Birds Along the River’s Edge

Just as bare ground along a plowed road attracts birds in an otherwise snow-covered landscape, a receding river or large stream can provide the same benefit to hungry avians looking for food following a winter storm.

Here is a small sample of some of the species seen during a brief stop along the Susquehanna earlier this week.

Song Sparrow
Along vegetated edges of the Susquehanna and its tributaries, the Song Sparrow is ubiquitous in its search for small seeds and other foods.  As the river recedes from the effects of this month’s rains, the shoreline is left bare of more recently deposited snow cover.  Song Sparrows and other birds are attracted to streamside corridors of frost-free ground to find sufficient consumables for supplying enough energy to survive the long cold nights of winter.
American Robin
Thousands of American Robins have been widespread throughout the lower Susquehanna valley during the past week.  Due to the mild weather during this late fall and early winter, some may still be in the process of working their way south.  Currently, many robins are concentrated along the river shoreline where receding water has exposed unfrozen soils to provide these birds with opportunities for finding earthworms (Lumbricidae) and other annelids.
Golden-crowned Kinglet
This Golden-crowned Kinglet was observed searching the trees and shrubs along the Susquehanna shoreline for tiny insects and spiders. Temperatures above the bare ground along the receding river can be a few degrees higher than in surrounding snow-covered areas, thus improving the chances of finding active prey among the trunks and limbs of the riparian forest.
Brown Creeper
Not far from the kinglet, a Brown Creeper is seen searching the bark of a Silver Maple (Acer saccharinum) for wintering insects, as well as their eggs and larvae.  Spiders in all their life stages are a favorite too.
American Pipits
American Pipits not only inhabit farm fields during the winter months, they are quite fond of bare ground along the Susquehanna.  Seen quite easily along a strip of pebbly shoreline exposed by receding water, these birds will often escape notice when spending time on mid-river gravel and sand bars during periods of low flow.
An American Pipit on a bitterly cold afternoon along the Susquehanna.
An American Pipit on a bitterly cold afternoon along the Susquehanna.

Photo of the Day

Spiders of the Lower Susquehanna River Watershed: "Tiger" Wolf Spider
A “Tiger” Wolf Spider (Tigrosa species) lurks beneath the doorstep at the susquehannawildlife.net headquarters.  These arachnids reach only about one inch in length but appear startlingly larger due to their husky build.  To feed, Wolf Spiders spin no web for snagging flying insects.  Instead, they keep watch with their eight eyes, then ambush or chase down suitable prey.  If handled roughly or pinched between an object such as a shoe and your skin, Wolf Spiders can inject a sore-producing venom.  We like having them around our entranceway, just to keep a few eyes on things.

Some Autumn Insects

With autumn coming to a close, let’s have a look at some of the fascinating insects (and a spider) that put on a show during some mild afternoons in the late months of 2019.

Bush Katydids (Scudderia species) are found in brushy habitats and along rural roadsides.  Their green summer color fades to brown, maroon, and gold to match the autumn foliage where they hide.  Bush katydids often remain active until a hard freeze finally does them in.
The Eastern Buck Moth (Hemileuca maia) is fuzzy, appearing to wear a warm coat for its autumn expeditions.  Adults emerge in October and may fly as late as December.  Females deposit their eggs on the twigs of Bear Oak (Quercus ilicifolia), Blackjack Oak (Q. marilandica), or Chestnut Oak (Q. montana), trees that, in our region, seem most favorable for the moth’s use when growing on burned barrens and mountain slopes.  The spiny caterpillars are known to feed only on the foliage of these few trees.  In the lower Susquehanna valley, the Eastern Buck Moth is rare because its specialized habitat is in short supply, and it’s all Smokey The Bear’s fault.
The Sachem (Atalopedes campestris) wanders north from the Atlantic Coastal Plain into the Susquehanna valley each summer.  In some years they become the most numerous small orange butterfly of all, particularly around home gardens.  The larvae will feed on Crabgrass (Digitaria species), but have not found success overwintering this far north.  By November, adults begin to look pretty drab.
From 1978 through 1982, the Asian Multicolored Lady Beetle (Harmonia axyridis) was introduced into the eastern states by the United States Department of Agriculture.  It has become a nuisance in many areas where it swarms, sometimes bites, and often overwinters in large smelly masses within homes and other warm buildings.  As you may have guessed, it’s possibly displacing some of the less aggressive native lady beetle species.
On a chilly afternoon, a sun-warmed Bold Jumping Spider (Phidippus audax) pounced and dispatched this sluggish worker Honey Bee (Apis mellifera) that was trying to gather pollen from a late-season Purple Coneflower bloom.  This spider is bold indeed.
Under bridges, inside bird nest boxes, and sometimes beneath porches, the female Pipe Organ Mud Dauber (Trypoxylon politum), a predatory wasp, builds these elaborate nests composed of long rows (pipes) of nursery cells.  Into each cell one or more paralyzed spiders is deposited along with one of the female’s eggs.  When hatched, each larva will feed upon the paralyzed spider(s) inside its cell, then pupate.  The pupae overwinter, then emerge from their cells as adults during the following spring.  In the autumn, males often stand guard at an entrance to the nest to prevent parasitic species, including some flies (look at the fifth pipe from the right), from laying eggs on the pupae.  These wasps are not aggressive toward humans.
A Black-and-yellow Mud Dauber (Sceliphron caementarium) observes a neighboring nest of Common Paper Wasps (Polistes exclamans).  The Common Paper Wasp, a species also known as the Guinea Paper Wasp, is a native of the southern United States.  It is currently expanding its range into the lower Susquehanna valley from the Atlantic Coastal Plain.  These two wasp species and the Pipe Organ Mud Dauber are known to regularly coexist.  All three will take advantage of man-made structures for their nest sites.  People using the picnic tables beneath this pavilion roof never noticed the hundreds of docile wasps above.
Those moody Eastern Yellowjackets (Vespula maculifrons) can get very temperamental during warm autumn days.  These wasps may appear to have no enemies, but away from areas impacted by man’s everyday activities, they do.  The Robber Fly (Promachus species) hunts like a flycatcher or other woodland bird, waiting on a perch along the forest’s edge for prey to pass by, then ambushing it, yellowjackets included.
The invasive Spotted Lanternfly, a native of eastern Asia, continues to spread destruction.  It established itself throughout much of the east side of the lower Susquehanna River during the summer and fall of 2019.  Their route of travel across the farmlands of the region intersects with plenty of vineyards to obliterate and few, if any, natural enemies.  Expect them to begin colonizing the west shore en masse during 2020.
In 2020, plan to roll a few Spotted Lanternflies over, enjoy the view, and wait for the crimson tide to pass.  With any luck, they’ll peak in a year or two.

