As they travel between coastal wintering ranges and breeding territories in Canada and Alaska, vast numbers of shorebirds pass through the lower Susquehanna region each spring and fall—though few stop here to rest, feed, and provide us with an opportunity to observe them. Prior to the construction of man-made dams and other alterations on our lotic (flowing) waterways including the river, shorebirds took advantage of lateral bars, stream deltas, and other alluvial deposits as places to loaf and re-energize. Before they were drained and filled, some of the valley’s wetlands probably included sparsely vegetated flats where shorebirds could drop in for a brief visit. Previous to their extirpation from our region, North American Beavers were the primary providers of quality habitat for shorebirds and other migrating waders on our lotic waters. Their widespread network of dams, pools, and marshes maximized floodplain function by keeping streams thoroughly connected to their wetlands, nurturing plant communities that not only provided food and shelter for the beavers and other wildlife, but provided superb buffering against erosion while protecting against sediment and nutrient imbalances in lower Susquehanna waterways.
Beaver dams need not be large, particularly on low-gradient streams where a structure like this is sufficient to create a pool with depth adequate for building and maintaining a lodge and transporting leafy branches and other food items by water.A beaver lodge assembled in a pool with less than three feet of water, deep enough to provide the family with a measure of protection against terrestrial predators.Beaver pool ecosystems provide homes for hundreds of species of plants and animals, including migrating shorebirds and other waders.Mud flats in the margins between emergent shrubs and herbaceous plant growth attract migrating shorebirds like this Solitary Sandpiper to the abundance of invertebrate life. Seasonal movements of migrating shorebirds regularly coincide with the reductions of water levels in beaver pools which typically occur between May and September each year.During its southbound migration in September, a Least Sandpiper searches for arthropods and annelids as it visits a food-rich puddle along the periphery of a beaver pool.A Pectoral Sandpiper feeds in shallow water near a stand of Common Cattails in a beaver pool.During migration, rails including the Sora are attracted to dense emergent vegetation in beaver pools. Some will nest in these rodent-managed refugia.Green Herons visit beaver pools during migration and, due to the reliability of the food supply, will often nest in their vicinity.
So how did this happen? How did the North American Beaver become a keystone species—an animal upon which the majority of other life forms within its ecosystem are so reliant? Well, it’s largely due to the fact that our beavers aren’t particularly fond of a constant stream of noise. More specifically, they don’t like the sound of running water in places where they intend to build and maintain a lodge. And so, as they begin to place sticks, mud, limbs, stones, and other materials within a noisy riffle on a stream, they create a dam, and behind it a pool—a pool that is particularly advantageous for protecting their home and providing a means of conveyance for their construction materials and food supplies.
On a high-gradient segment of stream, beavers will create a cascading series of pools. Because water filters through a beaver dam instead of spilling over it, the work of these meticulous rodents soon silences the sounds of water changing altitude. No more sonorous riffle.Quiet please. High seasonal stream flow and damage from storms may create areas where water begins to erode the structure of the dam. Where this condition persists, an adult beaver will soon mend the breach, just to quiet things down. Why would beavers demand such a hush upon their domain? Well, they have poor eyesight, but their hearing is excellent, and they rely upon it to detect danger.The Louisiana Waterthrush (Parkesia motacilla), one of our earliest-arriving warblers, nests in forests along clear, high-gradient streams. In mid-April, we found this individual and three others squabbling over a breeding territory adjacent to the series of cascading beaver pools shown in the previous images.Native denizens of coldwater streams, neither the Brook Trout nor the Eastern Blacknose Dace has any difficulty finding its way through the voids in beaver dams to ascend and descend the sequence of pools.On a low-gradient segment of stream, a dam just over a foot in height may be sufficient to create a beaver pool of considerable size. Resembling the water-logged muskeg of the far north, well-established beaver pools form boggy habitats familiar to migrating shorebirds.Water levels in the pools usually drop along with the stream’s base flow as soon as the effects of the spring thaw and rain showers subside. Feeding areas in shallow water and on muddy ground are often revealed just in time for northbound shorebirds and other waders to stop by in late April and May. These conditions often persist through the growing season and the fall migration of these birds which begins as early as late June and sometimes extends into October.Where the pool inundates standing timber such as Red Maple and other species not used by beavers, the dead snags provide vital feeding areas for birds and other wildlife. Cavity nesters like this Tree Swallow seldom find suitable natural housing elsewhere.The mosaic of marshlands and braided stream channels within the beaver pool complex supports an abundance of aquatic life including these breeding Eastern Newts, seen here surrounded by the exuvia left behind following a massive hatch of alderflies (Sialinae). Alderflies are a stream inhabitant during their larval stage and are indicator of clean water conditions.A modern-day example of the way fully functional stream floodplains used to look in the Lower Susquehanna River Watershed. Though the pools may appear pond-like during the cooler and wetter months of the year, by summer the water levels behind the beaver dams recede as the base flow of the stream wanes. Now the true nature of the marsh, shallow pool, and braided stream complex is revealed. Unlike most man-made dams that set a fixed pool elevation regardless of flow by discharging water over the top of the structure or through a spillway or gate, beaver dams merely throttle the flow through their porous construction. Unless the beaver begins plugging small leaks as fast as the stream flow ebbs, the water level in the pools will drop. So they’re not left high and dry, lodges are located in the deepest pools, usually in close proximity to the dam and/or one of the stream courses. Though not inundated during the dry season, the soil in the pool complex is almost always damp and plants grow vigorously there, sequestering nutrients and retaining sediments in beneficial deposition patterns that actually inhibit erosion of the riparian landscape. These streams and floodplains retain their hyporheic zone and freely exchange water with the underlying water table and aquifer. It’s the ultimate floodplain management system, and the beavers don’t even know their doing all the work. (Google Maps base image)Where another high-gradient segment of stream enters the main pool complex, beavers have created an additional series of cascading pools. The impoundments created by these dams help diffuse stormwater energy and process more nutrients and sediments within the floodplain’s wetland vegetation system. (Google Maps base image)Beaver pools often refill as stream flows increase following autumn rains. The stockpiles of vegetative foods that grew within the beaver’s domain through the summer then become flooded and are a prime source of nutrition for not only the beavers, but waterfowl during both their autumn and spring migrations. Gleaning and probing Sandhill Cranes often find these habitats to their liking as well.
