A Flock of Seagulls?

At the moment there is a heavy snow falling, not an unusual occurrence for mid-February, nevertheless, it is a change in weather.  Forty-eight hours ago we were in the midst of a steady rain and temperatures were in the sixties.  The snow and ice had melted away and a touch of spring was in the air.

Big Bluestem in the Riverine Grasslands is inundated by the rising waters of the Susquehanna at Conewago Falls.   The river ice has been dispersed by the recent mild temperatures and rains.

Anyone casually looking about while outdoors during these last several days may have noticed that birds are indeed beginning to migrate north in the lower Susquehanna valley.  Killdeer, American Robins, Eastern Bluebirds, Red-winged Blackbirds, and Common Grackles are easily seen or heard in most of the area now.

Just hours ago, between nine o’clock this morning and one o’clock this afternoon, there was a spectacular flight of birds following the river north, their spring migration well underway.  In the blue skies above Conewago Falls, a steady parade of Ring-billed Gulls was utilizing thermals and riding a tailwind from the south-southeast to cruise high overhead on a course toward their breeding range.

Ring-billed Gulls swarm in a thermal updraft above Conewago Falls to gain altitude prior to streaming off to the north and continuing their journey.
Ring-billed Gulls climbing to heights sometimes exceeding 1,000 feet before breaking off and gliding away to the north.

The swirling hoards of Ring-billed Gulls attracted other migrants to take advantage of the thermals and glide paths on the breeze.  Right among them were 44 Herring Gulls, 3 Great Black-backed Gulls, 12 Tundra Swans (Cygnus columbianus), 10 Canada Geese, 3 Northern Pintails (Anas acuta), 6 Common Mergansers, 3 Red-tailed Hawks, a Red-shouldered Hawk, 6 Bald Eagles (non-adults), 8 Black Vultures, and 5 Turkey Vultures.

A first-year Herring Gull (top center) is a standout in a “kettle” of Ring-billed Gulls.
How many Ring-billed Gulls passed by today?  More than 18,000…with emphasis on MORE THAN.  You see, early this afternoon, the handy-dandy clicker-counter used to tick off and tally the big flights of birds as they pass by quit clicking and counting.  Therefore, 18,000 is the absolute minimum number of Ring-billed Gulls seen migrating north today.  Hopefully the trusty old oil can will get the clicker working again soon.

In the afternoon, the clouds closed in quickly, the flight ended, and by dusk more than an inch of snow was on the ground.  Looks like spring to me.

Essential Ice

Two days ago, widespread rain fell intermittently through the day and steadily into the night in the Susquehanna drainage basin.  The temperature was sixty degrees, climbing out of a three-week-long spell of sub-freezing cold in a dramatic way.  Above the ice-covered river, a very localized fog swirled in the southerly breezes.

By yesterday, the rain had ended as light snow and a stiff wind from the northwest brought sub-freezing air back to the region.  Though less than an inch of rain fell during this event, much of it drained to waterways from frozen or saturated ground.  Streams throughout the watershed are being pushed clear of ice as minor flooding lifts and breaks the solid sheets into floating chunks.

Today, as their high flows recede, the smaller creeks and runs are beginning to freeze once again.  On larger streams, ice is still exiting with the cresting flows and entering the rising river.

