Some comparative attributes of unspoiled lotic vs. lentic freshwater ecosystems. Low-gradient (slow-moving) lotic waters often create, and remain connected to, accompanying riverine wetlands (a lentic freshwater ecosystem). These swamps, marshes, and ditches absorb, purify, and infiltrate flood waters while supporting a diverse number of plant and animal species.
We frequently perceive all waterfowl migration to be synchronized with the conspicuous movements of familiar species like Snow Geese, Tundra Swans, and Canada Geese—big flights coming south in October and November, then a return to the north in late February and March. And we’re all quite aware of the occurrence of large gatherings of some of these migrants while they make stopovers on some of our largest lentic (still) waters—the man-made lakes and reservoirs created by damming local streams. But did you know that there are populations of colorful waterfowl with dynamic migrations that extend throughout the winter and early spring with movements that are often continuous. Under favorable conditions, these birds favor the lotic (flowing) waters of the river and its larger tributaries as they transit the lower Susquehanna valley. That’s because unpolluted lotic freshwater ecosystems support a greater diversity of plants and animals than lentic waters, and therefore offer more opportunities for hungry migrating waterfowl to find food. Let’s have a look at some of the species that visit the river during their seasonal journeys…
While the urge to head south in the autumn is largely stimulated by the shortening of the photoperiod, it is the presence of ice, particularly on glacial lakes throughout the lands to the north of the lower Susquehanna River basin, that pushes many diving ducks to finally make their way south toward the guarantee of open-water feeding areas along the coast. This movement may occur at anytime between November and late February or, as we have seen during some of the mild winters of recent decades, it may scarcely be noticed at all.Common Mergansers often lead they way when it comes to migratory diving ducks. They regularly move south in conspicuous numbers by late November and December and are regularly pushing north as soon as the ice begins to melt. During a typical year, it is not unusual for some populations of these large diving birds to remain north of us during the winter. Then, in the days after a sudden rush of frigid polar air, an appreciable increase in ice cover will force a mid-winter movement of birds down the Susquehanna.Temperatures in lotic fresh waters vary over the length of the stream or river. They are largely determined by the collective impact of the numerous sources of heat flux depicted in this graphic. (Environmental Protection Agency image)Buffleheads begin passing through the lower Susquehanna region in Novemeber on their way to coastal saltwater bays for the winter. Lingering populations feed by diving in the river’s pools and riffles for benthic invertebrates including snails and insect larvae. Lesser quantities of aquatic plant matter supplement their diet.Many Common Goldeneyes will remain on shallow, ice-free waters of the northern lakes and rivers sculpted by the most recent glacial event, but only until they are forced south into and through the lower Susquehanna valley by the encroachment of freezing conditions. On the river, they are among the dozen or so species of diving ducks we see visiting or passing through during the typical late fall and early river.
During their visits to the lotic (also known as riverine) fresh waters of the Susquehanna and its largest tributaries, benthic-feeding waterfowl make short dives to take advantage of the plants, small fish, invertebrates, and other food sources inhabiting the stream bottom in the riffles and pools of the free-flowing waterway. Substrates, listed here by size (in descending order), along with other parameters influenced by this zonation determine the variety and abundance of the forage available to migrating waterfowl and other consumers. Ice or high water and poor visibility due to flooding can render the riffles and pools of the channel unusable for feeding. The birds must then choose to either linger and rest without feeding or leave the lotic freshwater habitat to seek sustenance. During a flood, this may require relocation to a nearby lentic (still) body of fresh water such as a lake or reservoir. The presence of ice will almost invariably force the birds to fly on to the Atlantic Coastal Plain and the tidal waters of its bays and estuaries.Hooded Mergansers are one of the few species of diving ducks likely to utilize flooded shoreline timber and riverine (fluvial) wetlands as refuge from high water on Susquehanna.A Pied-billed Grebe and a pair of Canvasbacks on an ice-free stretch of the lower Susquehanna in mid-winter feed and loaf in a riffle-flanked pool where a large mat of American Eelgrass, a submerged aquatic plant also known as Tapegrass or Wild Celery, grows during the summer. The vast mosaic of riffles and pools in a river this size offers tremendous opportunities for a diverse array of aquatic species to find their niche wherein they can survive and flourish.The presence of ice forces Buffleheads and other diving ducks to gather in turbulent open water, often below a riffle or dam. Another alternative is to continue on toward the salty bays and estuaries of the coast. High water may push these birds into the shallows among the flooded woods to feed, but they seldom utilize heavily forested riparian wetlands as a refuge due to their need for a running start to get airborne.
