Migrating Waterfowl on Lotic Fresh Waters

Lotic vs. Lentic Freshwater Ecosystems — Some comparative attributes of unspoiled lotic vs. lentic freshwater ecosystems. Low-gradient (slow-moving) lotic waters often create, and remain connected to, accompanying riverine wetlands (a lentic freshwater ecosystem). These swamps, marshes, and ditches absorb, purify, and infiltrate flood waters while supporting a diverse number of plant and animal species.

We frequently perceive all waterfowl migration to be synchronized with the conspicuous movements of familiar species like Snow Geese, Tundra Swans, and Canada Geese—big flights coming south in October and November, then a return to the north in late February and March. And we’re all quite aware of the occurrence of large gatherings of some of these migrants while they make stopovers on some of our largest lentic (still) waters—the man-made lakes and reservoirs created by damming local streams. But did you know that there are populations of colorful waterfowl with dynamic migrations that extend throughout the winter and early spring with movements that are often continuous. Under favorable conditions, these birds favor the lotic (flowing) waters of the river and its larger tributaries as they transit the lower Susquehanna valley. That’s because unpolluted lotic freshwater ecosystems support a greater diversity of plants and animals than lentic waters, and therefore offer more opportunities for hungry migrating waterfowl to find food. Let’s have a look at some of the species that visit the river during their seasonal journeys…

Ice on the Susquehanna — While the urge to head south in the autumn is largely stimulated by the shortening of the photoperiod, it is the presence of ice, particularly on glacial lakes throughout the lands to the north of the lower Susquehanna River basin, that pushes many diving ducks to finally make their way south toward the guarantee of open-water feeding areas along the coast. This movement may occur at anytime between November and late February or, as we have seen during some of the mild winters of recent decades, it may scarcely be noticed at all.

Common Mergansers often lead they way when it comes to migratory diving ducks. They regularly move south in conspicuous numbers by late November and December and are regularly pushing north as soon as the ice begins to melt. During a typical year, it is not unusual for some populations of these large diving birds to remain north of us during the winter. Then, in the days after a sudden rush of frigid polar air, an appreciable increase in ice cover will force a mid-winter movement of birds down the Susquehanna.

Heat Flux Sources Impacting Temperature in Lotic Fresh Waters — Temperatures in lotic fresh waters vary over the length of the stream or river. They are largely determined by the collective impact of the numerous sources of heat flux depicted in this graphic. (Environmental Protection Agency image)

Buffleheads begin passing through the lower Susquehanna region in Novemeber on their way to coastal saltwater bays for the winter. Lingering populations feed by diving in the river’s pools and riffles for benthic invertebrates including snails and insect larvae. Lesser quantities of aquatic plant matter supplement their diet.

Many Common Goldeneyes will remain on shallow, ice-free waters of the northern lakes and rivers sculpted by the most recent glacial event, but only until they are forced south into and through the lower Susquehanna valley by the encroachment of freezing conditions. On the river, they are among the dozen or so species of diving ducks we see visiting or passing through during the typical late fall and early river.

Geomorphological Zonation of a Stream or River — During their visits to the lotic (also known as riverine) fresh waters of the Susquehanna and its largest tributaries, benthic-feeding waterfowl make short dives to take advantage of the plants, small fish, invertebrates, and other food sources inhabiting the stream bottom in the riffles and pools of the free-flowing waterway. Substrates, listed here by size (in descending order), along with other parameters influenced by this zonation determine the variety and abundance of the forage available to migrating waterfowl and other consumers. Ice or high water and poor visibility due to flooding can render the riffles and pools of the channel unusable for feeding. The birds must then choose to either linger and rest without feeding or leave the lotic freshwater habitat to seek sustenance. During a flood, this may require relocation to a nearby lentic (still) body of fresh water such as a lake or reservoir. The presence of ice will almost invariably force the birds to fly on to the Atlantic Coastal Plain and the tidal waters of its bays and estuaries.

Hooded Mergansers are one of the few species of diving ducks likely to utilize flooded shoreline timber and riverine (fluvial) wetlands as refuge from high water on Susquehanna.

Pied-billed Grebe and Canvasbacks — A Pied-billed Grebe and a pair of Canvasbacks on an ice-free stretch of the lower Susquehanna in mid-winter feed and loaf in a riffle-flanked pool where a large mat of American Eelgrass, a submerged aquatic plant also known as Tapegrass or Wild Celery, grows during the summer. The vast mosaic of riffles and pools in a river this size offers tremendous opportunities for a diverse array of aquatic species to find their niche wherein they can survive and flourish.

The presence of ice forces Buffleheads and other diving ducks to gather in turbulent open water, often below a riffle or dam. Another alternative is to continue on toward the salty bays and estuaries of the coast. High water may push these birds into the shallows among the flooded woods to feed, but they seldom utilize heavily forested riparian wetlands as a refuge due to their need for a running start to get airborne.

**Riffle and Pool Characteristics of High Gradient (A) and Low Gradient (B) Streams**. This graphic illustrates the change in deposition characteristics of a stream or river as its gradient decreases. A high-gradient stream (A) has a rapid velocity, often forms falls, and tends to carry away a high volume of all but the largest of particles of potential substrates as they erode from the surrounding landscape. On a low-gradient stream, the loss in water velocity reduces the water column’s ability to transport even the smallest of substrate particles. Deposition of this gravel, sand, silt, and clay forms lateral bars that over time create the familiar meandering path of a naturally flowing lowland stream. (National Park Service image)

Benthic Life in Lotic Freshwaters — Benthic substrates in lotic freshwater pools and riffles support an abundance of life forms ranging from colorful diatoms on rocks and cobble, to invertebrates including snails and insect larvae, to fishes like this young Channel Catfish. Free of accumulations of sediment, this river bottom not only provides habitat for a healthy fishery, it facilitates the bidirectional exchange of water between the Susquehanna and its underlying aquifer.

On the lower Susquehanna, populations of young Quillback suckers are found almost exclusively in clear, high-gradient pools.

The Harlequin Duck winters along the rocky shores and man-made jetties of the Atlantic coast. In summer, they nest on fast-moving, headwater streams well to our north. Very rare on the Susquehanna, this is the first of two individuals found during March and April of 2025. It was observed feeding in the swift waters of the high-gradient riffles and pools where the river cuts through Blue Mountain north of Harrisburg. During previous weeks, Harlequin Ducks were being seen along the coast as far south as the mouth of the Chesapeake at Cape Charles, Virginia. It’s very possible that some of these birds traveled north through the bay area and up the Susquehanna on their way north.

