Mergansers are diving ducks belonging to the family Anatidae. These aquatic birds are highly adapted to hunting underwater, a behavior that distinguishes them from surface-feeding ducks. Their specialized anatomy has earned them the nickname “sawbills.” The name “merganser” comes from the Latin mergus (“diver”) and anser (“goose”), accurately describing this large, diving waterfowl. Mergansers are found across the Northern Hemisphere in various freshwater and coastal environments.
Defining Physical Traits: The Sawbill Bill
The defining characteristic of mergansers is their bill, which differs significantly from the broad, flattened bill of most other ducks. Mergansers possess a long, thin, narrow bill that tapers toward the tip, designed for catching fish. This bill is equipped with numerous backward-pointing, tooth-like serrations along the edges of both mandibles.
These sharp projections function like the teeth of a saw, giving rise to the common name, “sawbill.” The serrations provide an exceptional grip, preventing slippery fish from escaping once captured underwater. The bill often features a small hook at the tip, further aiding in the secure capture of prey.
Mergansers are streamlined birds with a long body shape, allowing for efficient movement during dives. Their legs are positioned far back on the body, a common trait in diving ducks, which provides powerful propulsion for swimming underwater. Most species also feature a crest of feathers on the back of the head, which can appear shaggy or fan-shaped.
The Three Main North American Species
Three species of mergansers are regularly found across North America, distinguishable by size, plumage, and crest shape. The Common Merganser (Mergus merganser) is the largest of these species. The male has an iridescent dark green head, a black back, and a gleaming white body that often shows a subtle salmon-pink tinge. Female Common Mergansers have a reddish-brown head that contrasts with a white patch on the chin and breast.
The Red-breasted Merganser (Mergus serrator) is a medium-sized species, smaller and more slender than the Common Merganser. The male is identified by his dark metallic green head, a shaggy, double-pointed crest, and a prominent reddish-brown chest band. Females have a brownish head with a shaggy crest, lacking the distinct white chin patch seen on the female Common Merganser.
The Hooded Merganser (Lophodytes cucullatus) is the smallest, characterized by its large, fan-shaped crest. The male’s crest is black with a large white patch, which he can raise or lower. Female Hooded Mergansers have a tawny-cinnamon crest and head, with a dark gray-brown body. This species is the only merganser native exclusively to North America.
Feeding Behavior and Aquatic Habitats
Mergansers are specialized piscivorous predators. Their diet mainly consists of small to medium-sized fish, such as minnows, trout, and sculpins. They supplement this diet with aquatic invertebrates, including crayfish, insects, and mollusks.
They hunt by swimming along the water’s surface, often dipping their heads in to peer below until they spot a target. Once prey is sighted, they dive to pursue it underwater, using their powerful feet for propulsion. Mergansers prefer clear water, typically less than four meters deep, as they rely heavily on sight to locate their food.
Preferred habitats vary by species and season, though they are generally associated with rivers and lakes in forested areas. Common Mergansers favor freshwater rivers and large inland lakes, often nesting in tree cavities near the water. Red-breasted Mergansers are the most adapted to marine life and are frequently found in coastal estuaries, bays, and saltwater during the winter months. Hooded Mergansers tend to prefer smaller, more secluded bodies of fresh water, such as wooded swamps and ponds.