While North American Beavers have returned to the region, most live as “bank beavers”, residing in the river and larger creeks of the valley where they excavate shelters among the roots of Black Willows and other shoreline trees and shrubs. Floodplain encroachment, legacy sediment deposits, and just plain human intolerance have all conspired to prohibit North American Beavers from performing their magic on smaller local streams. For migrating shorebirds, this continued absence of beaver dam ecosystems has turned much of the lower Susquehanna valley into “flyover country”. Those travelers that do stop to rest and feed concentrate at the few favorable locations such as the lateral bars and the hydroelectric dam-created delta at the Conejohela Flats on the river in Lancaster County. But centralization has its drawbacks. Migrants spending time at concentration points may have a greater chance of contracting and spreading disease. Protracted heavy foraging can degrade these habitats. And over time, features such the lateral bars and delta deposits, including those on the Conejohela Flats, transition into other habitats—riparian forests. A more widespread selection of favorable stopover points for shorebirds, waders, waterfowl, and other migrants is certainly desirable.
IMITATION IS THE SINCEREST FORM OF FLATTERY
Until public sentiment sways in favor of the North American Beaver, wildlife managers are mimicking some of the attributes of their sound-inspired installations.
Created by excavating a depression in heavy clay soils, this new impoundment at the Pennsylvania Game Commission’s Middle Creek Wildlife Management Area collects water directly from rainfall and from surface runoff. Its depth at no point is greater than about two or three feet. During the driest times of the year, this space will be a mudflat, and a haven for migrating shorebirds.
Shallow-water conservation impoundments designed, constructed, and managed for migratory waterfowl and waders including shorebirds are not what we typically refer to as ponds—though they are lentic (still) waters. Similar shallow freshwater impoundments at our National Wildlife Refuges are referred to as pools by the United States Fish and Wildlife Service, but smaller versions like this example at Middle Creek very closely resemble the prairie potholes created by glacial scour in the north-central United States and adjacent portions of Canada. Many populations of migratory birds are familiar with pothole ecosystems and, like the beaver pools and marshes, have relied upon them as waypoints along their journeys for centuries.
Impoundments most beneficial to migrating waterfowl and waders including shorebirds are shallow in depth. They lack the deeper waters of a pond or lake and thus have no limnetic (open water) or aphotic zones. Managed throughout as a littoral zone, impoundments grow plants in shallow water or on damp soil through the summer months to chew up nutrients accumulated in waste deposited by visiting birds. This vegetation is then flooded from late fall through early spring as forage habitat for migratory waterfowl. The timing of the fluctuations in water levels approximates those of the beaver pools and marshes on lotic (flowing) waters.A gate assembly is a water control structure installed to provide seasonal management of the water levels in a conservation impoundment. More than once, beavers have heard the sounds of tumbling waters inside these types of devices and tried to dam them up!
You’ve heard the line, “If you build it, they will come.” Well, it’s true. Here is a sample of the activity witnessed during the past two weeks at the new impoundment completed just several months ago at Middle Creek Wildlife Management Area along the tour route just beyond the “Stop 3” overlook.
The ubiquitous Snow Geese were among the first migratory occupants of the new impoundment. A few are currently lingering in the vicinity.Ducks soon followed. These Blue-winged Teal were among the last to pass through earlier this month.Wilson’s Snipe were among the first species of migratory shorebirds to visit the new impoundment at Middle Creek……as were Killdeer, a species which nests nearby.Then, earlier this month, flocks of shorebirds including these Least Sandpipers were arriving to feed and rest.Least Sandpipers search for small invertebrates in shallow water and exposed soil.A Least Sandpiper (left) and a Semipalmated Sandpiper (right).Not all shorebirds seen by themselves are alone, and that includes the Solitary Sandpiper.Here’s a Solitary Sandpiper (right) feeding alongside a Least Sandpiper (center) and a White-rumped Sandpiper (left).A Least Sandpiper (left) and a White-rumped Sandpiper (right).Rare in our area during spring, the White-rumped Sandpiper (Calidris fuscicollis) flies north using the central flyway, then heads south along the Atlantic flyway in the fall, when it tends to be more regular here.Rocking and teetering along as it looks for food, the Spotted Sandpiper may be one of the easiest of shorebirds to identify.Chunky little Dunlin (Calidris alpina) with their conspicuously down-curved bills are another easy-to-identify species, particularly in the spring when their breeding (alternate) plumage includes a black belly.Black-bellied Plovers acquire a handsome set of plumage in the spring as well.Killdeer too are plovers and this pair appears to have taken up residence on barren ground along the periphery of the new impoundment.The Semipalmated Plover doesn’t have nearly the flair for ornament its close relatives the Killdeer do; these little shorebirds wear only one ring around their neck instead of two. Think this plover is cute?,……then check out this newly hatched Killdeer. It starts life with just one necklace too, but acquires a second as it grows. Look at those legs! (If you visit the new impoundment at Middle Creek, drive slowly and please watch where you’re going. Baby Killdeer and other young birds, as well as mammals and turtles, are commonly crossing the paved surfaces right now.)Speaking of legs, here’s one of dozens of Lesser Yellowlegs that visited the new impoundment during their recent northbound travels.Though less numerous than the smaller Lesser Yellowlegs, a Greater Yellowlegs seldom goes unnoticed when dropping by the man-made pothole habitat.Have trouble telling a Greater Yellowlegs like this one from a Lesser Yellowlegs? Look for the heavier, longer bill on the former, as well as dark barring along its flanks below the wings while the bird is in breeding (alternate) plumage during the spring migration.Everyone likes to see something unusual every now and then, and this impoundment delivers. Just yesterday, we photographed this migrating Wilson’s Phalarope (top center) among two Least Sandpipers (top left and right), a Lesser Yellowlegs (left and slightly forward of the phalarope), and a White-rumped Sandpiper (foreground).Renowned for spinning in circles as they feed in shallow water, Wilson’s Phalaropes (Phalaropus tricolor) passing through the lower Susquehanna basin are headed toward nesting areas in the prairie wetlands, including potholes, of the northern United States and adjacent sections of southern Canada.