Ice chunks on Swatara Creek merge into a dense flow of ice on the river in the distance.  Swatara Creek is the largest tributary to enter the Susquehanna in the Gettysburg Basin.  The risk of an ice jam impounding the Swatara here at its mouth is lessened because rising water on the river has lifted and broken the ice pack to keep it moving without serious impingement by submerged obstacles.  Immovable ice jams on the river can easily block the outflow from tributaries, resulting in catastrophic flooding along these streams.
Fast-moving flows of jagged ice race toward Three Mile Island and Conewago Falls.  The rising water began relieving the compression of ice along the shoreline during the mid-morning.  Here on the river just downstream of the mouth of Swatara Creek, ice-free openings allowed near-shore piles to separate and begin floating away after 10:30 A.M. E.S.T.  Moving masses of ice created loud rumbles, sounding like a distant thunderstorm.
Ice being pushed and heaved over the crest of the York Haven Dam at Conewago Falls due to compression and rising water levels.
Enormous chunks of ice being forced up and over the York Haven Dam into Conewago Falls and the Pothole Rocks below.
Ice scours Conewago Falls, as it has for thousands of years.
The action of ice and suspended abrasives has carved the York Haven Diabase boulders and bedrock of Conewago Falls into the amazing Pothole Rocks.
The roaring torrents of ice-choked water will clear some of the woody growth from the Riverine Grasslands of Conewago Falls.
To the right of center in this image, a motorcar-sized chunk of ice tumbles over the dam and crashes into the Pothole Rocks.  It was one of thousands of similar tree-and-shrub-clearing projectiles to go through the falls today.

The events of today provide a superb snapshot of how Conewago Falls, particularly the Diabase Pothole Rocks, became such a unique place, thousands of years in the making.  Ice and flood events of varying intensity, duration, and composition have sculpted these geomorphologic features and contributed to the creation of the specialized plant and animal communities we find there.  Their periodic occurrence is essential to maintaining the uncommon habitats in which these communities thrive.

Fish Crows (Corvus ossifragus) gather along the flooding river shoreline.  Soon there’ll be plenty of rubbish to pick through, some carrion maybe, or even a displaced aquatic creature or two to snack upon.

Eighteen, and I Like It

Is this the same Conewago Falls I visited a week ago?  Could it really be?  Where are all the gulls, the herons, the tiny critters swimming in the potholes, and the leaping fish?  Except for a Bald Eagle on a nearby perch, the falls seems inanimate.

Yes, a week of deep freeze has stifled the Susquehanna and much of Conewago Falls.  A hike up into the area where the falls churns with great turbulence provided a view of some open water.  And a flow of open water is found downstream of the York Haven Dam powerhouse discharge.  All else is icing over and freezing solid.  The flow of the river pinned beneath is already beginning to heave the flat sheets into piles of jagged ice which accumulate behind obstacles and shallows.

Ice and snow surround a small zone of open water in a high-gradient area of Conewago Falls.
Ice chunks and sheets accumulate atop the York Haven Dam.  The weight of miles of ice backed up behind the dam eventually forces the accumulation over the top and into the Pothole Rocks below.  The popping and cracking sounds of ice both above and below the dam could be heard throughout the day as hydraulic forces continuously break and move ice sheets.
Steam from the Unit 1 cooling towers at the Three Mile Island Nuclear Generating Station rises above the frozen Riverine Grasslands at Conewago Falls.  The scouring action of winter ice keeps the grasslands clear of substantial woody growth and prevents succession into forest.
Despite a lack of activity on the river, mixed flocks of resident and wintering birds, including this White-breasted Nuthatch (Sitta carolinensis), were busy feeding in the Riparian Woodlands.  The White-breasted Nuthatch is a cavity nester and year-round denizen of hardwoods, often finding shelter during harsh winter nights in small tree holes.
The White-breasted Nuthatch is often seen working its way head-first down a tree trunk as it probes with its well-adapted bill for insects among the bark.
Jackpot!
Looking upstream from the river’s east shore at ice and snow cover on the Susquehanna above Conewago Falls and the York Haven Dam.  The impoundment, known as Lake Frederic, and its numerous islands of the Gettysburg Basin Archipelago were locked in winter’s frosty grip today.  Hill Island (Left) and Poplar Island (Center) consist of erosion-resistant York Haven Diabase, as does the ridge on the far shoreline seen rising in the distance between them.  To the right of Poplar Island in this image, the river passes by the Harrisburg International Airport.  At the weather station there, the high temperature was eighteen degrees Fahrenheit on this first day of 2018.