**Fluvial Geomorphology of a Stream**. Many of the Susquehanna’s tributaries pass through each of these three erosional zones. Along the way, they carry out the process of breaking down the mountains formed by the Allegheny orogeny, the collision of North America and Africa that created the supercontinent Pangea about 325 to 260 million years ago (during portions of both the Carboniferous and Permian periods). Today’s main stem of the lower Susquehanna passes through a transfer zone (Zone 2), carrying eroded materials to a depositional zone (Zone 3) located within the ancient Susquehanna canyon stretching from Havre de Grace, Maryland, to Norfolk Canyon on the edge of the continental shelf. Within this zone, more than a 10,000-year accumulation of post-glacial sediments lies submerged by the rising waters of the Atlantic Ocean and Chesapeake Bay. Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path has eroded passage through the highlands. (National Park Service image)

Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path continues to erode passage through the bedrock. On this 1908 map of the Susquehanna at Conewago Falls, alluvial terraces of gravel, sand, silt, and clay can readily been seen as pale areas nearly lacking brown contour lines along the shorelines and islands of the river. Deposits within most of these terraces date back to the melt period following the most recent glacial event and beyond. The delta shown at the mouth of Conewago Creek (west) includes massive volumes of material deposited by both the creek and the river. This delta is currently known as Brunner Island, much of it developed as the site of a coal/gas-fired electric generating station. Terrace deposits along the Susquehanna’s shorelines created extensive perched marshes and swamps (wooded marshes) fed by rains, high river water, small streams, and springs, the latter often seeping from the base of the rocky escarpments carved by the ancient Susquehanna and defining the present-day inland border of the floodplain. We call these sites “Alluvial Terrace Wetlands”. Few of these critical components of river morphology survive. Those not drained for farmland were obliterated by urbanization and canal, railroad, and highway construction. (United States Geological Survey base image: Middletown, PA, quadrangle, 1908)

Water Willow is a familiar emergent plant that colonizes lateral bars and other alluvial deposits in low-gradient segments of the Susquehanna.

Water Willow Roots — The fine roots of Water Willow collect sediment and absorb nutrients while creating dense cover for young fish and numerous species of invertebrates including the Virginian River Horn Snails seen here.

Prior to the nineteenth century, the low-gradient flow regime of the river both above and below the riffles at Chiques Rock (lower right on map) created prime wildlife habitat. The natural accumulations of nutrients and substrates carried into and through the lotic waterway’s pools and riffles were cycled into an ideal growing medium for extensive mats of American Eelgrass and other aquatic plants. This underwater forest hosted a seemingly endless abundance of invertebrates and fishes (both resident and migratory)—supporting a variety of consumer species including various populations of humans. But soon after the mass clearing of much of the watershed’s land for farming and lumber, the mill ponds created by dams constructed on streams to power saw and grain mills became brimful with sediments eroded from the unprotected ground. During storm events, torrents of these sediments then flowed full bore toward the Susquehanna, and began accumulating in the low-gradient segments of the river.

Legacy Sediments — Sediments left behind after the removal of mill dams are known as legacy sediments. They disconnect the stream from its historic floodplain and riverine (fluvial) wetlands, thus intensifying the impact of high water in the surrounding landscape. As these nutrient-charged deposits wash away, they become a source of pollution in the waters of the Susquehanna and Chesapeake.

A mat of American Eelgrass growing in the flowing waters of the Susquehanna below Conewago Falls. Eelgrass and other submerged aquatic plants provide essential habitat for a wide variety of small fish and invertebrates while also consuming nutrients deposited in the cobble, gravel, and sand substrate of the river’s pools. Excess quantities of smaller particles of silt and clay can clog the substrate and thus inhibit the hyporheic exchange of water between the stream channel and the underlying aquifer, often diminishing the biomass and diversity of organisms inhabiting this benthic habitat. Buried in these life-choking sediments, the river bottom becomes inhospitable to growth of submerged aquatics including eelgrass.

This low-gradient stretch of the Susquehanna at Marietta flows parallel to the Chickies Quartzite “Hellam Hills” before making a sharp right turn to punch through the ridge as a series of rapids at Chiques Rock. Formerly a fully functional lotic ecosystem and a paradise for migrating waterfowl, this river segment is now impaired by accumulations of nutrient-laden sediments from agricultural and urban runoff.

Conewago Falls Flood Waters — Nutrient and sediment-loaded flood waters roar across the diabase boulders at the York Haven Dam and Conewago Falls, a high-gradient segment of the Susquehanna.

Flood Waters at Haldeman Riffles — They continue past Brunner Island (left power plant stacks) and through Haldeman Riffles and the Shocks Mills Railroad Bridge…

Flooding on the Marietta Broads — …into the stretch of river known as the “Marietta broads” along the base of the Chickies Quartzite “Hellam Hills”. The low stream gradient here produces a slower current and increased deposition of sediments.

Susquehanna Flooding at Chiques Rock — As the flood surges through the riffle and pool complex at Chiques Rock, the high stream gradient maintains a velocity in the water column sufficient to keep additional sediments in suspension until they reach the low-gradient river segment just downstream at Washington Boro, site of a naturally occurring lateral bar area known as the Conejohela Flats. These bars now lie within the man-made depositional zone known as “Lake Clarke”. Created nearly a century ago by construction of the Safe Harbor Dam, this impoundment is accumulating astounding volumes of nutrient-loaded sediments that continue to encapsulate the flats within a stream-impairing delta.

Redheads, Canvasbacks, and a Horned Grebe — Anytime from November to April on the lower Susquehanna, a group of Redheads, Canvasbacks (3 birds to right of the middle of the picture), and a Horned Grebe (lower left) is a welcome sight in a riverine pool known to have a summertime growth of American Eelgrass. Noted Dr. Herbert Beck in 1924 when describing the Canvasback, “Like all ducks, …, it stops to feed within the county (Lancaster) less frequently than formerly, principally because the vast beds of wild celery which existed earlier on broads of the Susquehanna, as at Marietta and Washington Borough, have now been almost entirely wiped out by sedimentation of culm. Prior to 1875 the four or five square miles of quiet water off Marietta were often as abundantly spread with wild fowl as the Susquehanna Flats are now. Sometimes there were as many as 500,000 ducks of various kinds on the Marietta broad at one time.”

Aythya genus ducks. — Today, seeing just dozens of Aythya genus ducks (Redheads, Canvasbacks, scaup) on the lower Susquehanna is a notable event. If they happen to be forced down by inclement weather while migrating through, you might get lucky enough to see several hundred.

During the past two centuries, as food supplies in the Susquehanna grew increasingly compromised for benthic feeders like these Lesser Scaup and other diving ducks, a change in distribution was necessary for survival.

Lesser Scaup in flight. — As individual species, Lesser Scaup and other waterfowl that fail to adapt to natural or man-made changes in their habitats and food supplies may see their overall global numbers falter.

