom.
A closer look at the Conewago Creek (East) graphic shows the temperature drop associated with a series of thundershowers and the remnants of Hurricane Debby in early August.  Despite the baseflow being below five cubic feet per second, the cooling effect of the downpours as measured in the area of the gauge was significant enough to overwhelm any heating of runoff that may have occurred as precipitation drained across hardened soils or man-made impervious surfaces.  (United States Geological Survey image)

A little side note—the flow rate on the Conewago at the Falmouth gauge climbed to about 160 cubic feet per second as a result of the remnants of Hurricane Debby while the gauge on the West Conewago at Manchester skyrocketed to about 20,000 cubic feet per second.  Although the West Conewago’s watershed (drainage area) is larger than that of the Conewago on the east shore, it’s larger only by a multiple of two or three, not 125.  That’s a dramatic difference in rainfall!

The Bellaire monitoring station on Conewago Creek (East) is located on the stream’s main stem just downstream from the mouth of Little Conewago Creek, a tributary with its origins in farmland and woodlots.  (United States Geological Survey image)

The temperatures at the Bellaire monitoring station, which is located upstream of the Conewago’s halfway point between its headwaters in Mount Gretna and its mouth, are quite comparable to those at the Falmouth gauge.  Although a comparison between these two sets of data indicate a low net increase in heat absorption along the stream’s course between the two points, it also suggests sources of significant warming upstream in the areas between the Bellaire gauge and the headwaters.

Data from the gauge site on the Little Conewago Creek shows a temperature averaging about five degrees cooler than the gauge several miles downstream on the main stem of the Conewago at Bellaire.  (United States Geological Survey image)

The waters of the Little Conewago are protected within planted riparian buffers and mature woodland along much of their course to the confluence with the Conewago’s main stem just upstream of Bellaire.  This tributary certainly isn’t responsible for raising the temperature of the creek, but is instead probably helping to cool it with what little flow it has.

Juvenile Eastern Blacknose Dace (top) and a juvenile Longnose Dace.
A stream like the Little Conewago Creek with daily temperatures that remain mostly below 80 degrees and retreat to 75 degrees or less during the night can be suitable for coldwater transition fishes like these juvenile Eastern Blacknose Dace (top) and Longnose Dace.

Though mostly passing through natural and planted forest buffers above its confluence with the Little Conewago, the main stem’s critically low baseflow makes it particularly susceptible to heat flux processes that raise stream temperatures in segments within the two or three large agricultural properties where owners have opted not to participate in partnerships to rehabilitate the waterway.  The headwaters area, while largely within Pennsylvania State Game Lands, is interspersed with growing residential communities where potable water is sourced from hundreds of private and community wells—every one of them removing groundwater and contributing to the diminishing baseflow of the creek.  Some of that water is discharged into the stream after treatment at the two municipal sewer plants in the upper Conewago.  This effluent can become quite warm during processing and may have significant thermal impact when the stream is at a reduced rate of flow.  A sizeable headwaters lake is seasonally flooded for recreation in Mount Gretna.  Such lakes can function as effective mid-day collectors of solar (shortwave) radiation that both warms the water and expedites atmospheric exchange.

The Conewago Creek (East) Watershed from the Bellaire U.S.G.S. Gauging Station (lower left) upstream to the headwaters in Mount Gretna.  (United States Geological Survey image)

Though Conewago Creek (East) is classified as a trout-stocked fishery in its upper reaches in Lebanon County, its low baseflow and susceptibility to warming render it inhospitable to these coldwater fishes by late-spring/early summer.

River Chub
Despite being considered a warmwater fish, the River Chub (Nocomis micropogon) will ascend streams like the Conewago to seek cooler, gravel-bottomed waters for spawning.  Reduced baseflow has probably rendered the stream currently too small for this species on Pennsylvania State Game Lands in Colebrook where this specimen was photographed in 2018.
Juvenile Golden Shiner
The Golden Shiner, another warmwater fish, often ascends streams to enter cooler water. Juvenile Golden Shiners like this one will move into shallower headwaters not only to seek reduced temperatures, but to escape large predatory fishes as well.
Irrigation using stream water.
Irrigation of agricultural fields using a large portion of the already diminished baseflow in the Conewago Creek (East) just downstream of the Bellaire gauging station.  Despite millions of dollars in investment to rehabilitate this Susquehanna valley stream, the riparian buffers and other practices can have little effect when the creek gets sucked down to just a trickle.  Low baseflow is a hard nut to crack.  It’s best prevented, not corrected.
Hammer Creek, a trout-stocked fishery, originates, in part, within Triassic conglomerate in the Furnace Hills of Lebanon County, then flows north into the limestone Lebanon Valley where it picks up significant flow from other tributaries before working its way south back through the Furnace Hills into the limestone farmlands of Lancaster County.  From there the stream merges with the Cocalico Creek, then the Conestoga River, and at last the Susquehanna.  Note the tremendous daily temperature oscillations on this headwaters stream as it surges about 15 degrees each day before recovering back close to groundwater temperature by sunrise the next day.  (United States Geological Survey image)
Headwaters of Hammer Creek including Buffalo Springs, a significant source of cold groundwater feeding the western leg of the stream.  The large dams on this section that created the Lebanon and Rexmont Reservoirs have been removed.  (United States Geological Survey base image)