Culinary Reminder

It was a crisp clear morning with birdless blue skies.  The migration has mostly drawn to a close; very little was seen despite a suitable northwest breeze to support a flight.   There were no robins and no blackbirds.  Not even a starling was seen today.  The only highlights were a Bufflehead (Bucephala albeola) and a couple of Swamp Sparrows.

A Swamp Sparrow is coaxed from the dense leafy cover of the Riverine Grasslands of Conewago Falls.
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And now ladies and gentlemen, boys and girls, it’s time for a Thanksgiving Day culinary reminder from the local Conewago Falls Turkey…

“That’s the Conewago Falls Turkey Vulture if you don’t mind.  And I’m here to remind you that this Thanksgiving, you don’t have to fight your way in there to get first pickings of the feast.  Take it from me, let those flavors and aromas intensify over time.  And juices, who needs juices?  Let that stuff congeal so everything sticks to your ribs.  Are you paying attention?  I’m telling you, just back off, let the crowd die down, then get in there and devour those leftovers.  They’re the best.  You’ll thank me later!”

Summertime Blues

Let’s imagine that you spend your summer as a singer and you have to strut your stuff in a blue suit all day long just so the other guys know that you’re not going to tolerate any nonsense with either of your two gals.  And…you’re responsible for feeding the adolescent kids while each of the girls begins a second family.  Wouldn’t you be ready for a break by late August?

The boys must think so.  They’re quiet now.  This week was the end.  They’ve done their duty.  They protected their homes and got the youngsters out on their own.  It’s time to eat, get out of the dress blues, and prepare to take a flight to warmer climates, maybe even the tropics…for a holiday of sorts.

The male Indigo Bunting (Passerina cyanea) has a busy schedule.  Before arriving at Conewago Falls in early May, he has molted from the plainest of plain brown plumage and donned an iridescent set of feathers that glow a brilliant blue and purple in sunlight.  He chooses a territory with plenty of shrubby and weedy growth along the edge of a woodland, and begins to sing and defend his parcel, often from a dead tree or other perch.

At Conewago Falls, the Indigo Bunting is a common breeding bird, finding the mosaic of electric transmission wire right-of-ways, railroads, and the Riverine Grasslands to be absolutely perfect habitat.  The female, inconspicuous in her uniformly brown plumage, builds the nest, incubates the 3 to 4 eggs (11 to 14 days), and feeds the young in the nest (9 to 12 days).  Being quite the showboats, some males will have more than one mate nesting in their territory.  In addition to defending the nest(s), the male Indigo Bunting will sometimes feed the fledged young so that the female(s) can begin incubating a second brood.  The summertime diet is mostly invertebrates, but seeds are also consumed.

A male Indigo Bunting defends nesting territory from a perch on a dead tree.

By late August, the young of the year are mostly on their own.  The male’s territorial urges, including the nearly non-stop singing, come to an end.  Soon, his blue feathers are beginning to drop and a molt is underway into a brown plumage resembling that of the females and juveniles.

Indigo Buntings evacuate their breeding range in eastern North America to winter mostly south of the United States.  These nocturnal travelers have been the subject of migration behavior studies.  They are among a number of small bird species known to cross the Gulf of Mexico on their way south.  Also, Indigo Buntings can navigate by the stars.

On the wintering grounds, Indigo Buntings are flocking birds.  At this time of year, they consume more seeds as a component of their diet and are known to visit bird feeders.

By April, the blue suit is back, and the males and females are on the way north.  Hope to see you then pal.

SOURCES

Dunne, Pete.  2006.  Pete Dunne’s Essential Field Guide Companion.  Houghton Mifflin Company.  New York.

Kaufman, Kenn.  1996.  Lives of North American Birds.  Houghton Mifflin Company.  New York.