Despite being located in the transfer zone, the lower Susquehanna has become a significant depositional zone along much of its length, mostly courtesy of the placement of sediment-trapping man-made dams.

Following construction of the mill dams and ponds on nearly every mile of the lower Susquehanna’s low-gradient tributary streams, enterprising parties moved on to the river. The first significant spans were constructed using wide timber cribs filled with large rock. They were placed to create water deep enough to allow canal boats to cross the Susquehanna at both Clark’s Ferry at the mouth of the Juniata River in Dauphin County and at Columbia/Wrightsville. These dams also diverted water into the newly excavated canals—the Pennsylvania Eastern Division Canal (completed in 1833) which followed the river’s east shore from Clark’s Ferry to Columbia, and the Susquehanna and Tidewater Canal (completed in 1840) along the west shore from Wrightsville to Havre de Grace, Maryland. Placement of these sediment-trapping man-made dams began a process of converting vast mileage of the lower Susquehanna from a transfer zone into a deposition zone. In addition, layout of the canals and locks followed the contours along the base of the riverside ridges, seriously altering most of the alluvial terrace wetlands that the river had created as a feature of its floodplain during the post-glacial period.

Construction of the canal dams was just the beginning. During the twentieth century, more massive dams would be added to the main stem of the river for hydroelectric energy production at York Haven, Safe Harbor, Holtwood, and Conowingo. Upon their completion, the days of unassisted anadromous fish migrations were over. On both the river and its tributaries, smaller dams including dangerous low-head dams maintain water levels for boating and recreation. They too create current-diminishing, pseudo-lentic waters that blanket the lotic riffle and pool substrates with polluted sediments.

MAN-MADE DAMS TURN LOTIC WATERS INTO UNFLUSHED TOILETS

Sediment Deposition Behind Lower Susquehanna Dams — The construction of dams on the lower Susquehanna has converted vast mileage of the river from a lotic freshwater system into a series of man-made lentic freshwater lakes. These areas have lost their function as a lotic transfer zone and are now a sort of dysfunctional series of depositional zones collecting vast volumes of sediment containing nutrients and other pollutants. Within each impoundment, the reduced velocity of the river causes it to drop suspended sand first, then the finer particles of silt and clay closer to the dam. The flow regime of riffles and pools is lost and the hyporheic zone that exchanges water between the river and the underlying aquifer is clogged. These impaired segments of river become ripe for eutrophication: algal blooms followed by die offs that can lead to a fatal reduction of dissolved oxygen in the water column.

Deposits of lateral bars of sediment in low-gradient segments of the Susquehanna can create shallow water feeding habitat for puddle/dabbling ducks like these Gadwall. Where sediment pollution is severe, benthic foods in these areas often consist mostly of invertebrates and plant matter deposited by the current, the buried substrates devoid of a functioning ecosystem and the waters subject to eutrophication.

Common Goldeneyes on a patch of open water on an otherwise ice-covered “Lake Clarke”, the impoundment created by Safe Harbor Dam. While they may find this spot advantageous for loafing, the food supply over the sediment-buried substrate will be limited.

By the end of the twentieth century, accumulations of polluted sediments behind lower Susquehanna dams were nearing capacity. There is no working plan to attenuate the massive release of these pollutants that may be triggered by a catastrophic flood. The effort to reduce nutrient and sediment runoff remains the focus so that new loading is kept to a minimum and won’t add to the capacity problems at the dams or continue downriver to the Chesapeake at full strength when the dams are full. Alleviating the sediment aggregation problem within the river’s impoundments is a tall order and a dilemma not easily solved. (United States Geological Survey image)

Fortunately for everything else living in the benthos, Common Mergansers are big enough to devour invasive, non-native Rusty Crayfish when they find them in our lotic waterways.

TIME TO CLEAN UP OUR ACT

WHERE DOES YOUR STORMWATER GO?

Channelized Urban Stream — **Channelized Urban/Suburban Streams Function as Sewers.** They have no attached lowlands or floodplains to absorb, purify, and infiltrate runoff from rain events. Pollutants including litter, pet waste, lawn chemicals, tire-wear particles, hazardous fluids, and sometimes untreated human excrement flush unchecked from the municipal storm drainage system into the waterway. Thermal shock from summer downpours washing across sun-heated pavements can kill temperature sensitive fishes and other aquatic life. Nutrient and sediment loads from these impaired tributaries later accumulate downstream in low-gradient segments of the Susquehanna, turning the river into an open-air cesspool. Aggressively working to implement projects that eliminate these sources of pollution are the only effective way to keep the problem from getting worse. Making things better requires a lot more dedication and effort. (United States Geological Survey image by Frank Ippolito)

RIPARIAN BUFFERS MAKE A DIFFERENCE…WIDER IS BETTER

FLOODPLAIN RESTORATION

Regardless OF HOW LONG YOU’VE BEEN CONDITIONED TO THINK OTHERWISE, THIS IS A DYSFUNCTIONAL, POLLUTED CREEK—AND IT NEEDS HELP

RESTORED TO ITS HISTORIC FUNCTIONS

Floodplain and Stream Restoration — On an adjacent segment of the same creek, this legacy sediment removal project restored a braided meandering channel and connected it to its newly liberated, historic floodplain. In just their second year, the fluvial wetlands are effectively absorbing stormwater and sequestering nutrients as an attached component of the stream’s riffle and pool complex. During our visit earlier this week, we found American Toads, Northern Leopard Frogs (Lithobates pipiens), and Northern Spring Peepers breeding here. It’s just as Castor canadensis would have it!

“STOP HEMMING AND HAWING AROUND ALREADY”

“HEY COWBOY, HOW ‘BOUT GETTIN’ THEM FILTHY LITTLE DOGIES OUTTA DAT CRICK?”

Impaired Stream — Here’s a polluted stream in a pasture with grazing livestock. The site is a former mill pond within which the creek eroded a channel following removal of the dam. The animals defecate and urinate where access to water is gained at a broken down embankment of the nutrient-loaded legacy sediments deposited in the pond more than a century ago. It’s a haphazard form of animal husbandry and a reminder that all it takes is just one stubborn jackass to foul up the whole waterway.

DIRECT SOURCES OF NITROGEN (AMMONIA) POLLUTION IN STREAMS

DID YOU KNOW that a dairy cow produces about 80 pounds of waste (excrement and urine) every day?

DID YOU KNOW that a horse produces about 50 pounds of waste (excrement and urine) every day?

DID YOU KNOW that a human produces about 3 to 4 pounds of waste (excrement and urine) every day? The exceptions, of course, are those who continue to insist that raising farm animals in and alongside a body of water is okey-doke—a harmless practice. These individuals tend to retain the former constituent of human waste and are thus full of it.