Riffle and Pool Characteristics of High Gradient (A) and Low Gradient (B) Streams. This graphic illustrates the change in deposition characteristics of a stream or river as its gradient decreases. A high-gradient stream (A) has a rapid velocity, often forms falls, and tends to carry away a high volume of all but the largest of particles of potential substrates as they erode from the surrounding landscape. On a low-gradient stream, the loss in water velocity reduces the water column’s ability to transport even the smallest of substrate particles. Deposition of this gravel, sand, silt, and clay forms lateral bars that over time create the familiar meandering path of a naturally flowing lowland stream. (National Park Service image)Benthic substrates in lotic freshwater pools and riffles support an abundance of life forms ranging from colorful diatoms on rocks and cobble, to invertebrates including snails and insect larvae, to fishes like this young Channel Catfish. Free of accumulations of sediment, this river bottom not only provides habitat for a healthy fishery, it facilitates the bidirectional exchange of water between the Susquehanna and its underlying aquifer.On the lower Susquehanna, populations of young Quillback suckers are found almost exclusively in clear, high-gradient pools.The Harlequin Duck winters along the rocky shores and man-made jetties of the Atlantic coast. In summer, they nest on fast-moving, headwater streams well to our north. Very rare on the Susquehanna, this is the first of two individuals found during March and April of 2025. It was observed feeding in the swift waters of the high-gradient riffles and pools where the river cuts through Blue Mountain north of Harrisburg. During previous weeks, Harlequin Ducks were being seen along the coast as far south as the mouth of the Chesapeake at Cape Charles, Virginia. It’s very possible that some of these birds traveled north through the bay area and up the Susquehanna on their way north.
Fluvial Geomorphology of a Stream. Many of the Susquehanna’s tributaries pass through each of these three erosional zones. Along the way, they carry out the process of breaking down the mountains formed by the Allegheny orogeny, the collision of North America and Africa that created the supercontinent Pangea about 325 to 260 million years ago (during portions of both the Carboniferous and Permian periods). Today’s main stem of the lower Susquehanna passes through a transfer zone (Zone 2), carrying eroded materials to a depositional zone (Zone 3) located within the ancient Susquehanna canyon stretching from Havre de Grace, Maryland, to Norfolk Canyon on the edge of the continental shelf. Within this zone, more than a 10,000-year accumulation of post-glacial sediments lies submerged by the rising waters of the Atlantic Ocean and Chesapeake Bay. Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path has eroded passage through the highlands. (National Park Service image)Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path continues to erode passage through the bedrock. On this 1908 map of the Susquehanna at Conewago Falls, alluvial terraces of gravel, sand, silt, and clay can readily been seen as pale areas nearly lacking brown contour lines along the shorelines and islands of the river. Deposits within most of these terraces date back to the melt period following the most recent glacial event and beyond. The delta shown at the mouth of Conewago Creek (west) includes massive volumes of material deposited by both the creek and the river. This delta is currently known as Brunner Island, much of it developed as the site of a coal/gas-fired electric generating station. Terrace deposits along the Susquehanna’s shorelines created extensive perched marshes and swamps (wooded marshes) fed by rains, high river water, small streams, and springs, the latter often seeping from the base of the rocky escarpments carved by the ancient Susquehanna and defining the present-day inland border of the floodplain. We call these sites “Alluvial Terrace Wetlands”. Few of these critical components of river morphology survive. Those not drained for farmland were obliterated by urbanization and canal, railroad, and highway construction. (United States Geological Survey base image: Middletown, PA, quadrangle, 1908)Water Willow is a familiar emergent plant that colonizes lateral bars and other alluvial deposits in low-gradient segments of the Susquehanna.The fine roots of Water Willow collect sediment and absorb nutrients while creating dense cover for young fish and numerous species of invertebrates including the Virginian River Horn Snails seen here.
Prior to the nineteenth century, the low-gradient flow regime of the river both above and below the riffles at Chiques Rock (lower right on map) created prime wildlife habitat. The natural accumulations of nutrients and substrates carried into and through the lotic waterway’s pools and riffles were cycled into an ideal growing medium for extensive mats of American Eelgrass and other aquatic plants. This underwater forest hosted a seemingly endless abundance of invertebrates and fishes (both resident and migratory)—supporting a variety of consumer species including various populations of humans. But soon after the mass clearing of much of the watershed’s land for farming and lumber, the mill ponds created by dams constructed on streams to power saw and grain mills became brimful with sediments eroded from the unprotected ground. During storm events, torrents of these sediments then flowed full bore toward the Susquehanna, and began accumulating in the low-gradient segments of the river.