Beauties

It’s tough being good-looking and liked by so many.  You’ve got to watch out, because popularity makes you a target.  Others get jealous and begin a crusade to have you neutralized and removed from the spotlight.  They’ll start digging to find your little weaknesses and flaws, then they’ll exploit them to destroy your reputation.  Next thing you know, people look at you as some kind of hideous scoundrel.

Today, bright afternoon sunshine and a profusion of blooming wildflowers coaxed butterflies into action.  It was one of those days when you don’t know where to look first.

A Pearl Crescent (Phyciodes tharos) sipping nectar from Rough Boneset (Eupatorium pilosum) flowers.  Asters (Aster) are the host plants for the larvae of this butterfly.
A Buckeye (Junonia coenia) on Rough Boneset.  Its caterpillars are known to feed on members of the Acanthus family, possibly including the Water Willow (Justicia americana) which is so abundant in Conewago Falls.
Visitors from south of the Mason-Dixon Line arrived on the recent warm winds.  Two Cloudless Sulphurs (Phoebis sennae) patrolled the Riverine Grasslands, especially near the stands of Partridge Pea, a possible host plant.  One is seen here visiting a Halbred-leaved Rose Mallow blossom.  These large yellow butterflies are always a standout.

Purple Loosestrife (Lythrum salicaria) has a bad reputation.  Not native to the Americas, this prolific seed producer began spreading aggressively into many wetlands following its introduction.  It crowds out native plant species and can have a detrimental impact on other aquatic life.  Stands of loosestrife in slow-moving waters can alter flows, trap sediment, and adversely modify the morphology of waterways.  Expensive removal and biological control are often needed to protect critical habitat.

The dastardly Purple Loosestrife may have only two positive attributes.  First, it’s a beautiful plant.  And second, it’s popular; butterflies and other pollinators find it to be irresistible and go wild over the nectar.

A Silver-spotted Skipper (Epargyreus clarus) feeding on Purple Loosestrife nectar.  The host plants for this common butterfly’s caterpillars are a wide variety of Legumes.
A Cabbage White (Pieris rapae), a butterfly introduced from Europe in the 1800s, feeds on introduced Purple Loosestrife.
A Wild Indigo Duskywing (Erynnis baptisiae) feeding on Purple Loosestrife. This butterfly has expanded its population and range by using the introduced Crown Vetch as a host plant.

Don’t you just adore the wonderful butterflies.  Everybody does.  Just don’t tell anyone that they’re pollinating those dirty filthy no-good Purple Loosestrife plants.

SOURCES

Brock, Jim P., and Kenn Kaufman.  2003.  Butterflies of North America.  Houghton Mifflin Company.  New York.

Newcomb, Lawrence.  1977.  Newcomb’s Wildflower Guide.  Little, Brown and Company.  Boston, Massachusetts.

The Dungeon

There’s something frightening going on down there.  In the sand, beneath the plants on the shoreline, there’s a pile of soil next to a hole it’s been digging.  Now, it’s dragging something toward the tunnel it made.  What does it have?  Is that alive?

We know how the system works, the food chain that is.  The small stuff is eaten by the progressively bigger things, and there are fewer of the latter than there are of the former, thus the whole network keeps operating long-term.  Some things chew plants, others devour animals whole or in part, and then there are those, like us, that do both.  In the natural ecosystem, predators keep the numerous little critters from getting out of control and decimating certain other plant or animal populations and wrecking the whole business.  When man brings an invasive and potentially destructive species to a new area, occasionally we’re fortunate enough to have a native species adapt and begin to keep the invader under control by eating it.  It maintains the balance.  It’s easy enough to understand.

Japanese Beetles (Popillia japonica) seen here on Halberd-leaved Rose Mallow.  Without predation, exploding numbers of this invasive non-indigenous insect can defoliate and kill numerous species of plants in a given area.
The Song Sparrow (Melospiza melodia) is a generalist feeder, eating seeds and invertebrates including Japanese Beetles.  This species is the omnipresent year-round occupant of shoreline vegetation along the lower Susquehanna River.