“ATTABOY TEX, THAT’S MORE LIKE IT!”

Stream Fencing and Livestock Crossing — Now that’s better. Legacy sediments have been removed to reconnect the stream to its floodplain. A livestock crossing and exclusion fencing has been installed, and a nutrient-consuming riparian buffer has been planted. This creek segment’s pollution woes have been mitigated. Do you have a neighbor needing this type of remedial work on their farm? Have them call your local conservation district office for advice. Some programs include financial assistance covering the costs of installation as well as monetary incentives for helping to clean up the water.

AND FINALLY

WHEN IT COMES TO BUILDING DAMS ON LOTIC FRESH WATERS…

…LEAVE IT TO THE BEAVERS

North American Beavers (Castor canadensis) create habitats that connect the riffle and pool regime of a low-gradient stream to a surrounding fluvial wetland that retains sediments, cycles nutrients, and provides essential habitat for hundreds of plant and animal species. Floodplains are for flooding. And if a beaver floods an area, you can be guaranteed that it was already part of a floodplain. You see, beavers don’t encroach upon humans, it’s humans doing the encroaching upon beavers. (National Park Service image)

MAD HATTERS

DID YOU KNOW that even before the landscape was cleared for farms and a supply of timber, and before mill dams on local creeks began accumulating soil runoff from the consequently barren hillsides, all the North American Beavers, the keystone species of lower Susquehanna stream ecology, were killed and sold to make hats? It’s no wonder things are fubar!

COMING SOON…

Horned Grebes are regular migrants and sometimes winter residents on ice-free stretches of the lower Susquehanna. They spend their time plying the benthic substrate of the river’s clear riffles and pools for a variety of invertebrates and small fish. Look for them moving north in coming days sporting this beautiful breeding plumage.

April and early May are prime time for observing Common Loons on the Susquehanna as they undertake a journey from the Atlantic surf where they spent the winter to nesting sites on northern lakes. For this migrant in breeding plumage, clear water for sighting plenty of benthic life in the river’s riffles and pools assures a successful dive in search of energy-replenishing forage.

April 15, 2025March 31, 2026

Coastal Waterfowl at the Capital City

In early April of each year, we like to take a dreary-day stroll along the Susquehanna in Harrisburg to see if any waterfowl or seabirds have dropped in for a layover before continuing their journey from wintering waters along the Atlantic seaboard to breeding areas well to our north and northwest. As showers started to subside this Saturday morning past, here are some of the travelers we had the chance to see…

Mixed flock of scaup species. — Hundreds of scaup were feeding at mid-river. To remain in suitable foraging habitat, the group is seen here flying upstream to the area of the Governor’s Mansion where they would commence yet another drift downstream to Independence Island before again repositioning to a favorable spot.

Lesser and Greater Scaup — By far, the majority of the ducks in this flock were Lesser Scaup showing white inner margins of the secondary flight feathers and more grayish margins in the primaries. Several Greater Scaup, including the one denoted by the hairline in this image, could be detected by the presence of bright white margins not only in the secondary flight feathers, but extending through the primaries as well.

Male Harlequin Duck — Harlequin Ducks (Histrionicus histrionicus) spend the summer nesting on turbulent high-gradient streams in Canada and Greenland. They mostly winter along rocky coastlines as far south as New England, but have adapted to feeding along man-made rock jetties in coastal New York and New Jersey. This winter, they were seen along jetties and sea walls at least as far south as Cape Charles, Virginia, and the mouth of Chesapeake Bay. During the past month, at least two Harlequin Ducks, including this male seen in flight on Saturday, have appeared on the river in the Harrisburg area, possibly as strays from this year’s wintering population at the mouth of the bay. These ducks are very rare habitat specialists, possibly (according to Behrens and Cox, 2013) numbering less than 1,500 birds along the entire east coast.

If you want a chance to see these seldom-observed visitors to the lower Susquehanna at Pennsylvania’s capital city, try a morning walk along mid-town’s Riverfront Park from Maclay Street to Forster Street. Also, try a stroll on City Island, particularly to the beach at the north end where you have a view of the mid-river areas upstream. To have better afternoon light, try the river’s west shore along Front Street in Wormleysburg from the Market Street Bridge upstream to Conodoguinet Creek. Once there, be certain to check the river from the Pennsylvania Fish and Boat Commission’s West Fairview Access Area at the mouth of the creek. And don’t be afraid to visit on a gloomy day; you never know what you might find!

Don’t forget to check the trees along the river shoreline where early stonefly hatches can often attract hungry insectivores. We found this and six other Eastern Phoebes crowded into the trees at water’s edge just upriver from the Governor’s Mansion during Saturday’s migrant fallout.

SOURCES

Behrens, Ken, and Cameron Cox. 2013. Seawatching: Eastern Waterbirds in Flight. Houghton Mifflin Harcourt Publishing Company. New York, NY.

May 13, 2024May 14, 2024

See Food and an Oriole Doubleheader

The rain and clouds have at last departed. With blue skies and sunshine to remind us just how wonderful a spring afternoon can be, we took a stroll at Memorial Lake State Park in Lebanon County, Pennsylvania, to look for some migratory birds.

Though running just a few days later than usual, Indigo Buntings have arrived to begin nesting.

Shoreline Vegetation at Memorial Lake — **Clear Water-** Memorial Lake is one of the few man-made lakes in the Lower Susquehanna River Watershed to be appropriately vegetated with an abundance of submerged, floating, and emergent plants. As a result, the water from Indiantown Run that passes through the impoundment is minimally impacted by nutrient loads and the algal blooms they can cause. Buffers of woody and herbaceous growth along the lake’s shorelines provide additional nutrient sequestering and help prevent soil erosion and siltation.

The breeding season has begun for Neotropical migrants including this Baltimore Oriole, which we found defending a nesting territory in a stand of Black Walnut trees.

Along the edge of the lake, this Orchard Oriole and its mate were in yet another stand of tall walnut trees.

Early in the season and early in the day, we started seeing Common Nighthawks flying above wooded areas north of the lake at 4 o’clock this afternoon. After all the raw and inclement weather they’ve experienced in recent days, the warm afternoon was probably their first opportunity to feed on flying insects in quite a while.

What? You thought we were gonna drop in on Maryland’s largest city for a couple of ball games and some oysters, clams, and crab cakes—not likely.