Sediments left behind after the removal of mill dams are known as legacy sediments. They disconnect the stream from its historic floodplain and riverine (fluvial) wetlands, thus intensifying the impact of high water in the surrounding landscape. As these nutrient-charged deposits wash away, they become a source of pollution in the waters of the Susquehanna and Chesapeake.A mat of American Eelgrass growing in the flowing waters of the Susquehanna below Conewago Falls. Eelgrass and other submerged aquatic plants provide essential habitat for a wide variety of small fish and invertebrates while also consuming nutrients deposited in the cobble, gravel, and sand substrate of the river’s pools. Excess quantities of smaller particles of silt and clay can clog the substrate and thus inhibit the hyporheic exchange of water between the stream channel and the underlying aquifer, often diminishing the biomass and diversity of organisms inhabiting this benthic habitat. Buried in these life-choking sediments, the river bottom becomes inhospitable to growth of submerged aquatics including eelgrass.This low-gradient stretch of the Susquehanna at Marietta flows parallel to the Chickies Quartzite “Hellam Hills” before making a sharp right turn to punch through the ridge as a series of rapids at Chiques Rock. Formerly a fully functional lotic ecosystem and a paradise for migrating waterfowl, this river segment is now impaired by accumulations of nutrient-laden sediments from agricultural and urban runoff.Nutrient and sediment-loaded flood waters roar across the diabase boulders at the York Haven Dam and Conewago Falls, a high-gradient segment of the Susquehanna.They continue past Brunner Island (left power plant stacks) and through Haldeman Riffles and the Shocks Mills Railroad Bridge……into the stretch of river known as the “Marietta broads” along the base of the Chickies Quartzite “Hellam Hills”. The low stream gradient here produces a slower current and increased deposition of sediments.As the flood surges through the riffle and pool complex at Chiques Rock, the high stream gradient maintains a velocity in the water column sufficient to keep additional sediments in suspension until they reach the low-gradient river segment just downstream at Washington Boro, site of a naturally occurring lateral bar area known as the Conejohela Flats. These bars now lie within the man-made depositional zone known as “Lake Clarke”. Created nearly a century ago by construction of the Safe Harbor Dam, this impoundment is accumulating astounding volumes of nutrient-loaded sediments that continue to encapsulate the flats within a stream-impairing delta.Anytime from November to April on the lower Susquehanna, a group of Redheads, Canvasbacks (3 birds to right of the middle of the picture), and a Horned Grebe (lower left) is a welcome sight in a riverine pool known to have a summertime growth of American Eelgrass. Noted Dr. Herbert Beck in 1924 when describing the Canvasback, “Like all ducks, …, it stops to feed within the county (Lancaster) less frequently than formerly, principally because the vast beds of wild celery which existed earlier on broads of the Susquehanna, as at Marietta and Washington Borough, have now been almost entirely wiped out by sedimentation of culm. Prior to 1875 the four or five square miles of quiet water off Marietta were often as abundantly spread with wild fowl as the Susquehanna Flats are now. Sometimes there were as many as 500,000 ducks of various kinds on the Marietta broad at one time.”Today, seeing just dozens of Aythya genus ducks (Redheads, Canvasbacks, scaup) on the lower Susquehanna is a notable event. If they happen to be forced down by inclement weather while migrating through, you might get lucky enough to see several hundred.While the recovery of eelgrass/wild celery beds on the Susquehanna is trivial in scale and offers little support for numbers of waterfowl to return to historic levels, restorations on the upper Chesapeake in the vicinity of the Susquehanna Flats between Havre de Grace and Aberdeen Proving Grounds may have helped refuel a gathering of mostly Aythya genus ducks during the final days of February. This mass of ducks, many of which were forced south from the frozen Great Lakes during the previous weeks (some by way of the ice-choked Susquehanna) were apparently making an abrupt turn to make their way back north. Their stay was brief, but estimates by local birders put their numbers as high as one half million. The vast majority of the concentration consisted of Aythya species: Redheads, Canvasbacks, Ring-necked Ducks, and both Lesser and Greater Scaup. It probably included a mix of birds including both northbound migrants from further down the coast and the aforementioned refugees that had just arrived to pay a quick visit while escaping the late-season ice before turning around.During the past two centuries, as food supplies in the Susquehanna grew increasingly compromised for benthic feeders like these Lesser Scaup and other diving ducks, a change in distribution was necessary for survival.As individual species, Lesser Scaup and other waterfowl that fail to adapt to natural or man-made changes in their habitats and food supplies may see their overall global numbers falter.
Despite being located in the transfer zone, the lower Susquehanna has become a significant depositional zone along much of its length, mostly courtesy of the placement of sediment-trapping man-made dams.
