Before Hooded Mergansers seek out their nesting cavities in snags and stumps they engage in extensive courtship displays. Males tend to outdo females when it comes to these displays. As the accompanying photograph illustrates, courtship occurs in small groups consisting of at least one female and several males. Males engage in many more types of displays than females. The extent of female courtship consists mainly of head-bobbing and head-pumping. Male displays include crest-raising, head-throws with turn-the-back-of-the-head, head-pumping, head-shaking, upward-stretch, upward-stretch with wing-flap and ritualized (repeated) drinking.
Head-throws (see male in foreground of photo) are the most elaborate display. With crest raised, males bring their head abruptly backward touching their back. A rolling frog-like crraaa-crrrooooo call is given as the head is returned to the upright position and turned away from the intended female. This call sounds so much like a frog that the first time I observed courting Hooded Mergansers I thought it was pure coincidence that I was watching male mergansers display while Leopard Frogs were simultaneously giving their snore-like call. In actuality, the displays as well as the vocal accompaniment were being produced by the mergansers. (Note that one female Hooded Merganser appears not to be all that impressed.)
Hooded mergansers are present in most of the Northeast year round where there is open water, but many move south and southwest in winter. Some actually migrate north to spend winters in the Great Lakes and southern Canada. Their numbers swell in March and April, when migrants are passing through as well as returning. Often within days of when the ice goes out, this smallest (and arguably the most beautiful) of the three North American merganser species appears.
The courtship ritual of hooded mergansers takes place in groups of one or more females and several males. The males raise their crests, expanding the white patch, and engage in behavior known as head-throwing. They jerk their heads backwards until it touches their backs, while giving a frog-like croak. Females court by bobbing their heads and giving a hoarse quack.
Female breeding hooded mergansers select suitable cavities in both live and dead trees in which to nest. Stumps and snags near or in forested wetlands are their preferred nesting sites. Nest boxes are also used by this species, with those over or near water being the most sought after. After a month or a little more, the eggs hatch and downy, day-old chicks jump to the water (or ground) below, in response to their mother’s vocal urging.
Hooded Merganser ducklings typically leap from their cavity nests in trees within twenty-four hours of hatching. Long claws on their feet aid them in climbing up to the opening of the cavity in order to join their mother who is calling from below. The ducklings feed themselves (aquatic insects and invertebrates) from day one, and are capable of shallow dives as soon as they leave their nest. The mother (who has been their sole caretaker since she started incubating the eggs) often moves her brood downstream to larger lakes, rivers and bays from smaller streams and ponds near the nest site. Eventually she leaves her young, anywhere from a month or two after they hatch, often before they can fly.
In northern New England you are most likely to see Hooded Mergansers in the spring and fall when they are migrating to and from their breeding grounds in northern Canada (some nest in New England, as well). Hooded Mergansers tend to arrive in their breeding areas as soon as the ice starts to melt, and have been known to start laying eggs in March in Massachusetts and April in Vermont. Often some of the earliest eggs laid in a nest will freeze and crack and never hatch.
Hooded Mergansers are cavity nesters, frequently choosing trees that are close to ponds, marshes, swamps or streams. They compete with Wood Ducks for nest boxes put out by humans, and females of both species may lay eggs in the same nest, with one or the other incubating the eggs. Sometimes the duck that initiated the nest does the incubation, but more often the hen laying the majority of the eggs will do so. Because both species have the same incubation period, all the eggs hatch at the same time.
Hooded Mergansers are short-distance migrants that can be found in eastern North America year round where ponds and rivers remain open and slow-moving fish, insects and crayfish are plentiful. Some individuals migrate south and southwest in winter — 80% of birds banded in Maine, Vermont, New Hampshire and New York were recovered in coastal Atlantic states from New Jersey to Florida. A smaller number actually migrate north to spend winters in the Great Lakes and southern Canada. While numbers swell in March/April and November in northern New England due to migration, if there is open water you may well see Hooded Mergansers this far north throughout the winter.
Within 24 hours of hatching, Hooded Merganser ducklings leap anywhere from 8 -90 feet from their arboreal cavity nest down to their mother, who is calling to them from the water below. Capable of swimming and diving right away, the ducklings begin feeding themselves immediately. Weighing little more than an ounce, they mostly eat insects, including backswimmers, water boatmen and diving beetles. Eventually, as the ducklings grow, they work their way up to fish and crustaceans — particularly crayfish, such as the pictured merganser has caught. In addition to its size, the lack of a real “hood” indicates that this Hooded Merganser is a youngster.
Although most of New England has Hooded Mergansers year round, we see them most frequently in the spring and fall, when Canadian-nesting individuals are migrating north. They stop to re-fuel in wetlands where they are well adapted for capturing and eating fish, insects and crayfish. The nature of the changes their eye lenses can make, coupled with the high degree of transparency of the membrane that covers their eyes under water give them superior vision under water. Their success in holding onto the struggling prey they capture is greatly increased by the serrated edges of their slender bill. (Photo: female Hooded Merganser)