March 28, 2024March 28, 2024

Chesapeake Bay Maritime Accidents and Their Impact on Susquehanna Wildlife

Tuesday’s collision of the container ship Dali into Baltimore’s Francis Scott Key Bridge and the nearly immediate collapse of the span into the chilly waters below reminds us just how unforgiving and deadly maritime accidents can be. Upon termination of rescue and recovery operations, salvage and cleanup will be prioritized as the next steps in the long-term process of reopening the navigable waters to ship traffic and construction of a new bridge. Part of the effort will include monitoring for leaks of fuels and other hazardous materials from the ship, its damaged cargo containers, and vehicles and equipment that were on the bridge when it failed.

Dali vs. Francis Scott Key Bridge — Damage to the hull of the Dali and to the cargo containers on her deck could lead to leaks of hazardous liquids or other materials into Chesapeake Bay. (United States Army Corps of Engineers Baltimore image)

On the waters and shores of today’s Chesapeake, numerous county, state, and federal agencies, including the United States Coast Guard, monitor and inspect looking for conditions and situations that could lead to point-source or accidental discharges of petroleum products and other hazardous materials into the bay. Many are trained, equipped, and organized for emergency response to contain and mitigate spills upon detection. But this was not always the case.

Through much of the twentieth century, maritime spills of oil and other chemicals magnified the effects of routine discharges of hazardous materials and sanitary sewer effluent into the Chesapeake and its tributaries. The cumulative effect of these pollutants progressively impaired fisheries and bay ecosystems leading to noticeable declines in numbers of many aquatic species. Rather frequently, spills or discharges resulted in conspicuous fish and/or bird kills.

One of the worst spills occurred near the mouth of the Potomac River on February 2, 1976, when a barge carrying 250,000 gallons of number 6 oil sank in a storm and lost its cargo into the bay. During a month-long cleanup, the United States Coast Guard recovered approximately 167,000 gallons of the spilled oil, the remainder dispersed into the environment. A survey counted 8,469 “sea ducks” killed. Of the total number, the great majority were Horned Grebes (4,347 or 51.3%) and Long-tailed Ducks (2,959 or 34.9%). Other species included Surf Scoter (Melanitta perspicillata) (405 or 4.8%), Common Loon (195 or 2.3%), Bufflehead (166 or 2.0%), Ruddy Duck (107 or 1.3%), Common Goldeneye (78 or 0.9%), Tundra Swan (46 or 0.5%), Greater Scaup (19 or 0.2%), American Black Duck (12 or 0.2%), Common Merganser (11 or 0.1%), Canvasback (10 or 0.1%), Double-crested Cormorant (10 or 0.1%), Canada Goose (8 or 0.1%), White-winged Scoter (Melanitta deglandi) (7 or 0.1%), Redhead (5 or 0.1%), gull species (10 or 0.1%), miscellaneous ducks and herons (13 or 0.2%) and unidentified (61 or 0.7%). During the spring migration, a majority of these birds would have made their way north and passed through the lower Susquehanna valley. The accident certainly impacted the occurrence of the listed species during that spring in 1976, and possibly for a number of years after.

Horned Grebe during migration on the Susquehanna near Haldeman Riffles. — Of the 8,469 birds killed by the February 2, 1976, oil spill on the Chesapeake, 51.3% (4,347) were Horned Grebes. Many of them would have migrated north through the Lower Susquehanna River Watershed during the coming spring.

The Federal Water Pollution Control Act Amendments of 1972, commonly known as the Clean Water Act, put teeth into the original FWCPCA of 1948 and began reversing the accumulation of pollutants in the bay and other bodies of water around the nation. Additional amendments in 1977 and 1987 have strengthened protections and changed the culture of “dump-and-run” disposal and “dilution-is-the-solution” treatment of hazardous wastes. During the late nineteen-seventies and early nineteen-eighties, emergency response teams and agencies began organizing to control and mitigate spill events. The result has been a greater awareness and competency for handling accidental discharges of fuels and other chemicals into Chesapeake Bay and other waterways. These improvements can help minimize the environmental impact of the Dali’s collision with the Francis Scott Key Bridge in Baltimore.

Oil spills and other pollution in the Chesapeake can impact populations of migratory fish including the anadromous Hickory Shad which are presently transiting the bay on their way to the waters of the Susquehanna below Conowingo Dam.

SOURCES

Roland, John V., Moore, Glenn E., and Bellanca, Michael A. 1977. “The Chesapeake Bay Oil Spill—February 2, 1976: A Case History”. International Oil Spill Conference Proceedings (1977). 1977 (1): 523-527.

November 4, 2020November 3, 2024

Migrating Golden Eagles

Why would otherwise sensible people perch themselves atop a rocky outcrop on a Pennsylvania mountaintop for ten hours on a windy bone-numbing bitter cold and sometimes snowy November day? To watch migrating raptors of course.

November is the time when big hawks and eagles migrate through and into the lower Susquehanna valley. And big birds rely on big wind to create updrafts and an easy ride along the region’s many ridges. The most observable flights often accompany the arrival of cold air surging across the Appalachian Mountains from the northwest. These conditions can propel season-high numbers of several of the largest species of raptors past hawk-counting sites.

Observers brave howling winds on the Waggoner’s Gap lookout to census migrating late-season raptors.

Earlier this week, two windy days followed the passage of a cold front to usher-in spectacular hawk and eagle flights at the the Waggoner’s Gap Hawk Watch station on Blue Mountain north of Carlisle, Pennsylvania. Steady 30 M.P.H. winds from the northwest on Monday, November 2, gusted to 50 M.P.H. at times. Early that morning, two Rough-legged Hawks, rarities at eastern hawk watches, were seen. They and two American Goshawks (Astur atricapillus) provided a preview of the memorable sightings to come. Two dozen Golden Eagles migrated past the lookout that day. Then on November 3, thirty Golden Eagles were tallied, despite west winds at speeds not exceeding half those of the day before.

Here are some of the late-season raptors seen by hardy observers at Waggoner’s Gap on Monday and Tuesday, November 2 & 3.

In November, Red-tailed Hawks are the most common migratory raptor counted at hawk watch stations in the Susquehanna region.

A juvenile American Goshawk passes the Waggoner's Gap lookout. — An uncommon bird, a juvenile American Goshawk, passes the Waggoner’s Gap lookout.

An adult Golden Eagle circles on an updraft along the north face of Blue Mountain to gain altitude before continuing on its journey.

The plumage of juvenile and immature Golden Eagles often creates a sensation among crowds at a lookout. Golden Eagles don’t attain a full set of adult feathers until their sixth year. This individual is probably a juvenile, also known as a hatch-year or first-year bird. At most, it could be in its second year. Click the “Golden Eagle Aging Chart” tab on this page to learn more about these uncommon migrants and their molt sequences as they mature.

The gilded head feathers of a Golden Eagle glisten in the afternoon sun.