Species of wildlife in addition to shorebirds and waterfowl have already found the new impoundment favorable…
Pairs of breeding Spot-winged Gliders (Pantala hymenaea), seen here in tandem while ovipositing, were swarming the impoundment after arriving earlier this week. These dragonflies are ofttimes unpredictable nomads and are similar in appearance to the usually more numerous Wandering Gliders. To recolonize seasonal portions of their range, both are famous for hitching a ride en masse on storm systems. They share the behavior of finding ephemeral and new bodies of water favorable for egg laying due to their low density of aquatic predators.We watched this Snapping Turtle arrive to apparently find the newly created waters to its liking. Snapping Turtles are important consumers in a wetland ecosystem. Larger specimens may fill the role of an upper trophic level or apex predator, eliminating vulnerable mid-level consumers including other Snapping Turtles.Because it bounces its tail up and down like a Spotted Sandpiper, you may at first glance mistake an American Pipit for a shorebird. Long known as the Water Pipit, these songbirds have been visiting the impoundment while migrating north and stopping to feed in nearby croplands.Seen here with Least Sandpipers is a visiting Glossy Ibis.Sometimes twenty or more of these mostly coastal waders have made a pit stop at the “new Middle Creek pothole”, though none have thus far chosen to remain long. Apparently, food sources sufficient to sustain a bird of their size have yet to develop in its benthos.Western Cattle Egrets visiting Middle Creek this spring have been frequenting the new impoundment.With still little in the way of insects such as grasshoppers available in the surrounding landscape,……cattle egrets are looking to find prey like this Green Frog.Many have been observed hunting the adjacent grasslands..Where small mammals, mostly Meadow Voles, are being taken in abundance.
Managing saturation levels in shallow-water impoundments to resemble the seasonal variations in beaver pool and marsh systems can create lush growth and wildlife-rich environments. Take a look at some images from a project in a headwaters area of a tributary to Conewago Creek (west)…
By late July, southbound shorebirds were already using these mudflats to feed and rest. Other sections of the impoundment were dense with emergent and aquatic plants, the latter kept hydrated in deeper pools of the project by the inflow from several captured springs that supplement direct rainfall and sheet runoff to supply its water. During a seasonal drawdown, the exposure of the impoundment’s soils to direct sunlight can provide a measure of disinfection to reduce the chances of disease transmission among its populations of visiting birds and other animals.In the deeper pools of the impoundment, water lilies and other aquatic plants grow in lush mats to provide cover and feeding areas for resident populations of breeding reptiles and amphibians.An abundance of foods are available for waders including this Green Heron……and this immature Little Blue Heron, a wanderer typical of more southern latitudes.While walking the road among tall grasses in the supporting landscape surrounding this impoundment, we were at first startled when these Sandhill Cranes strode by going the other direction. We quietly kept moving,……then spotted them again as we looked across the impoundment to realize they weren’t alone, but were escorting a colt.The hatching of this colt is testimony to the vital role wetland ecosystems play in the lives of hundreds of species. Whether they be beaver pools and marshes on lotic waters or man-made shallow lentic waters, each of these habitats is filling a void that left floodplains and other critical lowland biomes faltering. While they can’t replace the full-function floodplain management provided by an active beaver colony, shallow-water impoundments can provide relief for habitat-starved populations of the animals and plants that rely upon them. A constellation of these projects on lands public or private across the lower Susquehanna watershed could help provide refuge for many of our flora and fauna with the most desperately fragmented of ranges.
So that you can relax while observing the comings and goings at a pair of the lower Susquehanna valley’s man-made impoundments, the Pennsylvania Game Commission has erected two viewing pavilions for public use on its lands…
The Haldeman Island observation pavilion is located on State Game Lands 290 just upstream from the Juniata River’s mouth on the Susquehanna at Clark’s Ferry in Dauphin County.It overlooks not only the island’s man-made shallow-water impoundments and neighboring grasslands, but the tower used in the 1970s to reintroduce Bald Eagles from Saskatchewan to the lower Susquehanna. Interpretive signs explain the conservation stories of habitats and the eagle reintroduction program.The observation pavilion at Middle Creek Wildlife Management Area is of similar construction to the one at Haldeman Island. It is accessed from the parking pull-off along the tour road at its intersection with Chapel Road, just before the right turn and incline that leads to the “Stop 3” grassland overlook.It too includes numerous interpretive signs to help visitors understand impoundment management.
During the next two weeks, the exodus of migrating shorebirds now staged and feeding upon Atlantic Horseshoe Crab eggs on Delaware Bay will commence. During the evening of their departure from the bay, many of these birds cross portions of the Lower Susquehanna River Watershed, particularly east of the river. Stormy weather and other climatic conditions may force some of them to seek a place to put down temporarily, so keeping a close eye on the new pothole-like impoundment at Middle Creek may be a prudent move. After that, waders known as “post-breeding wanderers” can show up at any time. Then, beginning as early as late June, shorebirds begin moving south on a migration that can provide us with viewing opportunities into September and beyond. See you out there!
