Heavy rains and snow melt have turned the main stem of the Susquehanna and its larger tributaries into a muddy torrent. For fish-eating (piscivorous) ducks, the poor visibility in fast-flowing turbid waters forces them to seek better places to dive for food. With man-made lakes and ponds throughout most of the region still ice-free, waterfowl are taking to these sources of open water until the rivers and streams recede and clear.
The Common Merganser is a species of diving duck with a primary winter range that, along the Atlantic Coast, reaches its southern extreme in the lower Susquehanna and Potomac watersheds. Recently, many have left the main stem of the muddy rivers to congregate on waters with better visibility at some of the area’s larger man-made lakes.Common Mergansers dive to locate and capture prey, primarily small fish. During this century, their numbers have declined along the southern edge of their winter range, possibly due to birds remaining to the north on open water, particularly on the Great Lakes. In the lower Susquehanna valley, some of these cavity-nesting ducks can now be found year-round in areas where heavy timber again provides breeding sites in riparian forests. After nesting, females lead their young to wander widely along our many miles of larger rivers and streams to feed.The behavior of these mergansers demonstrates the stiff competition for food that can result when predators are forced away from ideal habitat and become compressed into less favorable space. On the river, piscivores can feed on the widespread abundance of small fish including different species of minnows, shiners, darters, and more. In man-made lakes stocked for recreational anglers with sunfish, bass, and other predators (many of them non-native), small forage species are usually nonexistent. As a result, fish-eating birds can catch larger fish, but are successful far less often. Seen here are several mergansers resorting to intimidation in an effort to steal a young bass away from the male bird that just surfaced with it. While being charged by the aggressors, he must quickly swallow his oversize catch or risk losing it.
With a hard freeze on the way, the fight for life will get even more desperate in the coming weeks. Lakes will ice over and the struggle for food will intensify. Fortunately for mergansers and other piscivorous waterfowl, high water on the Susquehanna is expected to recede and clarify, allowing them to return to their traditional environs. Those with the most suitable skills and adaptations to survive until spring will have a chance to breed and pass their vigor on to a new generation of these amazing birds.