An adult Golden Eagle passing Waggoner’s Gap. The population known as “Eastern Golden Eagles” winters in the Appalachian Mountains and, with increasing frequency, on the Piedmont and Atlantic Coastal Plain Provinces of the eastern United States, where it often subsists as a scavenger.

Another first-year (juvenile) or second-year Golden Eagle.

A local Red-tailed Hawk (top left) trying to bully a migrating Golden Eagle. A dangerous business indeed.

Through December, Bald Eagles, presently the more common of our eagle species, are regular migrants at Waggoner’s Gap and other Susquehanna valley hawk watch sites.

Red-shouldered Hawks are reliable early November migrants.

An adult Red-shouldered Hawk from above.

And an adult Red-shouldered Hawk from below.

Though their numbers peak in early October, Sharp-shinned Hawks, particularly adults like this one, continue to be seen through early November.

A Northern Harrier on the glide path overhead.

Merlins, like other falcons, are more apt to be seen in late September and October, but a few trickle through in November.

While visiting a hawk watch, one will certainly have the opportunity to see other birds too.

Common Ravens are fascinating birds and regular visitors to the airspace around hawk watches. Most are residents, but there appears to be some seasonal movement, particularly among younger birds.

Most people think of Common Loons as birds of northern lakes. But loons spend their winters in the ocean surf, and to get there they fly in loose flocks over the Lower Susquehanna River Watershed each spring and fall. They are regularly seen by observers at hawk watches.

Like ducks, geese, and swans, migrating Double-crested Cormorants assemble into aerodynamic V-shaped flocks to conserve energy.

Pine Siskins continue their invasion from the north. Dozens of small flocks numbering 10 to 20 birds each continue to be seen and/or heard daily at Waggoner’s Gap. A flock of Evening Grosbeaks (Coccothraustes vesperitinus), another irruptive species of “winter finch”, was seen there on November 3.

As a finale of sorts, near the close of the day on November 3, two Golden Eagles sailed past the north side of the Waggoner’s Gap lookout, one possessing what appeared to be a tracking transmitter on its back. An effort was commenced by the official count staff to report the sighting to the entity monitoring the bird—to track down the tracker, so to speak.

A Golden Eagle with a backpack transmitter passing Waggoner’s Gap Hawk Watch at 3:39 P.M. Eastern Standard Time on November 3, 2020.

To see the count reports from Waggoner’s Gap and other hawk watches throughout North America, be certain to visit hawkcount.org

April 5, 2020April 6, 2020

Get Away From It All

For those of you who dare to shed that filthy contaminated rag you’ve been told to breathe through so that you might instead get out and enjoy some clean air in a cherished place of solitude, here’s what’s around—go have a look.

Northern Flickers have arrived. Look for them anywhere there are mature trees. Despite the fact that flickers are woodpeckers, they often feed on the ground. You’ll notice the white rump and yellow wing linings when they fly away.

The tiny Chipping Sparrow frequently nests in small trees in suburban gardens. Lay off the lawn treatments to assure their success.

Field Sparrows (Spizella fusilla) are a breeding species in abandoned fields where successional growth is underway.

White-throated Sparrows spend the winter in the lower Susquehanna valley. Their numbers are increasing now as waves of migrants pass through on their way north.

Northbound flocks of Rusty Blackbirds (Euphagus carolinus) are currently found feeding in forest swamps along the Susquehanna. Their noisy calls sound like a chorus of squeaking hinges.

Migratory Red-shouldered Hawks are also making feeding stops at area wetlands.

The Palm Warbler (Setophaga palmarum) is easily identified by its tail pumping behavior. Look for it in shrubs along the river shoreline or near lakes and streams. Palm Warblers are among the earliest of the warblers to move through in the spring.

The springtime show on the water continues…

Common Loons will continue migrating through the area during the upcoming month.

Buffleheads are still transiting the watershed.

Horned Grebes are occurring on the river and on local lakes.

Seeing these one-year-old male Hooded Mergansers, the bachelors, wandering around without any adult males or females is a good sign. The adults should have moved on to the breeding grounds and local pairs should be well into a nesting cycle by now. Hatching could occur any day.

Like Hooded Mergansers, Wood Ducks are cavity nesters, but their egg laying, incubation, and hatching often occurs a month or more later than that of the hoodies. Judging by the attentiveness of the drake, this pair of woodies is probably in the egg-laying stage of its breeding cycle right now.

Redheads (Aythya americana) are stopping for a rest on their way north.

In spring, Double-crested Cormorants proceed up the river in goose-like flocks with adult birds like these leading the way.

Hey, what are those showy flowers?

That’s Lesser Celandine (Ficaria verna). It’s often called Fig Buttercup. In early April it blankets stream banks throughout the lower Susquehanna region. If you don’t remember seeing it growing like that when you were younger, there’s a reason. Lesser Celandine is an escape from cultivation that has become invasive. While the appearance is tolerable; it’s the palatability that ruins everything. It’s poisonous if eaten by people or livestock.

The Eastern Spring Beauty (Claytonia virginica) is a dainty native wildflower of riparian forests and other woodlands throughout the lower Susquehanna valley.

The Trout Lily (Erythronium americanum) is beginning to bloom now. It’s a native of the region’s damp forests.

Virginia Bluebells (Mertensia virginica) is not native to the Susquehanna watershed, but neither is it considered invasive. It creates colorful patches in riparian forests.

Dutchman’s Breeches (Dicentra cucullaria) is a strikingly beautiful native wildflower that grows on undisturbed forested slopes throughout the Susquehanna valley.

Wasn’t that refreshing? Now go take a walk.

March 29, 2020March 30, 2020

The Fallout Continues

Fog and mist lingered throughout the day, as did the migratory water birds on the river and lakes in the lower Susquehanna valley. As a continuation of yesterday’s post on the fallout, here’s a photo tour of some of the sites where ducks, loons, grebes, and other birds have gathered.

American Robins may have comprised a large portion of the northbound flight appearing on last evening’s radar images. Today, hundreds could be seen on soggy lawns where earthworms might be found near the surface. This flock was finding sustenance at Highspire’s Reservoir Park in Dauphin County.

This drake Gadwall (Mareca strepera) and two hens had dropped in for a visit at the Highspire Reservoir Park.

Hundreds of Buffleheads were on the fogged-in Susquehanna River at Harrisburg this afternoon. From Front Street and Maclay Street in front of the Pennsylvania Governor’s Mansion, they seemed to be everywhere in sight on the rain-swollen current. After passing downstream, flocks flew in a straight line formation just above the water’s surface as they made a short trip back up the river to then drift down through the channels once again.

A portion of a raft consisting of about three dozen Red-breasted Mergansers floats by the Pennsylvania Governor’s Mansion. Several of the hundred or more Scaup on the river intermingled with these mergansers from time to time.