Numbers and varieties of northbound Neotropical songbirds and shorebirds are presently reaching their peak in the Lower Susquehanna River Watershed. Upon arrival, those species that breed locally will begin protecting a home range without delay. These Lesser Yellowlegs on the other hand will ultimately defend nesting sites in boreal forests far to our north, but they can still become spectacularly aggressive toward one another while passing through. During coming weeks, expect birds of reproductive age to demonstrate a similar demeanor, especially the males. You won’t want to miss the handsome plumage, the songs, and the territorial behaviors of migratory birds in May. It’s a big part of what makes them so worthy of our best efforts to appreciate and protect them.
It may seem hard to believe, but the autumn migration of shorebirds and many Neotropical songbirds is now well underway. To see the former in what we hope will be large numbers in good light, we timed a visit to the man-made freshwater impoundments at Bombay Hook National Wildlife Refuge near Smyrna, Delaware, to coincide with a high-tide during the mid-morning hours. Come along for a closer look…
Along a large portion of its route, the tour road at Bombay Hook N.W.R. sits atop the man-made dikes that create several sizeable freshwater pools (left) along the inland border of one of the largest remaining salt marsh estuaries in the Mid-Atlantic States (right).Twice daily, the rising tide from Delaware Bay flows along the tidal creeks to flood Bombay Hook’s extensive marshes.At high tide, mudflats in Bombay Hook’s coastal estuary become inundated by salt water, forcing migratory shorebirds to relocate to bay side beaches or other higher ground to rest and feed for several hours.At Bombay Hook, migratory shorebirds, waterfowl, and waders can find refuge from high tide in the freshwater impoundments created by capturing water along the inland west side of a system of earthen dikes.Mechanical or stacked-board gate systems are used to control water depth in the impoundments. Levels can be adjusted seasonally to manage plant growth and create conditions favorable for use by specific groups of birds and other wildlife.A map at Shearness Pool, the largest impoundment on the refuge, shows the location of other freshwater pools at Bombay Hook.A mix of mudflats and shallow water on Raymond Pool provides ideal habitat for a variety of shorebirds forced from the vast tidal marshes by the rising tide. For us, a mid-morning high tide places these birds in perfect light as they feed and loaf in the pools to the west of the tour road located atop the dikes.Migrating shorebirds arrive on Raymond Pool to find refuge from the rising tide to the east. Showing a single ring around their breast, many Semipalmated Plovers can be seen here among the Semipalmated Sandpipers, the latter the most abundant shorebird presently populating Bombay Hook. Feeding in deeper water in the background are Short-billed Dowitchers. All of these birds consume a variety of invertebrates they find both in and on the mud.Semipalmated Plovers and Semipalmated Sandpipers arriving on a mudflat at Raymond Pool.A Short-billed Dowitcher glides in from the salt marsh to visit the shallows of Raymond Pool for a couple of hours.A Short-billed Dowitcher feeding among Semipalmated Plovers and Semipalmated Sandpipers.Short-billed Dowitchers in water almost too deep for the Semipalmated Sandpipers in their company.A lone Black-bellied Plover (Pluvialis squatarola) among the abundance of Short-billed Dowitchers.Short-billed Dowitchers probe the mud with their sewing machine-like feeding style.Seldom do they take a break long enough for an observer to their bill in its entirety.A Lesser Yellowlegs arrives at Raymond Pool as a high-tide refugee.Another Lesser Yellowlegs on a mudflat.A Greater Yellowlegs wades into shallow water to feed.It’s difficult to estimate just how many Semipalmated Plovers and Semipalmated Sandpipers were seen. There were at least 500 plovers, and they were very vocal. The latter species was present in numbers measurable in the thousands. We don’t think 10,000 Semipalmated Sandpipers is an overestimate.Searching through the Semipalmated Sandpipers, one could regularly find a very similar species among them.We identified the longer-billed and slightly larger Western Sandpiper (Calidris mauri) and found the species to be present possibly by the hundreds among the masses of thousands of Semipalmated Sandpipers. These seem to be unusually high numbers for this more western species, but who’s complaining?As we sifted through these groups of tiny shorebirds known as “peeps”, we found Western Sandpipers (top) regularly distributed among the multitudes of Semipalmated Sandpipers (bottom) we encountered.A Western Sandpiper (top) photographed with a Semipalmated Sandpiper (bottom) in Bear Swamp Pool.Of course, shorebirds aren’t all there is to see at Bombay Hook. More than 100 Snowy Egrets were found on the freshwater pools alongside birds like this Semipalmated Plover.Great Egrets could be seen stalking small fish in the channels of the pools.And a few Green Herons were found lurking in the vegetation.This Osprey briefly startled the shorebirds on Raymond Pool until they realized it posed no threat.By early afternoon, we noticed the tide beginning to retreat from the saltwater marsh and mudflats opposite Shearness Pool. As shorebirds began returning there to feed, we decided to make our way to Raymond Pool to watch the exodus.With the high tide receding from the coastal estuary back into Delaware Bay, shorebirds promptly departed their concentrated environs on Raymond Pool to spread out over thousands of acres of salt marsh to feed.More shorebirds exit Raymond Pool en route to the adjacent tidal areas to feed. This outbound group includes two Black-bellied Plovers (top center and four birds to the right).These migrants have just begun their autumn journey from breeding grounds in Canada and Alaska to wintering areas located as far south as southern South America. For them, Bombay Hook and other refuges are irreplaceable feeding and resting locations to help them refuel for their long journey ahead. For them, a little vacation along the coast is a matter of life and death.A goodwill ambassador bids us farewell at the end of our visit to Bombay Hook. Remember to support your National Wildlife Refuges by purchasing your annual Federal Duck Stamp. They’re available right now at your local United States Post Office, at the Bombay Hook visitor’s center, or online at the United States Fish and Wildlife Service website.