The removal of two water supply dams on the headwaters of Hammer Creek at Rexmont eliminated a large source of temperature fluctuation on the waterway, but did little to address the stream’s exposure to radiant and convective heat flux processes as it meanders largely unprotected out of the forest cover of Pennsylvania State Game Lands and through high-intensity farmlands in the Lebanon Valley.  Moderating the temperature to a large degree is the influx of karst water from Buffalo Springs, located about two miles upstream from this gauging station, and other limestone springs that feed tributaries which enter the Hammer from the east and north.  Despite the cold water, the impact of the stream’s nearly total exposure to radiative and other warming heat flux processes can readily be seen in the graphic.  Though still a coldwater fishery by temperature standards, it is rather obvious that rapid heating and other forms of impairment await these waters as they continue flowing through segments with few best management practices in place for mitigating pollutants.  By the time Hammer Creek passes back through the Furnace Hills and Pennsylvania State Game Lands, it is leaning toward classification as a coolwater fishery with significant accumulations of sediment and nutrients.  But this creek has a lot going for it—mainly, sources of cold water.  A core group of enthusiastic landowners could begin implementing the best management practices and undertaking the necessary water quality improvement projects that could turn this stream around and make it a coldwater treasure.  An organized effort is currently underway to do just that.  Visit Trout Unlimited’s Don Fritchey Chapter and Donegal Chapter to learn more.  Better yet, join them as a volunteer or cooperating landowner!

Male Creek Chub
The male Creek Chub, one of our coolwater fishes, develops head tubercles and becomes flushed with color during spawning season.  Hammer Creek not only provides a home for the Creek Chub, its cold headwaters provide refuge for a population of native Brook Trout too.
Like no other example we’ve looked at so far, this closeup of the Hammer Creek graphic shows temperature bumps correlating with the stormwater runoff from early August’s rains.  Because the stream flow is small and the precipitation rate was not as great at this location, the effect of heat flux from runoff is more readily apparent.  (United States Geological Survey image)
Brook Trout adult and juvenile.  (United States Fish and Wildlife Service image by Ryan Hagerty)

For coldwater fishes, the thousands of years since the most recent glacial maximum have seen their range slowly contract from nearly the entirety of the once much larger Susquehanna watershed to the headwaters of only our most pristine streams.  Through no fault of their own, they had the misfortune of bad timing—humans arrived and found coldwater streams and the groundwater that feeds them to their liking.  Some of the later arrivals even built their houses right on top of the best-flowing springs.  Today, populations of these fishes in the region we presently call the Lower Susquehanna River Watershed are seriously disconnected and the prospect for survival of these species here is not good.  Stream rehabilitation, groundwater management, and better civil planning and land/water stewardship are the only way coldwater fishes, and very possibly coolwater fishes as well, will survive.  For some streams like Hammer Creek, it’s not too late to make spectacular things happen.  It mostly requires a cadre of citizens, local government, project specialists, and especially stakeholders to step up and be willing to remain focused upon project goals so that the many years of work required to turn a failing stream around can lead to success.

Riparian Buffer
Riparian buffers with fences to exclude livestock can immediately begin improving water quality.  With establishment of such vegetative buffers, the effects of stressors that otherwise eliminate coldwater and coolwater fishes from these segments will begin to diminish.
Riparian Buffer
Within five to ten years, a riparian buffer planted with native trees is not only helping to reduce nutrient and sediment loads in the stream, it is also shielding the waters from heat flux processes including the solar (shortwave) radiation that raises water temperatures to levels not tolerated by coldwater and coolwater fishes.
Riparian Buffer
A well-established riparian buffer.
Forested Stream
A forested stream.

You’re probably glad this look at heat flux processes in streams has at last come to an end.  That’s good, because we’ve got a lot of work to do.

Add one more benefit to the wildflower meadow, it infiltrates stormwater to recharge the aquifer much better than mowed grass.  And another related plus, it reduces runoff and its thermal pollution.  Besides, you don’t have time to mow grass, because we have work to do!
Potomac Sculpin
Our native coldwater fishes including the Potomac Sculpin will survive only if we protect and expand the scattered few habitats where they have taken refuge.  They have no choice but to live in these seriously threatened places, but we do.  So let’s give ’em some space.  How ’bout it?  (United States Fish and Wildlife Service image by Ryan Hagerty)

Photo of the Day

Berries and foliage of the Black Gum, also known as the Black Tupelo.
In the forests and woodlots of the lower Susquehanna watershed, the Black Gum, also known as the Black Tupelo, is always the first of our native trees to pop with autumn color.  Its crimson leaves glow in an otherwise green landscape to help lure hungry birds including waxwings, American Robins, and Pileated Woodpeckers to its soon-to-be-ripe berries.  The seeds contained in the fruit are thus well-distributed as a by-product of this avian feast.  While not among the most massive of our trees, the Black Gum can live for over five hundred years, an age not exceeded by any other non-clonal indigenous flowering plant.

