Common Merganser, Mergus merganser

Winter brings a certain serenity to the avian presence on the river. The swallows and swifts no longer dart across the sky, the tall wading birds no longer stalk their prey in the shallows, and the morning chorus of warblers, thrushes, and finches has long since fallen silent. But other pleasures await the birdwatcher who braves the cold for a winter visit to the Connecticut. On the river, winter is the season for waterfowl. Each fall, a multitude of ducks and geese travel down-river from their northern breeding grounds. Although most of them linger only briefly in Massachusetts en route to wintering grounds farther south, some species do spend the winter months in our valley. Among these, the most familiar to the cold-weather observer of the river is the Common Merganser, Mergus merganser. This duck is common and quite conspicuous, owing to the male’s bright white breast and sides, which contrast starkly with his dark green, almost black head.

Common Mergansers are usually seen patrolling the river’s surface in small groups. Periodically, one member of the group disappears beneath the surface, only to emerge a few moments later in a different spot. What’s behind these sudden disappearances? Food. Mergansers are diving ducks, and they eat mostly fish. If a merganser spots a fish while swimming on the surface, it will quickly dive and attempt to grasp its prey with its specially adapted, serrated bill.

If disturbed during its fishing, a merganser will take flight. Takeoff is a rather protracted affair in which the bird skitters along the surface as it labors to get aloft. This long run-up to take-off is required because the merganser’s wings are small relative to its body size. Once the bird is airborne, however, these small wings beat rapidly and effectively, and the Common Merganser is an exceptionally rapid flyer.

Most of our wintering Common Mergansers depart to the north before the breeding season, though a handful of individuals do remain behind to breed in Massachusetts. Most individuals breed in the Canada and the immediately adjacent portions of the U. S. Mergansers are hole-nesters, and usually place their nests in tree cavities. The nest is built from twigs, roots and leaves and lined with feathers and down. A clutch of 9 or 10 eggs is typical, but a clutch can grow larger when other females surreptitiously ‘dump’ extra eggs into a clutch. The unwitting host of this intraspecific parasitism will incubate the dumped eggs as if they were her own. Meanwhile, the father is nowhere to be found, having departed as soon as the last egg was laid.

The female incubates the eggs for about five weeks, eating very little during this period. Fortunately for her, the young are able to leave the nest within a day or two of hatching. They do, however, remain dependent on their mother for some time to come, and can sometimes be seen riding on her back. By the end of the summer, the first-year birds are full grown and fat, ready to begin their first journey to places like our own valley, where they will swim beneath the bare maple trees that overhang the river, and delight any naturalist who chooses to explore the winter river.