Late summer days are marked by a change in the sounds coming from the forests surrounding the falls.  For birds, breeding season is ending, so the males cease their chorus of songs and insects take over the musical duties.  The buzzing of the male “Annual Cicada” (Tibicen) is the most familiar.  The female cicada lays its eggs in the twigs of trees.  After hatching, the nymphs drop to the ground and burrow to live and feed along tree roots for the next two to five years.  A dry exoskeleton clinging to a tree trunk is evidence that a nymph has emerged from the soil and flown away as an adult.  There are adult Annual Cicadas present every year.

An “Annual Cicada”, probably a Silver-bellied Cicada (Tibicen pruinosa), clings to a stem on a Halberd-leaved Rose Mallow at Conewago Falls.

For the adult cicada, there is danger.  It looks like an enormous bee.  It’s a Cicada Killer (Specius speciosus) wasp, and it will latch onto a cicada and begin stinging while both are in flight.  The stings soon paralyze the screeching panicked cicada.  The Cicada Killer then begins the task of airlifting and/or dragging its victim to the lair it has prepared.  The cicada is placed in one of more than a dozen cells in the tunnel complex where it will serve as food for the wasp’s larvae.  The wasp lays an egg on the cicada, then leaves and pushes the hole closed.  The egg hatches in a several days and the larval grub is on its own to feast upon the hapless cicada.

A Cicada Killer (Sphecius speciosus) along the river shoreline. Despite their intimidating appearance, they do not sting humans and can be quite docile when approached.

Other species in the Solitary Wasp family (Sphecidae) have similar life cycles using specific prey which they incapacitate to serve as sustenance for their larvae.

A Solitary Wasp, probably of the genus Ammophila, drags a paralyzed moth caterpillar to its breeding dungeon in the sandy soil at Conewago Falls.  For the victim, there is no escape from the crypt.

The Solitary Wasps are an important control on the populations of their respective prey.  Additionally, the wasp’s bizarre life cycle ensures a greater survival rate for its own offspring by providing sufficient food for each of its progeny before the egg beginning its life is ever put in place.  It’s complete family planning.

The cicadas reproduce quickly and, as a species, seem to endure the assault by Cicada Killers, birds, and other predators.  The Periodical Cicadas (Magicicada), with adult flights occurring as a massive swarm of an entire population every thirteen or seventeen years, survive as species by providing predators with so ample a supply of food that most of the adults go unmolested to complete reproduction.  Stay tuned, 2021 is due to be the next Periodical Cicada year in the vicinity of Conewago Falls.

SOURCES

Eaton, Eric R., and Kenn Kaufman.  2007.  Kaufman Field Guide to Insects of North America.  Houghton Mifflin Company.  New York.

S’more

The tall seed-topped stems swaying in a summer breeze are a pleasant scene.  And the colorful autumn shades of blue, orange, purple, red, and, of course, green leaves on these clumping plants are nice.  But of the multitude of flowering plants, Big Bluestem, Freshwater Cordgrass, and Switchgrass aren’t much of a draw.  No self-respecting bloom addict is going out of their way to have a gander at any grass that hasn’t been subjugated and tamed by a hideous set of spinning steel blades.  Grass flowers…are you kidding?

Big Bluestem in flower in the Riverine Grasslands at Conewago Falls.

O.K., so you need something more.  Here’s more.

Meet the Partridge Pea (Chamaecrista fasciculata).  It’s an annual plant growing in the Riverine Grasslands at Conewago Falls as a companion to Big Bluestem.  It has a special niche growing in the sandy and, in summertime, dry soils left behind by earlier flooding and ice scour.  The divided leaves close upon contact and also at nightfall.  Bees and other pollinators are drawn to the abundance of butter-yellow blossoms.  Like the familiar pea of the vegetable garden, the flowers are followed by flat seed pods.