Following construction of the mill dams and ponds on nearly every mile of the lower Susquehanna’s low-gradient tributary streams, enterprising parties moved on to the river. The first significant spans were constructed using wide timber cribs filled with large rock. They were placed to create water deep enough to allow canal boats to cross the Susquehanna at both Clark’s Ferry at the mouth of the Juniata River in Dauphin County and at Columbia/Wrightsville. These dams also diverted water into the newly excavated canals—the Pennsylvania Eastern Division Canal (completed in 1833) which followed the river’s east shore from Clark’s Ferry to Columbia, and the Susquehanna and Tidewater Canal (completed in 1840) along the west shore from Wrightsville to Havre de Grace, Maryland. Placement of these sediment-trapping man-made dams began a process of converting vast mileage of the lower Susquehanna from a transfer zone into a deposition zone. In addition, layout of the canals and locks followed the contours along the base of the riverside ridges, seriously altering most of the alluvial terrace wetlands that the river had created as a feature of its floodplain during the post-glacial period.
Construction of the canal dams was just the beginning. During the twentieth century, more massive dams would be added to the main stem of the river for hydroelectric energy production at York Haven, Safe Harbor, Holtwood, and Conowingo. Upon their completion, the days of unassisted anadromous fish migrations were over. On both the river and its tributaries, smaller dams including dangerous low-head dams maintain water levels for boating and recreation. They too create current-diminishing, pseudo-lentic waters that blanket the lotic riffle and pool substrates with polluted sediments.
MAN-MADE DAMS TURN LOTIC WATERS INTO UNFLUSHED TOILETS
The construction of dams on the lower Susquehanna has converted vast mileage of the river from a lotic freshwater system into a series of man-made lentic freshwater lakes. These areas have lost their function as a lotic transfer zone and are now a sort of dysfunctional series of depositional zones collecting vast volumes of sediment containing nutrients and other pollutants. Within each impoundment, the reduced velocity of the river causes it to drop suspended sand first, then the finer particles of silt and clay closer to the dam. The flow regime of riffles and pools is lost and the hyporheic zone that exchanges water between the river and the underlying aquifer is clogged. These impaired segments of river become ripe for eutrophication: algal blooms followed by die offs that can lead to a fatal reduction of dissolved oxygen in the water column.Deposits of lateral bars of sediment in low-gradient segments of the Susquehanna can create shallow water feeding habitat for puddle/dabbling ducks like these Gadwall. Where sediment pollution is severe, benthic foods in these areas often consist mostly of invertebrates and plant matter deposited by the current, the buried substrates devoid of a functioning ecosystem and the waters subject to eutrophication.Common Goldeneyes on a patch of open water on an otherwise ice-covered “Lake Clarke”, the impoundment created by Safe Harbor Dam. While they may find this spot advantageous for loafing, the food supply over the sediment-buried substrate will be limited.By the end of the twentieth century, accumulations of polluted sediments behind lower Susquehanna dams were nearing capacity. There is no working plan to attenuate the massive release of these pollutants that may be triggered by a catastrophic flood. The effort to reduce nutrient and sediment runoff remains the focus so that new loading is kept to a minimum and won’t add to the capacity problems at the dams or continue downriver to the Chesapeake at full strength when the dams are full. Alleviating the sediment aggregation problem within the river’s impoundments is a tall order and a dilemma not easily solved. (United States Geological Survey image)Common Mergansers will feed where benthic substrate supports the small fish and invertebrates they prefer. They will, however, gather in extraordinary numbers on the “lakes” created by riverine dams. Though they can only feed on what floats in with the current, hundreds or sometimes thousands of Common Mergansers will concentrate on “Conowingo Pond” during the late fall or early winter. There, safety in numbers gives them some guarantee of protection against the multitudes of eagles that simultaneously frequent the vicinity. Another advantage of staging on “Conowingo Pond” is its close proximity to favorable feeding areas on upper Chesapeake Bay and stretches of the Susquehanna where lotic riffles and pools offer abundant opportunities below the river’s dams.Fortunately for everything else living in the benthos, Common Mergansers are big enough to devour invasive, non-native Rusty Crayfish when they find them in our lotic waterways.
TIME TO CLEAN UP OUR ACT
WHERE DOES YOUR STORMWATER GO?