Planning a visit? Here are some upcoming dates with morning high tides to coax the birds out of the tidal estuary and into good light in the freshwater impoundments on the west side of the tour road…
Tuesday, August 19 at approximately 07:00 AM EDT
Wednesday, August 20 at approximately 08:00 AM EDT
At Lake Redman just to the south of York, Pennsylvania, a draw down to provide drinking water to the city while maintenance is being performed on the dam at neighboring Lake Williams, York’s primary water source, has fortuitously coincided with autumn shorebird migration. Here’s a sample of the numerous sandpipers and plovers seen today on the mudflats that have been exposed at the southeast end of the lake…
One of a hundred or more Least Sandpipers seen on mudflats at Lake Redman today.A Semipalmated Plover and a Least SandpiperPectoral Sandpipers.A Pectoral Sandpiper and two Least Sandpipers.A Semipalmated Sandpiper.A Stilt Sandpiper feeding.Stilt Sandpiper consuming an edible.Stilt Sandpiper at rest.A Solitary SandpiperA Lesser Yellowlegs.A Greater Yellowlegs.Stirring up the shorebird crowd every now and then were several Ospreys, but all would soon be back to the business of feeding in the mud.An Osprey hovers above shallow water near the mudflats as it searches for fish.
Not photographed but present at Lake Redman were at least two additional species of shorebirds, Killdeer and Spotted Sandpiper—bringing the day’s tally to ten. Not bad for an inland location! It’s clearly evident that these waders overfly the lower Susquehanna valley in great numbers during migration and are in urgent need of undisturbed habitat for making stopovers to feed and rest so that they might improve their chances of surviving the long journey ahead of them. Mud is indeed a much needed refuge.
Your best bet for finding migrating shorebirds in the lower Susquehanna region is certainly a visit to a sandbar or mudflat in the river. The Conejohela Flats off Washington Boro just south of Columbia is a renowned location. Some man-made lakes including the one at Middle Creek Wildlife Management Area are purposely drawn down during the weeks of fall migration to provide exposed mud and silt for feeding and resting sandpipers and plovers. But with the Susquehanna running high due to recent rains and the cost of fuel trending high as well, maybe you want to stay closer to home to do your observing.
Fortunately for us, migratory shorebirds will drop in on almost any biologically active pool of shallow water and mud that they happen to find. This includes flooded portions of fields, construction sites, and especially stormwater retention basins. We stopped by a new basin just west of Hershey, Pennsylvania, and found more than two dozen shorebirds feeding and loafing there. We took each of these photographs from the sidewalk paralleling the south shore of the pool, thus never flushing or disturbing a single bird.
Designed to prevent stream flooding and pollution, this recently installed stormwater retention basin along US 322 west of Hershey, Pennsylvania, has already attracted a variety of migrating plovers and sandpipers.Killdeer stick close to exposed mud as they feed.Two of more than a dozen Least Sandpipers found busily feeding in the inch-deep water.A Lesser Yellowlegs searching for small invertebrates.Two Lesser Yellowlegs work out a disagreement.Male Twelve-spotted Skimmers patrol the airspace above a pair of Least Sandpipers. Dragonflies and other aquatic insects are quick to colonize the waters held in well-engineered retention basins. Proper construction and establishment of a functioning food chain/web in these man-made wetlands prevents them from becoming merely temporary cesspools for breeding mosquitos.
So don’t just drive by those big puddles, stop and have a look. You never know what you might find.
A Semipalmated Sandpiper (middle right) joins a flock of Least Sandpipers.Pectoral Sandpipers (two birds in the center) are regular fall migrants on the Susquehanna at this time of year. They are most frequently seen on gravel and sand bars adjacent to the river’s grassy islands, but unusually high water for this time of year prevents them from using this favored habitat. As a result, you might be lucky enough to discover Pectoral Sandpipers on almost any mudflat in the area.Two Pectoral Sandpipers and five smaller, but otherwise very similar, Least Sandpipers.A Killdeer (right), a Semipalmated Plover (upper right), and Least and Pectoral Sandpipers (left).
Have you purchased your 2023-2024 Federal Duck Stamp? Nearly every penny of the 25 dollars you spend for a duck stamp goes toward habitat acquisition and improvements for waterfowl and the hundreds of other animal species that use wetlands for breeding, feeding, and as migration stopover points. Duck stamps aren’t just for hunters, purchasers get free admission to National Wildlife Refuges all over the United States. So do something good for conservation—stop by your local post office and get your Federal Duck Stamp.
Your Federal Duck Stamp is your admission ticket for entry into many of the country’s National Wildlife Refuges including Bombay Hook National Wildlife Refuge on Delaware Bay near Smyrna, Delaware.
Still not convinced that a Federal Duck Stamp is worth the money? Well then, follow along as we take a photo tour of Bombay Hook National Wildlife Refuge. Numbers of southbound shorebirds are on the rise in the refuge’s saltwater marshes and freshwater pools, so we timed a visit earlier this week to coincide with a late-morning high tide.
