Common Merganser
Mergus merganser

Overview

Key Features:

The Common Merganser is a large, streamlined, narrow-billed, cold-hardy, fish-eating duck that nests worldwide near large lakes and rivers in northern forested habitats. In flight, more elongated than other ducks, with a flat, pointed profile, flying in trailing lines close to the water's surface.

Similar Species:

Red-breasted Merganser (Mergus serrator)
Hooded Merganser (Lophodytes cucullatus)

Primary Common Name:

Common Merganser

Synonymous name(s):

sawbill, fish duck, sheldrake, gooseander

General Grouping:

Seabirds and shorebirds

Geographic Range:

Worldwide throughout the arctic and subarctic

Common Mergansers occur worldwide throughout the arctic and subarctic, nesting within the boreal forest tree line area and along ocean coasts. In North America, they breed across the continent from interior Alaska to Newfoundland, south throughout the Acadian and Great Lake forest regions, Aspen Parklands and Montane Forest. They are typically found along river and coastal areas where trees are large enough to provide cavities for nesting. During winter, Common Mergansers remain as far north as open water is available, and are most frequently found on fresh water lakes, rivers, and reservoirs, predominantly in coastal areas of Alaska, Canada and the United States and also fresh water areas across the continental United States and into northern Mexico. They also breed in northern Europe, Scandinavia, throughout Russia, and in much of northern Asia. Populations in Europe winter along the coasts of Scandinavia and northern Europe, as well as parts of the northern Mediterranean coast and north Africa. In Asia Common Mergansers winter in southern Asia, northern India, Japan, China, and Korea.

Habitats:

estuary, protected rocky shore

Notes:

Common Mergansers occur worldwide throughout the arctic and subarctic, nesting within the boreal forest tree line area and along ocean coasts. In North America, they breed across the continent from interior Alaska to Newfoundland, south throughout the Acadian and Great Lake forest regions, Aspen Parklands and Montane Forest. They are typically found along river and coastal areas where trees are large enough to provide cavities for nesting.

Abundance:

Relative Abundance:

The Common Merganser is uncommon but present year round in Monterey County. Nesting populations are found along the upper Carmel, upper Salinas, Big Sur, Little Sur, Arroyo Seco, San Antonio, and Naciemento rivers. It is rare along the coast. Surveys during 1970-'79, suggested a continental population of 1.5 million birds. Later surveys suggest numbers from 600,000 to 1 million. Currently, accurate population information does not exist for common mergansers. However, populations are thought to be stable.

Species Description:

General:

The Common Merganser is a large, streamlined, cold-hardy, fish-eating duck that nests worldwide near large lakes and rivers in northern forested habitats They are among the largest ducks, but are less stocky than eiders and goldeneyes. In flight, they appear more elongated than other ducks, with a flat, pointed profile, flying in trailing lines close to the water's surface. Adult sexes are strongly dimorphic in size and plumage most of year. Male common mergansers are larger than females. In breeding season they have an iridescent greenish-black head and upper neck. The lower neck, breast and underparts are creamy-white with a variable pink wash. They have black backs and upperwing coverts with white shoulder feathers. The long (6 cm), narrow bill is thick at its base, tapering to a point, and is red with a blackish upper ridge, and a hooked upper mandible and fine, saw-like teeth along the edges, and scarlet-orange lining to mouth. The legs are red to brownish-red, brightest on adult males, dullest on juveniles. Eyes are brown. In nonbreeding season the male is similar to the female, who has a tufted cinnamon-brown head with a whitish chin. The back and sides are silver-gray and the breast and belly are white. The bill, feet, and eyes are the same as the male. In summer look for females leading ducklings along streams or standing on a rock midstream. Juveniles are similar to adult females but show a short black-edged white stripe between the eye and bill. Females have a call that is deep, harsh, and croaking kar-r-r, sometimes accelerating to a cackling kokokoko. Males give hoarse croaking notes and in display have a faint twanging or bell-like single note. Generally, they are wary and one or more birds stay on sentry duty to warn the flock of danger. When disturbed, they often disgorge food before moving. Though they move clumsily on land, they will resort to running if alarmed, assuming a very upright position similar to penguins, falling and stumbling frequently as they run to the water to fly or dive. In order to rise from water, they flap along the surface for many yards. Once they are airborne the flight is strong and rapid. Occasionally adults perch on tree limbs near water, and both males and females come out on rocks, sandbars, and ice to rest and preen. Adults may spend nights ashore where undisturbed, but most often sleep on the water.

Distinctive Features:

The Common Merganser is a large, streamlined, narrow-billed, cold-hardy, fish-eating duck that nests worldwide near large lakes and rivers in northern forested habitats. In flight, more elongated than other ducks, with a flat, pointed profile, flying in trailing lines close to the water's surface.