SOURCES

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

Friendly Neighborhood Spider, Man

Within the last few years, the early-summer emergence of vast waves of mayflies has caused great consternation among residents of riverside towns and motorists who cross the bridges over the lower Susquehanna.  Fishermen and others who frequent the river are familiar with the phenomenon.  Mayflies rise from their benthic environs where they live for a year or more as an aquatic larval stage (nymph) to take flight as a short-lived adult (imago), having just one night to complete the business of mating before perishing by the following afternoon.

In 2015, an emergence on a massive scale prompted the temporary closure of the mile-long Columbia-Wrightsville bridge while a blizzard-like flight of huge mayflies reduced visibility and caused road conditions to deteriorate to the point of causing accidents.  The slimy smelly bodies of dead mayflies, probably millions of them, were removed like snow from the normally busy Lincoln Highway.  Since then, to prevent attraction of the breeding insects, lights on the bridge have been shut down from about mid-June through mid-July to cover the ten to fourteen day peak of the flight period of Hexagenia bilineata, sometimes known as the Great Brown Drake, the species that swarms the bridge.

An adult (imago) male Great Brown Drake (Hexagenia bilineata) burrowing mayfly.  Adult mayflies are also known as spinners.
A sub-adult (based on the translucence of the wings) female burrowing mayfly (Hexagenia species).  The sub-adult (subimago or dun) stage lasts less than a day.  Normally within 18 hours of leaving the water and beginning flight, it will molt into an adult, ready to breed during its final night of life.

After so many years, why did the swarms of these mayflies suddenly produce the enormous concentrations seen on this particular bridge across the lower Susquehanna?  Let’s have a look.

Following the 2015 flight, conservation organizations were quick to point out that the enormous numbers of mayflies were a positive thing—an indicator that the waters of the river were getting cleaner.  Generally, assessments of aquatic invertebrate populations are considered to be among the more reliable gauges of stream health.  But some caution is in order in this case.

Prior to the occurrence of large flights several years ago, Hexagenia bilineata was not well known among the species in the mayfly communities of the lower Susquehanna and its tributaries.  The native range of the species includes the southeastern United States and the Mississippi River watershed.  Along segments of the Mississippi, swarms such as occurred at Columbia-Wrightsville in 2015 are an annual event, sometimes showing up on local weather radar images.  These flights have been determined to be heaviest along sections of the river with muddy bottoms—the favored habitat of the burrowing Hexagenia bilineata nymph.  This preferred substrate can be found widely in the Susquehanna due to siltation, particularly behind dams, and is the exclusive bottom habitat in Lake Clarke just downstream of the Columbia-Wrightsville bridge.

Native mayflies in the Susquehanna and its tributaries generally favor clean water in cobble-bottomed streams.  Hexagenia bilineata, on the other hand, appears to have colonized the river (presumably by air) and has found a niche in segments with accumulated silt, the benthic habitats too impaired to support the native taxa formerly found there.  Large flights of burrowing mayflies do indicate that the substrate didn’t become severely polluted or eutrophic during the preceding year.  And big flights tell us that the Susquehanna ecosystem is, at least in areas with silt bottoms, favorable for colonization by the Great Brown Drake.  But large flights of Hexagenia bilineata mayflies don’t necessarily give us an indication of how well the Susquehanna ecosystem is supporting indigenous mayflies and other species of native aquatic life.  Only sustained recoveries by populations of the actual native species can tell us that.  So, it’s probably prudent to hold off on the celebrations.  We’re a long way from cleaning up this river.