This pair of Northern Bobwhite, a species now extirpated from the Lower Susquehanna River Watershed and the rest of Pennsylvania, escorted us into the refuge. At Bombay Hook, they don’t waste your money mowing grass. Instead, a mosaic of warm-season grasses and early successional growth creates ideal habitat for Northern Bobwhite and other wildlife.Twice each day, high tide inundates mudflats in the saltwater tidal marshes at Bombay Hook prompting shorebirds to move into the four man-made freshwater pools. Birds there can often be observed at close range. The auto tour route through the refuge primarily follows a path atop the dikes that create these freshwater pools. Morning light is best when viewing birds on the freshwater side of the road, late-afternoon light is best for observing birds on the tidal saltwater side.A Great Blue Heron at high tide on the edge of a tidal creek that borders Bombay Hook’s tour route at Raymond Pool.Semipalmated Sandpipers stream into Raymond Pool to escape the rising tide in the salt marsh.More Semipalmated Sandpipers and a single Short-billed Dowitcher (Limnodromus griseus) arrive at Raymond Pool.Two more Short-billed Dowitchers on the way in.Recent rains have flooded some of the mudflats in Bombay Hook’s freshwater pools. During our visit, birds were often clustered in areas where bare ground was exposed or where water was shallow enough to feed. Here, Short-billed Dowitchers in the foreground wade in deeper water to probe the bottom while Semipalmated Sandpipers arrive to feed along the pool’s edge. Mallards, American Avocets, and egrets are gathered on the shore.More Short-billed Dowitchers arriving to feed in Raymond Pool.Hundreds of Semipalmated Sandpipers gathered in shallow water where mudflats are usually exposed during mid-summer in Raymond Pool.Hundreds of Semipalmated Sandpipers, several Short-billed Dowitchers, and some Forster’s Terns (Sterna forsteri) crowd onto a mud bar at Bear Swamp Pool.A zoomed-in view of the previous image showing a tightly packed crowd of Semipalmated Sandpipers, Forster’s Terns, and a Short-billed Dowitcher (upper left).Short-billed Dowitchers wading to feed in the unusually high waters of Raymond Pool.Short-billed Dowitchers, American Avocets, and a Snowy Egret in Raymond Pool. A single Stilt Sandpiper (Calidris himantopus) can been seen flying near the top of the flock of dowitchers just below the egret.Zoomed-in view of a Stilt Sandpiper (Calidris himantopus), the bird with white wing linings.American Avocets probe the muddy bottom of Raymond Pool.Among these Short-billed Dowitchers, the second bird from the bottom is a Dunlin. This sandpiper, still in breeding plumage, is a little bit early. Many migrating Dunlin linger at Bombay Hook into October and even November.This Least Sandpiper found a nice little feeding area all to itself at Bear Swamp Pool.Lesser Yellowlegs at Bear Swamp Pool.Lesser Yellowlegs at Bear Swamp PoolA Greater Yellowlegs at Bear Swamp Pool.A Caspian Tern patrolling Raymond Pool.The chattering notes of the Marsh Wren’s (Cistothorus palustris) song can be heard along the tour road wherever it borders tidal waters.This dome-shaped Marsh Wren nest is supported by the stems of Saltwater Cordgrass (Sporobolus alterniflorus), a plant also known as Smooth Cordgrass. High tide licks at the roots of the cordgrass supporting the temporary domicile.By far the most common dragonfly at Bombay Hook is the Seaside Dragonlet (Erythrodiplax berenice). It is our only dragonfly able to breed in saltwater. Seaside Dragonlets are in constant view along the impoundment dikes in the refuge.Red-winged Blackbirds are still nesting at Bombay Hook, probably tending a second brood.Look up! A migrating Bobolink passes over the dike at Shearness Pool.Non-native Mute Swans and resident-type Canada Geese in the rain-swollen Shearness Pool.A pair of Trumpeter Swans (Cygnus buccinator) as seen from the observation tower at Shearness Pool. Unlike gregarious Tundra and Mute Swans, pairs of Trumpeter Swans prefer to nest alone, one pair to a pond, lake, or sluggish stretch of river. The range of these enormous birds was restricted to western North America and their numbers were believed to be as low as 70 birds during the early twentieth century. An isolated population consisting of several thousand birds was discovered in a remote area of Alaska during the 1930s allowing conservation practices to protect and restore their numbers. Trumpeter Swans are slowly repopulating scattered east coast locations following recent re-introduction into suitable habitats in the Great Lakes region.A Great Egret prowling Shearness Pool.A Snowy Egret in Bear Swamp Pool.Wood Ducks in Bear Swamp Pool.A Bombay Hook N.W.R. specialty, a Black-necked Stilt and young at Bear Swamp Pool.
As the tide recedes, shorebirds leave the freshwater pools to begin feeding on the vast mudflats exposed within the saltwater marshes. Most birds are far from view, but that won’t stop a dedicated observer from finding other spectacular creatures on the bay side of the tour route road.
Bombay Hook National Wildlife Refuge protects a vast parcel of tidal salt marsh and an extensive network of tidal creeks. These areas are not only essential wildlife habitat, but are critical components for maintaining water quality in Delaware Bay and the Atlantic.The shells of expired Atlantic Horseshoe Crabs were formerly widespread and common among the naturally occurring flotsam along the high tide line on Delaware Bay. We found just this one during our visit to Bombay Hook. Man has certainly decimated populations of this ancient crustacean during recent decades.As the tide goes out, it’s a good time for a quick walk into the salt marsh on the boardwalk trail opposite Raymond Pool.Among the Saltmarsh Cordgrass along the trail and on the banks of the tidal creek there, a visitor will find thousands and thousands of Atlantic Marsh Fiddler Crabs (Minuca pugnax).Atlantic Marsh Fiddler Crabs and their extensive system of burrows help prevent the compaction of tidal soils and thus help maintain ideal conditions for the pure stands of Saltwater Cordgrass that trap sediments and sequester nutrients in coastal wetlands.A male Atlantic Marsh Fiddler Crab peers from its den.Herons and egrets including this Great Egret are quite fond of fiddler crabs. As the tide goes out, many will venture away from the freshwater pools into the salt marshes to find them.A Green Heron seen just before descending into the cordgrass to find fiddler crabs for dinner.A juvenile Clapper Rail (Rallus crepitans crepitans) emerges from the cover of the cordgrass along a tidal creek to search for a meal.Glossy Ibis leave their high-tide hiding place in Shearness Pool to head out into the tidal marshes for the afternoon.Great Black-backed Gulls, Herring Gulls, and possibly other species feed on the mudflats exposed by low tide in the marshes opposite Shearness Pool.An Osprey patrols the vast tidal areas opposite Shearness Pool.