A lone Long-tailed Duck (Clanqula hyemalis) near the aforementioned raft of mergansers. The Long-tailed Duck was formerly known as the Oldsquaw in North America. The common name used in Britain and Europe is now preferred.

Two of at least a hundred Horned Grebes (Podiceps auritus) seen in the Susquehanna at Harrisburg this afternoon.

American Coots (Fulica americana) at Memorial Lake State Park in Lebanon County.

One more Common Loon than yesterday at Memorial Lake.

A mixed raft of diving ducks and grebes at Memorial Lake.

A closeup of the same raft reveals Buffleheads, Scaup, Ring-necked Ducks, Ruddy Ducks (Oxyura jamaicensis), a Pied-billed Grebe, and Horned Grebes.

Stormy weather certainly is a birder’s delight.

March 28, 2020March 30, 2020

Fallout in the Lower Susquehanna River Watershed

Local birders enjoy going to the Atlantic coast of New Jersey and Delmarva in the winter. The towns and beaches host far fewer people than birds, and many of the species seen are unlikely to be found anywhere else in the region. Unusual rarities add to the excitement.

The regular seaside attraction in winter is the variety of diving ducks and similar water birds that feed in the ocean surf and in the saltwater bays. Most of these birds breed in Canada and many stealthily cross over the landmass of the northeastern United States during their migrations. If an inland birder wants to see these coastal specialties, a trip to the shore in winter or a much longer journey to Canada in the summer is normally necessary—unless there is a fallout.

Migrating birds can show up in strange places when a storm interrupts their flight. Forest songbirds like thrushes and warblers frequently take temporary refuge in a wooded backyard or even in a city park when forced down by inclement weather. Loons have been found in shopping center parking lots after mistaking the wet asphalt for a lake. Fortunately though, loons, ducks, and other water birds usually find suitable ponds, lakes, and rivers as places of refuge when forced down. For inland birders, a fallout like this can provide an opportunity to observe these coastal species close to home.

Not so coincidentally, it has rained throughout much of today in the Lower Susquehanna River Watershed, apparently interrupting a large movement of migrating birds. There is, at the time of this writing, a significant fallout of coastal water birds here. Hundreds of diving ducks and other benthic feeders are on the Susquehanna River and on some of the clearer lakes and ponds in the region. They can be expected to remain until the storm passes and visibility improves—then they’ll promptly commence their exodus.

The following photographs were taken during today’s late afternoon thundershower at Memorial Lake State Park at Fort Indiantown Gap, Lebanon County.

A one-year-old male Hooded Merganser (Lophodytes cucullatus).

Red-breasted Mergansers (Mergus serrator) are a familiar sight in saltwater bays, not so familiar on inland bodies of water.

A Common Loon that lands in a parking lot is unable to take flight again. It must be transported to a body of water large enough for it to run across the surface and get the speed it needs to take off and resume its flight. This Common Loon at Memorial Lake has selected an ideal fallout haven. It will have plenty of runway space when it decides to leave.

A Pied-billed Grebe (Podilymbus podiceps) in a heavy downpour.

Migrating land birds have also been forced down by the persistent rains.

The tail-pumping Eastern Phoebe is a common sight around the lower Susquehanna valley right now. Many will stay to breed, often building their nests under a man-made bridge, porch. or other structure.

Why not get out and take a slow quiet walk on a rainy day. It may be the best time of all for viewing certain birds and other wildlife.

Wild Turkeys (Meleagris gallopovo) will often leave the cover of woodlands and forest to forage in the open during a rain shower.

During the final hours of this evening, wind-assisted flights of northbound migrating birds are indicated as blue masses around radar sites south of the Mason-Dixon Line. These nocturnal flights may constitute yet another fallout in the area of the showers and storms shown passing west to east through Pennsylvania, adding to the existing concentration of grounded migrants in the lower Susquehanna valley. (NOAA/National Weather Service image)

November 4, 2017September 4, 2019

Feathered Fallout

The NOAA National Weather Service radar images from last evening provided an indication that there may be a good fallout of birds at daybreak in the lower Susquehanna valley. The moon was bright, nearly full, and there was a gentle breeze from the north to move the nocturnal migrants along. The conditions were ideal.

Rising from daytime roosts in New York and Pennsylvania, then streaming south in moonlit skies, migrating birds are recorded as echoes on this post-sunset composite NEXRAD loop from last evening. (NOAA/National Weather Service image)

The Riparian Woodlands at Conewago Falls were alive with migrants this morning. American Robins and White-throated Sparrows were joined by new arrivals for the season: Brown Creeper (Certhia americana), Ruby-crowned Kinglets (Regulus calendula), Golden-crowned Kinglets (Regulus satrapa), Dark-eyed Junco (Junco hyemalis), and Yellow-rumped Warbler (Setophaga coronata). These are the perching birds one would expect to have comprised the overnight flight. While the individuals that will remain may not yet be among them, these are the species we will see wintering in the Mid-Atlantic states. No trip to the tropics for these hardy passerines.

American Robins continued migratory flight into the first hour of daylight this morning. Their calls are commonly heard at night as migrating individuals pass overhead.

White-throated Sparrows are nocturnal migrants, and are a familiar find on woodland edges and at suburban feeding stations through the winter.

Dark-eyed Juncos, also nocturnal migrants, are common winter residents in the Lower Susquehanna River Watershed, frequently visiting bird feeders.

Heavy rain earlier this week in the Susquehanna River drainage basin has flooded most of the Pothole Rocks; the rapids of Conewago Falls have returned.

CLICK ON THE LOGO FOR TODAY’S MIGRATION COUNT TOTALS

October 28, 2017November 22, 2024

A Quick Getaway

It was a placid morning on Conewago Falls with blue skies dotted every now and then by a small flock of migrating robins or blackbirds. The jumbled notes of a singing Winter Wren (Troglodytes hiemalis) in the Riparian Woodland softly mixed with the sounds of water spilling over the dam. The season’s first Wood Ducks (Aix sponsa), Blue-winged Teal (Spatula discors), American Herring Gull (Larus smithsonianus), Horned Larks (Eremophila alpestris), and White-throated Sparrows (Zonotrichia albicollis) were seen.

There was a small ruckus when one of the adult Bald Eagles from a local pair spotted an Osprey passing through carrying a fish. This eagle’s effort to steal the Osprey’s catch was soon interrupted when an adult eagle from a second pair that has been lingering in the area joined the pursuit. Two eagles are certainly better than one when it’s time to hustle a skinny little Osprey, don’t you think?

