What is a Merganser?

One of the sweetest subsections of the duck family has to be the sawbills, formally known as mergansers. Mergansers are a family of diving waterfowl in Merginae, the seaduck subfamily of Anatidae. Ironically, only one of these seaducks is truly a seafarer, the others favoring rivers and lakes. The name ‘merganser’ is said to have originated with the German naturalist, Gesner in the mid-16th century. This comes from a combination of the Latin words mergus (diver) and anser (goose).

Mergansers are sometimes referred to sawbills because of their long, serrated bills. These narrow bills, hooked at the tip and set with numerous horny denticulations, are adapted for catching fish, a merganser’s primary source of food. Mergansers primarily feed on small or medium-sized fishes which they capture underwater by swift pursuit. These divers also supplement their piscine diet with frogs and aquatic insects.

Notice the sawbill?
Common Merganser female by John Borg

There are six living species of mergansers, three of which are commonly spotted in North America:

The Common Merganser (Mergus merganser) ranges widely throughout the northern hemisphere. The name “Common Merganser” has always seemed like something of a misnomer since it isn’t particularly common during most of the year (although every winter I find huge flocks outside my office building!) Goosander, which is what this species is called in Europe, may be a more accurate alternative, although Mergus merganser doesn’t really resemble a goose either. The drakes are quite striking, snowy white along its flanks, breast, and tail with head and neck covered in green plumage of such surpassing depth that it appears black.

Common Merganser male by John Borg

Red-breasted Merganser (Mergus serrator) is the marine merganser. It is also a bold world traveler, plying icy waters where usually only scoters and eiders dare to tread. While all mergansers are swift fliers, the red-breast holds the avian record for fastest level-flight at 100 mph (that’s 161 km/h!)

Red-breasted Merganser by Corey Finger

When is a merganser not a merganser? Perhaps when it doesn’t fall in the genus Mergus. However, the Hooded Merganser (Lophodytes cucullatus) is so handsome, the drake flaunting a white, fan-shaped, black-bordered crest, a black body with chestnut flanks, and white breast with vivid vertical black stripes, that any family of fish ducks would be pleased to claim it. Anyway, the hoodie is the only merganser endemic to North America.

Male and female Hooded Mergansers by Corey Finger

The Smew (Mergellus albellus) also falls outside the genus Mergus, so far in fact that it has been known to interbreed with Common Goldeneye (Bucephala clangula). This atypical merganser, which favors the coniferous reaches of Eurasia, is the smallest of all sawbills.

The Chinese Merganser (Mergus squamatus) is also known as the Scaly-sided Merganser, with good reason; this dashing duck resembles a goosander with a wispy topknot and fish scales along its flanks. While this merganser does maintain a strong presence in China throughout the year, it may breed as far north as Russia and winter as far south as Thailand. It is also a species in rapid decline, considered vulnerable by some authorities and endangered by others. Chinese Mergansers do not exhibit the gregarious nature common in most ducks, usually appearing in solitary pairs or very small flocks.

The most threatened of all mergansers is the Brazilian Merganser (Mergus octosetaceus). The sole sawbill of the Southern Hemisphere is down to 200-250 birds extant mainly because the habitat it requires is equally threatened. With hope, this bird will not go the way of its extinct cousin, the Auckland Islands Merganser (Mergus australis). The Brazilian Merganser is rather drab by merganser standards but it does possess truly vibrant vermilion legs.

Richard Crossley has seen a few Hooded Mergansers in his day…