No visit to Bombay Hook is complete without at least a quick loop through the upland habitats at the far end of the tour route.
Indigo Buntings nest in areas of successional growth and yes, that is a Spotted Lanternfly on the grape vine at the far right side of the image.Blue Grosbeaks (Passerina caerulea) are common nesting birds at Bombay Hook. This one was in shrubby growth along the dike at the north end of Shearness Pool.These two native vines are widespread at Bombay Hook and are an excellent source of food for birds. The orange flowers of the Trumpet Vine are a hummingbird favorite and the Poison Ivy provides berries for numerous species of wintering birds.The Pileated Woodpecker is one of the numerous birds that supplements its diet with Poison Ivy berries. The tree this individual is visiting is an American Sweetgum (Liquidambar styraciflua), a species native to the Atlantic Coastal Plain in Delaware. The seed balls are a favorite winter food of goldfinches and siskins.Finis Pool has no frontage on the tidal marsh but is still worth a visit. It lies along a spur road on the tour route and is located within a deciduous coastal plain forest. Check the waters there for basking turtles like this giant Northern Red-bellied Cooter (Pseudemys rubiventris) and much smaller Painted Turtle.The White-tailed Deity is common along the road to Finis Pool.Fowler’s Toads (Anaxyrus fowleri) breed in the vernal ponds found in the vicinity of Finis Pool and elsewhere throughout the refuge.The National Wildlife Refuge System not only protects animal species, it sustains rare and unusual plants as well. This beauty is a Turk’s Cap Lily (Lilium superbum), a native wildflower of wet woods and swamps.Just as quail led us into the refuge this morning, this Wild Turkey did us the courtesy of leading us to the way out in the afternoon.
We hope you’ve been convinced to visit Bombay Hook National Wildlife Refuge sometime soon. And we hope too that you’ll help fund additional conservation acquisitions and improvements by visiting your local post office and buying a Federal Duck Stamp.
Visitors stopping by Middle Creek Wildlife Management Area this week found yet another post-breeding wanderer feeding in the shallows of the main lake and adjacent pond along Hopeland Road—a juvenile Little Blue Heron.
The juvenile Little Blue Heron is a white bird resembling an egret during its first year. At about one year of age, it begins molt into a deep blue adult plumage. Young birds are notorious for roaming inland and north from breeding areas along the Atlantic coast and throughout the south. They are a post-breeding wanderer nowhere near as rare as the Limpkin seen at Middle Creek a week ago; a few are found each summer in the Lower Susquehanna River Watershed.
A juvenile Little Blue Heron currently at Middle Creek Wildlife Management Area. Note the yellow legs and pale beak, field marks that help separate this species from the Great Egret and Snowy Egret.
As oft times happens, birders attracted to see one unusual bird find another in the vicinity. So with fall shorebird migration ramping up, the discovery of something out of the ordinary isn’t a total surprise, particularly where habitat is good and people are watching.
A Hudsonian Godwit (Limosa haemastica) has arrived on mudflats at Middle Creek Wildlife Management Area.
The arrival of a Hudsonian Godwit is not an unheard of occurrence in the lower Susquehanna region, but locating one that sticks around and provides abundant viewing opportunities is a rarity. This adult presumably left the species’ breeding areas in Alaska or central/western Canada in recent weeks to begin its southbound movement. Hudsonian Godwits pass through the eastern United States only during the autumn migration, and the majority fly by without being noticed along a route that mostly takes them offshore of the Mid-Atlantic States.
The Hudsonian Godwit (right) at Middle Creek W.M.A. feeding with other migrating shorebirds…a Lesser Yellowlegs (top) and a Least Sandpiper (left).To probe the muddy bottom for invertebrates, Hudsonian Godwits will often wade in deeper water than accompanying species.This godwit seemed to be capturing small snails, presumably the young of the thousands of adult Acute Bladder Snails (Physellla acuta) seen here covering the surface of the mud. This species of air-breathing freshwater snail is tolerant of low levels of dissolved oxygen and is frequently the only mollusk found in polluted waters of the lower Susquehanna valley.For feeding shorebirds, the young snails may be more edible than the adults due to their fragile shells. Small birds like the Least Sandpiper may also be consuming the gelatinous egg masses. In North America, the Acute Bladder Snail was believed to be an introduced species from Europe. DNA testing has now determined that it is actually a native species that was instead transported into Europe from North America early in the nineteenth century or before. Locally, the snails were known as Physella heterostropha and were thought to be native. However, the recent genetic tests have shown Physella heterostropha and Physella integra, a snail first described by Lancaster County naturalist Samuel S. Haldeman, to be synonyms of Physella acuta. Click the “Freshwater Snails” tab at the top of this page to learn more about these mollusks.The Hudsonian Godwit at Middle Creek W.M.A., you may never get a better look!
Late August and early September is prime time to see migrating shorebirds as they pass through the lower Susquehanna valley during their autumn migration, which, believe it or not, can begin as early as late June. These species that are often assumed to spend their lives only near the seashore are regular visitors each fall as they make their way from breeding grounds in the interior of Canada to wintering sites in seacoast wetlands—many traveling as far south as Central and South America.
Low water levels on the Susquehanna River often coincide with the shorebird migration each year, exposing gravel and sand bars as well as vast expanses of muddy shorelines as feeding and resting areas for these traveling birds. This week though, rain from the remnants of Tropical Storm Fred arrived to increase the flow in the Susquehanna and inundate most of the natural habitat for shorebirds. Those on the move must either continue through the area without stopping or find alternate locations to loaf and find food.