Channelized Urban/Suburban Streams Function as Sewers. They have no attached lowlands or floodplains to absorb, purify, and infiltrate runoff from rain events. Pollutants including litter, pet waste, lawn chemicals, tire-wear particles, hazardous fluids, and sometimes untreated human excrement flush unchecked from the municipal storm drainage system into the waterway. Thermal shock from summer downpours washing across sun-heated pavements can kill temperature sensitive fishes and other aquatic life. Nutrient and sediment loads from these impaired tributaries later accumulate downstream in low-gradient segments of the Susquehanna, turning the river into an open-air cesspool. Aggressively working to implement projects that eliminate these sources of pollution are the only effective way to keep the problem from getting worse. Making things better requires a lot more dedication and effort. (United States Geological Survey image by Frank Ippolito)
RIPARIAN BUFFERS MAKE A DIFFERENCE…WIDER IS BETTER
To sequester sediment and cycle nutrients (primarily nitrogen and phosphorus) contained in farm runoff, the U.S.D.A. recommends installing riparian buffers between streams and lands used for grazing and raising crops. To protect pollinating species including bees and butterflies from pesticide drift and eroding soils rich in fertilizers, they further recommend installing a stand of wind-pollinating plants such as conifers, oaks, and birches between the field and streamside plantings. These same conservation practices improve water quality and wildlife habitat on waterways located in residential and commercial areas as well. (United States Department of Agriculture image, click to enlarge)
FLOODPLAIN RESTORATION
Regardless OF HOW LONG YOU’VE BEEN CONDITIONED TO THINK OTHERWISE, THIS IS A DYSFUNCTIONAL, POLLUTED CREEK—AND IT NEEDS HELP
A channelized low-gradient stream eroding a path through deposits of legacy sediments displaces flood waters into previously unaffected areas and provides a continuing source of nutrient and sediment pollution during storm events. These impaired waters have a diminished capacity for supporting aquatic life including fishes.
RESTORED TO ITS HISTORIC FUNCTIONS
On an adjacent segment of the same creek, this legacy sediment removal project restored a braided meandering channel and connected it to its newly liberated, historic floodplain. In just their second year, the fluvial wetlands are effectively absorbing stormwater and sequestering nutrients as an attached component of the stream’s riffle and pool complex. During our visit earlier this week, we found American Toads, Northern Leopard Frogs (Lithobates pipiens), and Northern Spring Peepers breeding here. It’s just as Castor canadensis would have it!
“STOP HEMMING AND HAWING AROUND ALREADY”
“HEY COWBOY, HOW ‘BOUT GETTIN’ THEM FILTHY LITTLE DOGIES OUTTA DAT CRICK?”
Here’s a polluted stream in a pasture with grazing livestock. The site is a former mill pond within which the creek eroded a channel following removal of the dam. The animals defecate and urinate where access to water is gained at a broken down embankment of the nutrient-loaded legacy sediments deposited in the pond more than a century ago. It’s a haphazard form of animal husbandry and a reminder that all it takes is just one stubborn jackass to foul up the whole waterway.
DIRECT SOURCES OF NITROGEN (AMMONIA) POLLUTION IN STREAMS
DID YOU KNOW that a dairy cow produces about 80 pounds of waste (excrement and urine) every day?
DID YOU KNOW that a horse produces about 50 pounds of waste (excrement and urine) every day?
DID YOU KNOW that a human produces about 3 to 4 pounds of waste (excrement and urine) every day? The exceptions, of course, are those who continue to insist that raising farm animals in and alongside a body of water is okey-doke—a harmless practice. These individuals tend to retain the former constituent of human waste and are thus full of it.
“ATTABOY TEX, THAT’S MORE LIKE IT!”
Now that’s better. Legacy sediments have been removed to reconnect the stream to its floodplain. A livestock crossing and exclusion fencing has been installed, and a nutrient-consuming riparian buffer has been planted. This creek segment’s pollution woes have been mitigated. Do you have a neighbor needing this type of remedial work on their farm? Have them call your local conservation district office for advice. Some programs include financial assistance covering the costs of installation as well as monetary incentives for helping to clean up the water.
AND FINALLY
WHEN IT COMES TO BUILDING DAMS ON LOTIC FRESH WATERS…
…LEAVE IT TO THE BEAVERS
North American Beavers (Castor canadensis) create habitats that connect the riffle and pool regime of a low-gradient stream to a surrounding fluvial wetland that retains sediments, cycles nutrients, and provides essential habitat for hundreds of plant and animal species. Floodplains are for flooding. And if a beaver floods an area, you can be guaranteed that it was already part of a floodplain. You see, beavers don’t encroach upon humans, it’s humans doing the encroaching upon beavers. (National Park Service image)
MAD HATTERS
DID YOU KNOW that even before the landscape was cleared for farms and a supply of timber, and before mill dams on local creeks began accumulating soil runoff from the consequently barren hillsides, all the North American Beavers, the keystone species of lower Susquehanna stream ecology, were killed and sold to make hats? It’s no wonder things are fubar!