In the absence of man-made lighting, male Great Brown Drakes congregate over waterways lit often by moonlight alone.  The males hover in position within a swarm, often downwind of an object in the water.  As females begin flight and pass through the swarm, they are pursued by the males in the vicinity.  The male response is apparently sight motivated—anything moving through their field of view in a straight line will trigger a pursuit.  That’s why they’re so pesky, landing on your face whenever you approach them.  Mating takes place as males rendezvous with airborne females.  The female then drops to the water surface to deposit eggs and later die—if not eaten by a fish first.  Males return to the swarm and may mate again and again.  They die by the following afternoon.  After hatching, the larvae (nymphs) burrow in the silt where they’ll grow for the coming year.  Feathery gills allow them to absorb oxygen from water passing through the U-shaped refuge they’ve excavated.

Several factors increase the likelihood of large swarms of Great Brown Drakes at bridges.  Location is, of course, a primary factor.  Bridges spanning suitable habitat will, as a minimum, experience incidental occurrences of the flying forms of the mayflies that live in the waters below.  Any extraordinarily large emergence will certainly envelop the bridge in mayflies.  Lights, both fixed and those on motor vehicles, enhance the appearance of movement on a bridge deck, thus attracting hovering swarms of male Hexagenia bilineata and other species from a greater distance, leading to larger concentrations.  Concrete walls along the road atop the bridge lure the males to try to hover in a position of refuge behind them, despite the vehicles that disturb the still air each time they pass.  The walls also function as the ultimate visual attraction as headlamp beams and shadows cast by moving vehicles are projected onto them over the length of the bridge.  Vast numbers of dead, dying, and maimed mayflies tend to accumulate along these walls for this reason.

The absence of illumination from fixed lighting on the deck of the bridge reduces the density of Great Brown Drake swarms.  Some communities take mayfly countermeasures one step further.  Along the Mississippi, some bridges are fitted with lights on the underside of the deck to attract the mayflies to the area directly over the water, concentrating the breeding mayflies and fishermen alike.  The illumination below the bridge is intended to draw mayflies away from light created by headlamps on motor vehicles passing by on the otherwise dark deck above.  Lights beneath the bridge also help prevent large numbers of mayflies from being drawn away from the water toward lights around businesses and homes in neighborhoods along the shoreline—where they can become a nuisance.

Lights out on the Columbia-Wrightsville bridge.  Dousing the lights to eliminate fixed illumination on bridges is an effective method of reducing the density of Hexagenia bilineata swarms.
With the bridge lights darkened, male Great Brown Drakes, their cellophane-like wings illuminated by headlamps to appear as white spots on the road, number in the hundreds instead of hundreds of thousands in swarms on the bridge near the east and west shorelines.
Swarms of Great Brown Drake mayflies are still present at the Columbia-Wrightsville bridge, they’re just not concentrated there in enormous numbers.  Evidence includes their bodies found in cobwebs along the entire length of the span.
The aptly-named Bridge Orb Weaver (Larinioides sclopetarius) constructs webs along the entire length of the Columbia-Wrightsville bridge, and on many of the buildings at both ends.  The abundance of victims tangled in silk must overwhelm their appetite, or maybe they actually consume only the smaller insects.  They have their choice.  Of the Bridge Orb Weaver, Uncle Ty Dyer says, “When you live along the river, it’s your friendly neighborhood spider, man.”
The native Eastern Dobsonfly (Corydalus cornutus) is among the reliable indicators of stream quality in the Susquehanna at the Columbia-Wrightsville bridge.  Winged adults, which live for about a week, are clumsy fliers attracted to lights.  The aquatic larvae are known as hellgrammites, which require clean flowing water over rocky or pebbly substrate to thrive.  Two adults were found on the bridge last evening.  It would be encouraging to find more.  Maybe we’ll stop back to have another look when the lights are back on.

SOURCES

Edsall, Thomas A.  2001.  “Burrowing Mayflies (Hexagenia) as Indicators of Ecosystem Health.”  Aquatic Ecosystem Health and Management.  43:283-292.

Fremling, Calvin R.  1960.  Biology of a Large Mayfly, Hexagenia bilineata (Say), of the Upper Mississippi River.   Research Bulletin 482.  Agricultural and Home Economics Experiment Station, Iowa State University.  Ames, Iowa.

McCafferty, W. P.  1994.  “Distributional and Classificatory Supplement to the Burrowing Mayflies (Ephemeroptera: Ephimeroidea) of the United States.”  Entomological News.  105:1-13.