The draining and filling of wetlands along the river and elsewhere in the region has left few naturally-occurring options. The Conejohela Flats south of Columbia offer refuge to many migrating sandpipers and their allies, the river level there being controlled by releases from the Safe Harbor Dam during all but the severest of floods. Shorebirds will sometimes visit flooded fields, but wide-open puddles and farmland resembling mudflats is more of springtime occurrence—preceding the planting and growth of crops. Well-designed stormwater holding facilities can function as habitat for sandpipers and other wildlife. They are worth checking on a regular basis—you never know what might drop in.
Right now, there is a new shorebird hot spot in the Lower Susquehanna River Watershed—Middle Creek Wildlife Management Area. The water level in the main impoundment there has been drawn down during recent weeks to expose mudflats along the periphery of nearly the entire lake. Viewing from “Stop 1” (the roadside section of the lake in front of the refuge museum) is best. The variety of species and their numbers can change throughout the day as birds filter in and out—at times traveling to other mudflats around the lake where they are hidden from view. The birds at “Stop 1” are backlit in the morning with favorable illumination developing in the afternoon.
Have a look at a few of the shorebirds currently being seen at Middle Creek…
The Killdeer is familiar as a breeding bird in the lower Susquehanna region. Large numbers can congregate ahead of and during migration on mudflats and gravel bars.The Least Sandpiper is one of the “peeps”, a group of very small shorebirds. This species is quite common at Middle Creek right now. Note the plants beginning to grow in the mud. Later in the fall, after the shorebirds are gone, raising the water level in the lake will flood these newly vegetated areas to provide an abundance of food for migrating waterfowl. This cycle can be repeated annually to support transient birds during what is often the most vulnerable time of their lives…fall migration.The Baird’s Sandpiper (Calidris bairdii) is an uncommon “peep” along the east coast during autumn migration. On the lower Susquehanna it is most frequently encountered on the vegetated gravel bars in mid-river during the last days of August or first days of September each year. The mudflats and shallows at Middle Creek are providing a suitable alternative for this juvenile bird.Numbers of Lesser Yellowlegs are increasing as flocks drop by for a rest and refueling. Bring your binoculars and your spotting scope to see the oddities that may be hiding among these groups of newly-arriving migrants.
The aquatic environs at Middle Creek attract other species as well. Here are some of the most photogenic…
Wood Ducks atop the dam.The migration of Caspian Terns coincides with that of shorebirds. Just look at that blood-red bill; it’s unmistakable. Two of these big terns are currently patrolling Middle Creek’s lake and shoreline.A female American Kestrel creates a stir among the “peeps” as it passes by. The larger falcons (the Merlin and Peregrine) can be expected to more readily take advantage of concentrations of shorebirds as a food supply.Osprey migration is underway, and many will stop at Middle Creek while in transit.Even if shorebirds aren’t your thing, there are almost always Bald Eagles to be seen at Middle Creek. See you there!
A moderate breeze from the south placed a headwind into the face of migrants trying to wing their way to winter quarters. The urge to reach their destination overwhelmed any inclination a bird or insect may have had to stay put and try again another day.
Blue Jays were joined by increasing numbers of American Robins crossing the river in small groups to continue their migratory voyages. Killdeer (Charadrius vociferous) and a handful of sandpipers headed down the river route. Other migrants today included a Cooper’s Hawk (Astur cooperii), Eastern Bluebirds (Sialia sialis), and a few Common Mergansers (Mergus merganser), House Finches (Haemorhous mexicanus), and Common Grackles (Quiscalus quiscula).
The afternoon belonged to the insects. The warm wind blew scores of Monarchs toward the north as they persistently flapped on a southwest heading. Many may have actually lost ground today. Painted Lady (Vanessa cardui) and Cloudless Sulphur butterflies were observed battling their way south as well. All three of the common migrating dragonflies were seen: Common Green Darner (Anax junius), Wandering Glider (Pantala flavescens), and Black Saddlebags (Tramea lacerata).
The warm weather and summer breeze are expected to continue as the rain and wind from Hurricane Nate, today striking coastal Alabama and Mississippi, progresses toward the Susquehanna River watershed during the coming forty-eight hours.
This Great Blue Heron was joined by numerous other fishermen and a good number of sightseers in the falls today.A colorful young Northern Water Snake (Nerodia sipedon) takes advantage of the sun-heated surface of a Pothole Rock to remain nimble and active. Cooler weather will soon compel this and other reptiles to find shelter for winter hibernation.CLICK ON THE LOGO FOR TODAY’S MIGRATION COUNT TOTALS
A few nocturnal migrants flew through the moonlit night to arrive at Conewago Falls for a sunrise showing this morning. A dozen warblers were in the treetops and a Wood Thrush (Hylocichla mustelina) chattered away in the understory of the Riparian Woodlands. Three species of shorebirds were in the falls and on the Pothole Rocks: Least Sandpiper (Calidris minutilla), Lesser Yellowlegs (Tringa flavipes), and Greater Yellowlegs (Tringa melanoleuca).
A Greater Yellowlegs (right) and two Lesser Yellowlegs sandpipers dropped by for breakfast.
The diurnal migration was highlighted by a Merlin (Falco columbarius), an Osprey, and a Bald Eagle, each flying down the river. Most of the other birds in the falls seemed content to linger and feed. There’s no need to hurry folks, only trouble lurks down there in paradise at the moment.
A light to moderate flight of nocturnal migrants in the eastern United States is displayed on NOAA National Weather Service NEXRAD radar at 4:58 AM EDT. The eye of Hurricane Irma can be seen approaching the Florida Keys. (NOAA/National Weather Service image)CLICK ON THE LOGO FOR TODAY’S MIGRATION COUNT TOTALS