COMING SOON…
Horned Grebes are regular migrants and sometimes winter residents on ice-free stretches of the lower Susquehanna. They spend their time plying the benthic substrate of the river’s clear riffles and pools for a variety of invertebrates and small fish. Look for them moving north in coming days sporting this beautiful breeding plumage.April and early May are prime time for observing Common Loons on the Susquehanna as they undertake a journey from the Atlantic surf where they spent the winter to nesting sites on northern lakes. For this migrant in breeding plumage, clear water for sighting plenty of benthic life in the river’s riffles and pools assures a successful dive in search of energy-replenishing forage.
In early April of each year, we like to take a dreary-day stroll along the Susquehanna in Harrisburg to see if any waterfowl or seabirds have dropped in for a layover before continuing their journey from wintering waters along the Atlantic seaboard to breeding areas well to our north and northwest. As showers started to subside this Saturday morning past, here are some of the travelers we had the chance to see…
Hundreds of scaup were feeding at mid-river. To remain in suitable foraging habitat, the group is seen here flying upstream to the area of the Governor’s Mansion where they would commence yet another drift downstream to Independence Island before again repositioning to a favorable spot.By far, the majority of the ducks in this flock were Lesser Scaup showing white inner margins of the secondary flight feathers and more grayish margins in the primaries. Several Greater Scaup, including the one denoted by the hairline in this image, could be detected by the presence of bright white margins not only in the secondary flight feathers, but extending through the primaries as well.A pair of Lesser Scaup feeding along the river shoreline at the Governor’s Mansion. Both scaup species spend the colder months in bays and coastal estuaries, but the Lesser Scaup is the most likely to be found venturing inland to fresh water in the southern United States during winter. The Lesser Scaup nests in the northwestern United States and in the southern half of Canada. The Greater Scaup is the more northerly nesting species, spending its summers at the northern edges of the border provinces and beyond.Common Loons spend the winter in Atlantic surf. April is the best time to see them on the lower Susquehanna River as they drop in to rest and reenergize during a break in their annual northbound trip to nesting sites on the lakes and ponds left behind by the retreat of Pleistocene glaciers.We saw dozens of Buffleheads during our morning hike, often segregated into paired couples like this one. Being cavity nesters, these migrating ducks are headed no further north than southern Canada, to lakes and ponds within forests, for the summer.Harlequin Ducks (Histrionicus histrionicus) spend the summer nesting on turbulent high-gradient streams in Canada and Greenland. They mostly winter along rocky coastlines as far south as New England, but have adapted to feeding along man-made rock jetties in coastal New York and New Jersey. This winter, they were seen along jetties and sea walls at least as far south as Cape Charles, Virginia, and the mouth of Chesapeake Bay. During the past month, at least two Harlequin Ducks, including this male seen in flight on Saturday, have appeared on the river in the Harrisburg area, possibly as strays from this year’s wintering population at the mouth of the bay. These ducks are very rare habitat specialists, possibly (according to Behrens and Cox, 2013) numbering less than 1,500 birds along the entire east coast.In spring, the Horned Grebe transitions from a drab gray-brown winter (basic) plumage into rather surprisingly colorful breeding (alternate) plumage.An adult Horned Grebe in breeding (alternate) plumage. Horned Grebes spend the winter on large rivers, bays, and ocean waters from Nova Scotia to Texas. They are presently on their way to breeding areas on ponds and lakes in Alaska and Canada west of Ontario.
If you want a chance to see these seldom-observed visitors to the lower Susquehanna at Pennsylvania’s capital city, try a morning walk along mid-town’s Riverfront Park from Maclay Street to Forster Street. Also, try a stroll on City Island, particularly to the beach at the north end where you have a view of the mid-river areas upstream. To have better afternoon light, try the river’s west shore along Front Street in Wormleysburg from the Market Street Bridge upstream to Conodoguinet Creek. Once there, be certain to check the river from the Pennsylvania Fish and Boat Commission’s West Fairview Access Area at the mouth of the creek. And don’t be afraid to visit on a gloomy day; you never know what you might find!
Don’t forget to check the trees along the river shoreline where early stonefly hatches can often attract hungry insectivores. We found this and six other Eastern Phoebes crowded into the trees at water’s edge just upriver from the Governor’s Mansion during Saturday’s migrant fallout.
SOURCES
Behrens, Ken, and Cameron Cox. 2013. Seawatching: Eastern Waterbirds in Flight. Houghton Mifflin Harcourt Publishing Company. New York, NY.