The Partridge Pea can tolerate dry sandy soils.

But wait, here’s more.

In addition to its abundance in Conewago Falls, the Halberd-leaved Rose Mallow (Hibiscus laevis) is the ubiquitous water’s edge plant along the free-flowing Susquehanna River for miles downstream.  It grows in large clumps, often defining the border between the emergent zone and shore-rooted plants.  It is particularly successful in accumulations of alluvium interspersed with heavier pebbles and stone into which the roots will anchor to endure flooding and scour.  Such substrate buildup around the falls, along mid-river islands, and along the shores of the low-lying Riparian Woodlands immediately below the falls are often quite hospitable to the species.

Halberd-leaved Rose Mallow is a durable inhabitant of the falls.  Regular flooding keeps competing species at bay.  A taproot helps to safeguard against dislocation, allowing plants to grow in places subjected to turbulent currents.
Halberd-leaved Rose Mallow in bloom.  The similarity to cultivated members of the Hibiscus genus can readily be seen.  It is one of the showiest of perennial wildflowers in the floodplain.  Note the lobed, halberd-shaped leaves, source of its former species name militaris.
The seeds of Halberd-leaved Rose Mallow are contained in bladders which can float to assist in their distribution.  Some of these bladders cling to the dead leafless stems in winter, making it an easy plant to identify in nearly any season.

A second native wildflower species in the genus Hibiscus is found in the Conewago Falls floodplain, this one in wetlands.  The Swamp Rose Mallow (H. moscheutos) is similar to Halberd-leaved Rose Mallow, but sports more variable and colorful blooms.  The leaves are toothed without the deep halberd-style lobes and, like the stems, are downy.  As the common name implies, it requires swampy habitat with ample water and sunlight.

Swamp Rose Mallow in a sunny wetland.  This variety with solid-colored flowers (without dark centers) and pale green leaves and stems was formerly known as a separate species of  Swamp Rose Mallow, H. palustris.  Note that the flowers are terminal on the stems.
A few scattered specimens of a more typical variety of Swamp Rose Mallow are found on the shoreline and in the Riverine Grasslands of Conewago Falls.  The blooms are bright pink with darker centers and the leaf stems are robust and reddish.  This one is seen growing among Halberd-leaved Rose Mallow, with which it shares the characteristic of having flower stems growing from some of the upper leaf axils.  A variety with red-centered white flowers is often found throughout the plant’s range.

In summary, we find Partridge Pea in the Riverine Grasslands growing in sandy deposits left by flood and ice scour.  We find Halberd-leaved Rose Mallow rooted at the border between shore and the emergent zone.  We find Swamp Rose Mallow as an emergent in the wetlands of the floodplain.  And finally, we find marshmallows in only one location in the area of Conewago Falls.  Bon ap’.

Here’s S’more

SOURCES

Newcomb, Lawrence.  1977.  Newcomb’s Wildflower Guide.  Little, Brown and Company.  Boston, Massachusetts.

Summer Grasses

It has not been a good summer if you happen to be a submerged plant species in the lower Susquehanna River.  Regularly occurring showers and thunderstorms have produced torrents of rain and higher than usual river stages.  The high water alone wouldn’t prevent you from growing, colonizing a wider area, and floating several small flowers on the surface, however, the turbidity, the suspended sediment, would.  The muddy current casts a dirty shadow on the benthic zone preventing bottom-rooted plants from getting much headway.  There will be smaller floating mats of the uppermost leaves of these species.  Fish and invertebrates which rely upon this habitat for food and shelter will find sparse accommodation…better luck next year.

Due to the dirty water, fish-eating birds are having a challenging season as they try to catch sufficient quantities of prey to feed themselves and their offspring.  A family of Ospreys (Pandion haliaetus) at Conewago Falls, including recently fledged young, were observed throughout this morning and had no successful catches.  Of the hundred or more individual piscivores of various species present, none were seen retrieving fish from the river.  The visibility in the water column needs to improve before fishing is a viable enterprise again.