But you see, this just won’t do. It’s a breach of eagle etiquette, don’t you know? Soon both pairs of adult eagles were engaged in a noisy dogfight. It was fussing and cackling and the four eagles going in every direction overhead. Things calmed down after about five minutes, then a staring match commenced on the crest of the dam with the two pairs of eagles, the “home team” and the “visiting team”, perched about 100 feet from each other. Soon the pair which seems to be visiting gave up and moved out of the falls for the remainder of the day. The Osprey, in the meantime, was able to slip away.

In recent weeks, the “home team” pair of Bald Eagles, seen regularly defending territory at Conewago Falls, has been hanging sticks and branched tree limbs on the cross members of the power line tower where they often perch. They seem only to collect and display these would-be nest materials when the “visiting team” pair is perched in the nearby tower just several hundred yards away…an attempt to intimidate by homesteading. It appears that with winter and breeding time approaching, territorial behavior is on the increase.

The second migrating Osprey of the day ran the gauntlet of marauding eagles without incident.

In the afternoon, a fresh breeze from the south sent ripples across the waters among the Pothole Rocks. The updraft on the south face of the diabase ridge on the east shore was like a highway for some migrating hawks, falcons, and vultures. Black Vultures (Coragyps atratus) and Turkey Vultures streamed off to the south headlong into the wind after leaving the ridge and crossing the river. A male and female Northern Harrier (Circus hudsonius), ten Red-tailed Hawks, two Red-shouldered Hawks (Buteo lineatus), six Sharp-shinned Hawks, and two Merlins crossed the river and continued along the diabase ridge on the west shore, accessing a strong updraft along its slope to propel their journey further to the southwest. Four high-flying Bald Eagles migrated through, each following the east river shore downstream and making little use of the ridge except to gain a little altitude while passing by.

(Top and Middle) Turkey Vultures riding the fresh breeze and teetering to-and-fro on up-tilted wings. This wing posture is known as a dihedral. (Bottom) More than 100 migrating Black Vultures climbed high on the afternoon breeze to make an oblique crossing of the river and maintain a southbound course.

Late in the afternoon, the local Bald Eagles were again airborne and cackling up a storm. This time they intercepted an eagle coming down the ridge toward the river and immediately forced the bird to climb if it intended to pass. It turned out to be the best sighting of the day, and these “home team” eagles found it first. It was a Golden Eagle (Aquila chrysaetos) in crisp juvenile plumage. On its first southward voyage, it seemed to linger after climbing high enough for the Bald Eagles to loose concern, then finally selected the ridge route and crossed the river to head off to the southwest.

Ring-billed Gulls began feeding during the afternoon as clouds preceding stormy weather approached.

October 14, 2017September 4, 2019

State of Confusion

The humid rainy remains of Hurricane Nate have long since passed by Pennsylvania, yet mild wet weather lingers to confuse one’s sense of the seasons. This gloomy misty day was less than spectacular for watching migrating birds and insects, but some did pass by. Many resident animals of the falls are availing themselves of the opportunity to continue active behavior before the cold winds of autumn and winter force a change of lifestyle.

Warm drizzle at daybreak prompted several Northern Spring Peepers (Pseudacris crucifer crucifer) to begin calling from the wetlands in the Riparian Woodlands of Conewago Falls. An enormous chorus of these calls normally begins with the first warm rains of early spring to usher in this tiny frog’s mating season. Today, it was just a few “peeps” among anxious friends.

The tiny Northern Spring Peeper is recognized by the dark “X” across its back. Soon, shelter must be found among loose bark and fallen logs to commence hibernation. Emergence, often prompted by warm spring rains, will quickly be followed by a growing chorus of breeding calls as sometimes hundreds of these frogs assemble in vernal pools where mating will then occur.

Any additional river flow that resulted from the rains of the previous week is scarcely noticeable among the Pothole Rocks. The water level remains low, the water column is fairly clear, and the water temperatures are in the 60s Fahrenheit.

It’s no real surprise then to see aquatic turtles climbing onto the boulders in the falls to enjoy a little warmth, if not from the sun, then from the stored heat in the rocks. As usual, they’re quick to slide into the depths soon after sensing someone approaching or moving nearby. Seldom found anywhere but on the river, these skilled divers are Common Map Turtles (Graptemys geographica), also known as Northern Map Turtles. Their paddle-like feet are well adapted to swimming in strong current. They are benthic feeders, feasting upon a wide variety of invertebrates found among the stone and substrate of the river bottom.

Adult Common Map Turtles hibernate communally on the river bottom in a location protected from ice scour and turbulent flow, often using boulders, logs, or other structures as shelter from strong current. The oxygenation of waters tumbling through Conewago Falls may be critical to the survival of the turtles overwintering downstream. Dissolved oxygen in the water is absorbed by the nearly inactive turtles as they remain submerged at their hideout through the winter. Though Common Map Turtles, particularly males, may occasionally move about in their hibernation location, they are not seen coming to the surface to breathe.

The Common Map Turtles in the Susquehanna River basin are a population disconnected from that found in the main range of the species in the Great Lakes and upper Mississippi basin. Another isolated population exists in the Delaware River.

Common Map Turtles, including this recently hatched young seen in August, are often observed climbing onto rocks in the river.

Note the oversize swimming fin adaptations of the feet on this adult Common Map Turtle found among the Pothole Rocks in Conewago Falls. Young and adults are capable of navigating some strong current to feed and escape danger.

SOURCES

Committee on the Status of Endangered Wildlife in Canada. 2002. Status Report of the Northern Map Turtle. Canadian Wildlife Service. Ottawa, Ontario.

September 30, 2017September 4, 2018

Swallows by the Thousands

A fresh breeze from the north brought cooler air and a reminder that summer is gone and autumn has arrived.

Fast-moving dark clouds provided a perfect backdrop for viewing passing diurnal migrants. Bald Eagles utilized the tail wind to cruise down the Susquehanna toward Chesapeake Bay and points further south. A migrating Merlin began a chase from which a Northern Flicker narrowly escaped by finding shelter among Pothole Rocks and a few small trees. The season’s first American Black Duck (Anas rubripes), Common Loon (Gavia immer), Yellow-bellied Sapsucker (Sphyrapicus varia), and American Pipits (Anthus rubescens) moved through.

Blue Jays continued their hesitant crossings of the river at Conewago Falls. The majority completed the journey by forming groups of a dozen or more birds and following the lead of a lone American Robin, a Northern Flicker, or, odd as it appeared, a small warbler.

By far the most numerous migrants today were swallows. Thousands of Northern Rough-winged Swallows and hundreds of Tree Swallows were on the wing in search of what was suddenly a sparse flying insect supply. To get out of the brisk wind, some of the more resourceful birds landed on the warm rocks. To satisfy their appetite, many were able to pick crawling arthropods from the surface of the boulders. They swallow them whole.