As anticipated, lakes and ponds throughout the lower Susquehanna basin are beginning to freeze. Fortunately for the waterfowl thereon, particularly diving ducks, the rain-swollen river is slowly receding and water clarity is improving to provide a suitable alternative to life on the man-made impoundments.
The Susquehanna, ice-free and receding from near flood stage levels last week, can presently provide suitable habitat for diving ducks and other wintering waterfowl.A feeding Common Merganser takes a breather between dives on the Susquehanna in Dauphin County, Pennsylvania.
The deep freeze is not only impacting ponds and lakes in the lower Susquehanna valley, but is evidently affecting the larger bodies of water to our north and northwest. During Tuesday’s snow event, thousands of diving ducks arrived on the main stem of the river—apparently forced down by the inclement weather while en route to the Atlantic Coast from the Great Lakes and its connected waterways, which are currently beginning to freeze.
Tuesday’s snowfall not only blanketed the landscape with a coating of white,……it prompted thousands of migrating “bay ducks” including Canvasbacks, Redheads, scaup, and other diving species to seek open water and make a forced landing.Scaup were by far the most numerous of the birds in the grounded flight. The majority appeared to be Lesser Scaup.Scaup in flight on the Susquehanna.A mixed raft of scaup and Buffleheads seen one day after a snowstorm-related fallout of late-season migrants. A single Long-tailed Duck, a species formerly known as Oldsquaw, can be seen to the lower left.Scaup and a Bufflehead (center) fly past a Long-tailed Duck. Because they winter primarily in coastal waters, both of the latter species are sometimes categorized as “sea ducks”.A small flock of Ruddy Ducks.While Common Mergansers on the Susquehanna are fish eaters (piscivores), other diving ducks observed during this fallout event are primarily benthic feeders, eating plant matter and invertebrate animals collected from the river bottom.A small flock of Common Goldeneyes. They, like the Long-tailed Duck and Bufflehead, are sometimes known as a species of “sea duck”.Another mixed raft of scaup and Buffleheads loafing on the Susquehanna.Large numbers of waterfowl attract the attention of the river’s ever-vigilant Bald Eagles.An adult Bald Eagle patrolling the area of a fallout in search of dead, sick, or injured ducks. In addition to the victims of naturally occurring ailments, eagles find birds and mammals wounded or killed by hunters to be particularly attractive sources of food. They can, therefore, quite easily ingest pieces of shot. Because eagles in the lower Susquehanna valley feed as frequently in upland habitats as they do in riverine environs, use of alternatives to toxic lead shot is prudent practice in all habitat types.A Bald Eagle in the first month of its fourth calendar year. Though not yet matured to breeding age, this bird is nevertheless smart enough to be on the lookout for vulnerable or deceased waterfowl during a post-storm fallout.A fallout of some migrating waterfowl seldom escapes notice by members of the gasoline and gunpowder gang……who find their very presence an irresistible temptation to arouse their adolescent urges……to get an adrenaline junkie’s fix.
With more snow on the way for tomorrow, you may be wondering if another fallout like this could be in the works. The only way to find out is to get out there and have a look. Good luck! And be good!
Following the deep freeze of a week ago, temperatures soaring into the fifties and sixties during recent days have brought to mind thoughts of spring. In the pond at susquehannawildlife.net headquarters, Green Frogs are again out and about.
A pair of Green Frogs seen today alongside the headquarters pond. A sign of spring?
But is this really an early spring? Migrating waterfowl indicate otherwise. Having been forced south from the Great Lakes during the bitter cold snap, a variety of our tardy web-footed friends belatedly arrived on the river and on the Susquehanna Flats of upper Chesapeake Bay about ten days ago. Now, rising water from snow melt and this week’s rains have forced many of these ducks onto local lakes and ponds where ice coverage has been all but eliminated by the mild weather. For the most part, these are lingering autumn migrants. Here’s a sample of some of the waterfowl seen during a tour of the area today…
Like other late-season migrants, Snow Geese take advantage of open water on area lakes until ice forces them south to the Atlantic Coastal Plain. In a little more than a month from now, they’ll begin working their way north again.Tundra Swans and American Black Ducks loafing on an ice-free lake.The non-native Mute Swan has become an invasive species. Because they are predominantly non-migratory, groups of Mute Swans congregating in valuable wetland habitat can decimate these aquatic ecosystems with their persistent year-round feeding. Their long necks help them consume enormous quantities of benthic foods that would otherwise be available to migratory diving ducks during their autumn and spring stopovers.Small flocks of Gadwalls will sometimes spend the winter on ice-free vegetated ponds in the lower Susquehanna region.A mixed flock of diving ducks on a small lake. Let’s take a closer look!Six Redheads, three Lesser Scaup (top row left), and a Canvasback (upper right).Redheads.Buffleheads.An adult male Lesser Scaup.A female (right) and a first-winter male (left) Lesser Scaup.Canvasbacks and a Ruddy Duck.