Wildflower Meadow Update

Do you recall our “Photo of the Day” from seven months ago…

Riverfront Park Wildflower Meadow
Here’s something to look forward to in the new year.  The good citizens of East Donegal Township in Lancaster County have partnered with Alliance for the Chesapeake Bay to establish an extensive wildflower meadow on what had been a mowed field of turf grass at Riverside Park in the Susquehanna floodplain near Marietta.  As the photo shows, the lawn plants have been eliminated in preparation for seeding with a diverse assortment of native grasses and wildflowers to provide habitat for birds and pollinators including butterflies, bees, and other insects.  Once established, the meadow’s extensive vegetative growth will help reduce stormwater runoff by better infiltrating rainfall to recharge the aquifer.  During flood events, the plantings will provide soil stabilization and increase the ability of the acreage to uptake nutrients, thus reducing the negative impact of major storms on the quality of water in the river and in Chesapeake Bay.  Check the project’s progress by stopping by from time to time in 2024!

Well, here’s what that site looks like today…

Riverfront Park Wildflower Meadow
The wildflowers, thousands of them, are now in bloom!
Riverfront Park Wildflower Meadow
Black-eyed Susan and Blue Vervain (Verbena hastata) dominate the assortment currently in flower.

And there are pollinating insects galore, most notably butterflies…

Cabbage White
A Cabbage White collecting nectar on Blue Vervain.
A Sulphur
A Clouded or Orange Sulphur among the grasses in the meadow.
Silver-spotted Skipper
A Silver-spotted Skipper.
Least Skipper
The Least Skipper is our tiniest butterfly.
Little Glassywing
The Little Glassywing (Vernia verna), this one feeding on vervain nectar, deposits its eggs on Purpletop grass, which then functions as the host plant for this butterfly’s larvae.
Summer Azure
A Summer Azure (Celastrina neglecta) feeding on the nectar of a Black-eyed Susan.
Common Buckeye
A Common Buckeye on a “Gloriosa Daisy”, a showy, large-flowered cultivar of Black-eyed Susan.
Red-winged Blackbird
A Red-winged Blackbird with a caterpillar found among the meadow’s lush growth.
Tiger Swallowtail
An Eastern Tiger Swallowtail on Blue Vervain.  Nearby Yellow (Tulip) Poplars and other trees serve as host plants for this butterfly’s larvae.
Black Morph Eastern Tiger Swallowtail
The black morph of the Eastern Tiger Swallowtail shows subdued shading in the wings that closely resembles the brilliant color patterns of the more familiar yellow form.
Sachem
The Sachem, this one visiting a Black-eyed Susan, is a variable species with a range that normally lies south of the 40th parallel, the line of latitude that intersects the Susquehanna in the area of the Conejohela Flats at Washington Boro.
A Sachem visiting the blooms of Oxeye sunflower.   During recent weeks, scorching winds from the south and southwest have transported an abundance of these vagrant skippers into the lower Susquehanna valley and beyond.
Sachem
A male Sachem approaching the bloom of a “Gloriosa Daisy”.  Miles north of the 40th parallel, wandering Sachems are currently the most numerous of the butterflies at the Riverfront Park wildflower meadow.
Partridge Pea
Here and there among the meadow’s plantings we noticed one of our favorites starting to flower, the Partridge Pea.
Cloudless Sulphur
Partridge Pea happens to be a host plant for another vagrant from the south, the big, lime-yellow Cloudless Sulphur.  We saw at least half a dozen patrolling the meadow.
Zebra Swallowtail
The stars of the show are the Zebra Swallowtails, gorgeous butterflies that rely on stands of native Common Paw-paw trees in the river floodplain to host their eggs and larvae.
Zebra Swallowtail
The red-white-and-blue underside of a Zebra Swallowtail.
Zebra Swallowtail
WOW!

Why on earth would anyone waste their time, energy, and money mowing grass when they could have this?  Won’t you please consider committing graminicide this fall?  That’s right, kill that lawn—at least the majority of it.  Then visit the Ernst Seed website, buy some “Native Northeast Wildlflower Mix” and/or other blends, and get your meadow planted in time for the 2025 growing season.  Just think of all the new kinds of native plants and animals you’ll be seeing.  It could change your life as well as theirs.

Snowberry Clearwing
A Snowberry Clearwing (Hemaris diffinis), more commonly known as a hummingbird moth, visits the flowers of Blue Vervain in the Riverfront Park wildflower meadow.