Ospreys competing for a suitable fishing perch.  Improving water conditions in the coming week should increase their success as predators.
Versatile at finding food, adult Bald Eagles are experienced and know to be on the lookout for Ospreys with fish, a meal they can steal through intimidation.

While the submerged plant communities may be stunted by 2017’s extraordinary water levels, there is a very unique habitat in Conewago Falls which endures summer flooding and, in addition, requires the scouring effects of river ice to maintain its mosaic of unique plants.  It is known as a Riverine Grassland or scour grassland.

The predominant plants of the Riverine Grasslands are perennial warm-season grasses.  The deep root systems of these hardy species have evolved to survive events which prevent the grassland from reverting to woodland through succession.  Fire, intense grazing by wild herd animals, poor soils, drought, and other hardships, including flooding and ice scour, will eliminate intolerant plant species and prevent an area from reforesting.  In winter and early spring, scraping and grinding by flood-driven chunk ice mechanically removes large woody and poorly rooted herbaceous growth from susceptible portions of the falls.  These adverse conditions clear the way for populations of species more often associated with North America’s tall grass prairies to take root.  Let’s have a look at some of the common species found in the “Conewago Falls Pothole Rocks Prairie”.

Big Bluestem (Andropogon gerardi), seen here growing in the cracks of a pothole rock. High water nourishes the plant by filling the crevices with nutrient-loaded sediment. This species evolved with roots over three feet deep to survive fires, trampling by bison, and drought.
Freshwater Cordgrass (Spartina pectinata) does well with its roots in water.  It creates exceptional bird habitat and grows in the falls and on ice-scoured small islands in free-flowing segments of the Susquehanna River downstream.
Switchgrass (Panicum virgatum), like Big Bluestem, is one of the tall grass prairie species and, like Freshwater Cordgrass, grows in near pure stands on ice-scoured islands.  It takes flooding well and its extensive root system prevents erosion.
Though not a grass, Water Willow (Justicia americana) is familiar as a flood-enduring emergent plant of river islands, gravel bars, and shorelines where its creeping rhizome root system spreads the plant into large masses.  These stands are often known locally as “grass beds”.  This member of the acanthus family provides habitat for fish and invertebrates among its flooded leaves and stems.  Its presence is critical to aquatic life in a year such as this.

The Conewago Falls Riverine Grassland is home to numerous other very interesting plants.  We’ll look at more of them next time.

SOURCES

Brown, Lauren.  1979.  Grasses, An Identification Guide.  Houghton Mifflin Company.  New York, NY.

Fussy Eaters

She ate only toaster pastries…that’s it…nothing else.  Every now and then, on special occasions, when a big dinner was served, she’d have a small helping of mashed potatoes, no gravy, just plain, thank you.  She received all her nutrition from several meals a week of macaroni and cheese assembled from processed ingredients found in a cardboard box.  It contains eight essential vitamins and minerals, don’t you know?  You remember her, don’t you?

Adult female butterflies must lay their eggs where the hatched larvae will promptly find the precise food needed to fuel their growth.  These caterpillars are fussy eaters, with some able to feed upon only one particular species or genus of plant to grow through the five stages, the instars, of larval life.  The energy for their fifth molt into a pupa, known as a chrysalis, and metamorphosis into an adult butterfly requires mass consumption of the required plant matter.  Their life cycle causes most butterflies to be very habitat specific.  These splendid insects may visit the urban or suburban garden as adults to feed on nectar plants, however, successful reproduction relies upon environs which include suitable, thriving, pesticide-free host plants for the caterpillars.  Their survival depends upon more than the vegetation surrounding the typical lawn will provide.