With the worst of winter’s fury still to come, it’s time to say farewell to most of these travelers for a little while. With a little luck, we’ll see them again in March or April.
Our official susquehannawildlife.net prognosticator climbed out of its winter hideout today to have a look around. Then, without hesitation, the forecast for 2023 was issued, “Winter Stinks!”
In late March and early April, a rainy night and fog at daybreak can lead to an ideal morning for spotting migratory waterfowl and seabirds during their layover on the lower Susquehanna. Visibility was just good enough to spot these birds at Harrisburg, Pennsylvania, most of them feeding at midriver.
Northern Shovelers are regular migrants, more often seen on ponds and in wetlands than on the river.A pair of American Wigeons head upriver.A Horned Grebe.A small flock of northbound Buffleheads.Ring-necked Ducks.Lesser Scaup, eight of the more than 100 seen along Front Street in Harrisburg at the Pennsylvania Governor’s Residence. Note how the white bar on the wing’s secondaries becomes diffused and dusky in the primaries.Lesser Scaup spend the winter on bays and lakes to our south.More Scaup, the lead bird with bright white extending through the secondaries into the primaries is possibly a Greater Scaup (Aythya marila).Long-tailed Ducks, formerly known as Oldsquaw, are a diving duck that winters on the Great Lakes and on bays along the Atlantic Coast. They nest on freshwater ponds and lakes in the tundra of Canada and Alaska.A male Common Merganser.This pair of Hooded Mergansers may be nesting in a tree cavity nearby.The local Peregrine Falcon grabbed a passing Common Grackle……prompting the more than 100 Bonaparte’s Gulls in the vicinity to quickly depart and fly upstream.It pays to keep an eye on the trees along the shoreline too. Migrants like this Northern Flicker are beginning to come through in numbers.
You remember the signs of an early spring, don’t you? It was a mild, almost balmy, February. The earliest of the spring migrants such as robins and blackbirds were moving north through the Lower Susquehanna River Watershed. The snow had melted and ice on the river had passed. Everyone was outdoors once again. At last, winter was over and only the warmer months lie ahead…beginning with March.
Common Grackles are often the first perching birds to begin moving north through the lower Susquehanna valley in spring. They often winter in large roving flocks of mixed blackbird species on the nearby Atlantic Coastal Plain Province. These flocks sometimes wander the farmlands of the lower Piedmont Province near the river, but rarely stray north of the 40th parallel before February.
Ah yes, March, the cold windy month of March. We remember February fondly, but this March has startled us out of our vernal daydreams to wrestle with the reality of the season. And if you’re anywhere near the Mid-Atlantic states on this first full day of spring, you know that a long winter’s nap and visions of sugar peas would be time better spent than a stroll outdoors. Presently it’s dusk, and the snow from the 4th “Nor’easter” in a month is a foot deep and still falling.
In honor of “The Spring That Was”, here then is a sampling of some of the migratory waterfowl that have found their way to the Lower Susquehanna River Watershed during March. Some are probably lingering and feeding for a while. All will move along to their breeding grounds within a couple of weeks, regardless of the weather.
Tundra Swans will migrate in a northwest direction to reach breeding grounds west and north of Hudson Bay.Migratory Canada Geese departing the Chesapeake Bay area typically pass over the lower Susquehanna valley at high altitudes. A south wind can bring a sustained day-long flight of migrating geese and ducks over the region on a given day in late-February or March.Snow Geese (Anser caerulescens) historically wintered in the marshes of the Atlantic seaboard where the tide cycle kept vegetation primarily snow-free for feeding. Removal of hedgerows and intensive farming since the 1980s has attracted these birds to inland agricultural lands during their preparation for the move north. For nearly three decades, tens of thousands have annually begun their spring journey with a stopover at the Middle Creek Wildlife Management Area. Flocks range widely from Middle Creek to feed, commonly as far west as the fields of the Conewago Creek valley in the Gettysburg Basin to the east of Conewago Falls. American Black DucksA pair of Northern Shovelers (Anas clypeata).Ring-necked Ducks (Aythya collaris) are “diving ducks”.A male Lesser Scaup, Aythya affinis, (front center) and Ring-necked Ducks (rear and left) seen between feeding dives.A male Bufflehead (Bucephala albeola). These miniature diving ducks will sometimes winter on the Susquehanna in “rafts” of dozens of birds.Tundra Swans journey toward the “Land of the Mid-Night Sun”.
