Mergansers’ “Toothed” Bills
Hooded and Common Mergansers can be found year-round in most of the Northeast. The bills of these cold-hardy, fish-eating ducks are distinctive in that they may be four times as long as wide. In addition, their structure differs from the bills of other ducks in that most ducks have plates (lamellae) or ridges on the cutting edges of their bills that let water escape from the bill when they bring prey to the surface of the water. In mergansers, these plates have been modified to look like saw blades – they aren’t true teeth (birds lack teeth), but are very toothlike – perfect for capturing slippery fish. (Photo: juvenile Common Mergansers)
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Common Mergansers Migrating
Common Mergansers are hardy, fish-eating, cavity-nesting ducks that can be found in New England year round, as they winter as far north as open water allows. However, the birds we see in the winter on large bodies of water most likely are not the same birds that breed here. All North American populations of Common Mergansers migrate, generally short to intermediate distances. Populations near the coast move only short distances, while more interior birds migrate farther. Heavier birds and adult males seem to tolerate colder winter temperatures and remain farther north than immature birds. They can often be seen on large lakes and rivers, as well as the coast, where they form small groups that may gather into large numbers at favored sites.
Migrating Common Mergansers tend to leave late in the fall (this week marks the peak of their fall migration), making them often the last waterfowl migrants to head south. Common Mergansers typically migrate over land at night, and along seacoasts or major river systems by day. In the spring, adult males return north first as soon as open water is available, followed by females a few weeks later. (Photo: 2 juvenile Common Mergansers) Thanks to canoe-steadying Sadie Richards for making it possible for me to take this photograph.
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Common Mergansers Taking Flight
Most ducks can take off nearly vertically from either water or land. However, when taking off from a body of water, unless alarmed, Common Mergansers usually patter along the surface for several yards before taking flight. One would imagine that their flight might not be any more graceful than their take-offs, but the opposite is said to be true of females looking for potential nesting sites. They have been observed maneuvering easily among tree branches seeking a suitable tree cavity in which to lay and incubate their eggs, and once they have found a nest site, they appear to enter and leave their nest holes with ease.
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Peak Migration of Common Mergansers
Common mergansers can be seen year round in northern New England, but in the spring their numbers peak around the first week in April, due to the large number of birds that wintered further south and are migrating to Canadian nesting grounds. These birds are fish eaters, known to consume at least 50 species which they easily grasp with their bill due to the sharp projections along its edges. Egg-laying is still a couple of months away, but coveted tree cavities where they nest are being scoped out. (female common merganser on left, male on right)
Immature Common Merganser Diet
Common Mergansers are primarily fish-eating ducks. Young mergansers require over half a pound of food per day during their first summer, and often supplement their fish diet with insects, mollusks, crustaceans, worms, frogs, small mammals, birds and plants. The pictured immature Common Merganser had just downed a crayfish when it spotted a frog which it succeeded in catching and eventually swallowing.
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