The Monarch (Danaus plexippus), a butterfly familiar in North America for its conspicuous autumn migrations to forests in Mexico, uses the milkweeds (Asclepias) almost exclusively as a host plant.  Here at  Conewago Falls, wetlands with Swamp Milkweed (Asclepias incarnata) and unsprayed clearings with Common Milkweed (A. syriaca) are essential to the successful reproduction of the species.  Human disturbance, including liberal use of herbicides, and invasive plant species can diminish the biomass of the Monarch’s favored nourishment, thus reducing significantly the abundance of the migratory late-season generation.

Monarch caterpillar after a fourth molt.  The fifth instar feeding on Swamp Milkweed.
A fifth molt begets the Monarch pupa, the chrysalis, from which the showy adult butterfly will emerge.
Adult Monarch feeding on Goldenrod (Solidago) nectar.

Butterflies are good indicators of the ecological health of a given environment.  A diversity of butterfly species in a given area requires a wide array of mostly indigenous plants to provide food for reproduction.  Let’s have a look at some of the species seen around Conewago Falls this week…

An adult Silvery Checkerspot (Chlosyne nycteis) visiting a nectar plant, Partridge Pea (Chamaecrista fasciculata).  Wingstem (Verbesina alternifolia), a plant of the Riparian Woodlands, is among the probable hosts for the caterpillars.
A Gray Hairstreak (Strymon melinus) visits Crown Vetch, a possible host plant.  Other potential larval food in the area includes Partridge Pea, Halberd-leaved Rose Mallow (Hibiscus laevis) of the river shoreline, and Swamp Rose Mallow (Hibiscus moscheutos), a plant of wetlands.
The Eastern Tailed Blue (Cupido comyntas) may use Partridge Pea , a native wildflower species, and the introduced Crown Vetch (Securigera/Coronilla varia) as host and nectar plants at Conewago Falls.
The Least Skipper (Ancyloxypha numitor) is at home among tall grasses in woodland openings, at riverside, and in the scoured grassland habitat of the Pothole Rocks in the falls.  Host plants available include Switchgrass (Panicum vigatum), Freshwater Cordgrass (Spartina pectinata), and Foxtails (Setaria).
The Zabulon Skipper (Poanes zabulon) is an inhabitant of moist clearings where the caterpillars may feed upon Lovegrasses (Eragrostis) and Purpletop (Tridens flavus).
The Eastern Tiger Swallowtail (Papilio glaucus), a female seen here gathering nectar from Joe-Pye Weed (Eutrochium), relies upon several forest trees as hosts. Black Cherry (Prunus serotina), Willow (Salix), Yellow Poplar (Liriodendron tulipifera), also known as Tuliptree, and Green Ash (Fraxinus pennsylvanica) are among the local species known to be used.  The future of the latter food species at Conewago Falls is doubtful.  Fortunately for the Eastern Tiger Swallowtail, the “generalist” feeding requirements of this butterfly’s larvae enable the species to survive the loss of a host plant.
A female Eastern Tiger Swallowtail, black morph, gathering nectar from Joe-Pye Weed.
The Zebra Swallowtail (Protographium marcellus), seen here on Joe-Pye Weed, feeds exclusively upon Pawpaw (Asimina) trees as a caterpillar.  This butterfly species may wander, but its breeding range is limited to the moist Riparian Woodlands where colonial groves of Pawpaw may be found.  The Common Pawpaw (Asimina triloba), our native species in Pennsylvania, and the Zebra Swallowtail occur at the northern edge of their geographic ranges in the Lower Susquehanna River Watershed.  Planting Pawpaw trees as an element of streamside reforestation projects certainly benefits this marvelous butterfly.

The spectacularly colorful butterflies are a real treat on a hot summer day.  Their affinity for showy plants doubles the pleasure.

By the way, I’m certain by now you’ve recalled that fussy eater…and how beautiful she grew up to be.

SOURCES

Brock, Jim P., and Kaufman, Kenn.  2003.  Butterflies of North America.  Houghton Mifflin Company.  New York, NY.