Size:

Length: 58–72 cm (23–28 in) Wingspan: 78–97 cm (31–38 in) Weight: 0.9–2.1 kg (2.0–4.6 lb)

Natural History:

General:

The Common Merganser winters on large lakes, rivers, and reservoirs of north central United States and along the coasts. It generally nests further north near fresh water in tree cavities or nest boxes but will nest on the ground or in crevices. Females breed in their second year, generally laying one clutch of 9 to 12 white eggs per year, which they may lay in the nests of other cavity-nesting ducks. See SEASONAL BEHAVIOR for details.

Predator(s):

Man is the main predator of the Common Merganser, as they are still hunted. After leaving the nest, the young are in danger from hawks, owls, Bald Eagles, Golden Eagles, Common Loons, and even fish such as northern pike. They escape from predators by running on the surface of the water or skulking under banks.

Prey:

Common Mergansers eat mainly fish, amphibians, crustaceans, mollusks and other invertebrates obtained by diving underwater in marine and freshwater habitats. Its long, narrow beak has tooth-like serrations that help it grasp slippery prey. It has been recorded swallowing large fish up to 30 cm or more in length. Diet varies with habitat and geographic location. They forage primarily on small fish, including salmon, trout, suckers, sculpin, sticklebacks, shad, chub, and minnows. They are also known to forage on aquatic invertebrates, frogs, small mammals, birds, and plants. Downy young eat mostly aquatic invertebrates such as caddis flies, mayflies, backswimmers, flies, water striders, dragonflies, and seeds but switch to fish when about 12 days old.

Feeding Behavior:

Carnivore, Omnivore

Notes:

Common mergansers are diving predators that locate their prey by sight, and therefore tend to feed in clear water, less than 4 m deep, including estuaries, coastal bays, lakes, streams, and rivers. In the winter, they have been known to dive deeper in order to capture schooling fish. They can also find prey by probing underwater crevices and sediments when the water is cloudy. They feed most actively in the early morning after dawn, in the afternoon, and before sunset. When on the surface they swim forward with head underwater searching and submerging to capture prey. If the water is shallow they will surface to swallow prey but in deeper water will swallow fish while still submerged. In larger streams and rivers small groups float down stream for a couple of miles, and either fly back again or more commonly fish their way back, diving incessantly the whole way. In smaller streams, they are present in pairs or smaller groups, and float down, twisting round and round in the rapids, or fishing vigorously in some deep pool near the foot of a waterfall. During migration and winter, flocks of hundreds of Common Mergansers may forage cooperatively by driving fish ahead of them. Common Mergansers are considered keystone predators, acting to control the populations of many inland fish such as perch and bass. By thinning these populations, it is thought that mergansers help to keep them healthy and growing. Wilderness lakes where mergansers feed generally produce larger, healthier fish than lakes without predation.

Seasonal Behavior

February - March

Migration:

Common Mergansers wintering in California move north by March along the British Columbia coast. They are often the first waterfowl to return north in the spring and the last to move south in the fall, usually migrating along major rivers, lake chains, and coastlines during day and overland by night. They are partial migrants, moving away from areas where rivers and major lakes freeze in the winter, but resident where waters remain open. Eastern North American birds move south in small groups to the United States wherever ice free conditions exist on lakes and rivers; on the milder Pacific coast, they are permanent residents. During summer, nonbreeders remain in small numbers at many locations throughout the winter range. There is little information on distances of nonstop flights or speeds attained. They migrate in small, scattered flocks of 3–9 birds usually, but may form larger flocks when on large lakes, reservoirs, or estuaries. Their flight is straight and direct in structured flocks.

April - September

Reproduction:

Common mergansers breed from Alaska, the southern Yukon, Labrador and Newfoundland south to central California, Arizona, New Mexico, southern Chihuahua and east of the Rockies to Minnesota, Michigan, New York, New England and Nova Scotia. Males vocalize during courtship, producing several calls: a faint, high-pitched, bell-like note during display; a twanging neck stretch, and a kragagagagaga during courtship flight. They arrive on breeding areas in April and May and egg laying begins about 2 weeks after arrival. Females select the nest site and often return to the same site from previous years. Males remain near nest site into the incubation period and then depart for molting locations in larger lakes, bays, and rivers. They have only one brood per season. Females usually start breeding in their second year. Pair bonds form in late winter or early spring. Nests are located near water, usually in a large tree cavity, but may also be in rock crevices, under tree roots, or in nest boxes. Nests are made of wood chips and other debris plus down added by the female. She usually lays 9 to 12 relatively large (64mm) white to yellowish eggs over a two week period. Brood parasitism, or egg-dumping, is fairly common between individual Common Mergansers, as well as between other related species. Common Mergansers have been known to place their eggs in the nests of Common Goldeneyes and Hooded Mergansers. And both Common Goldeneyes and Hooded Mergansers have also been known to place their eggs in the nests of Common Mergansers. This can lead to mixed clutches of up to 19 eggs. Incubation lasts from 28 to 35 days, and is done by the female alone. The young are precocial and jump from the cavity within a day or so of hatching and head for the water. Females give a high pitched, rapid cro cro cro when calling the young from the nest and hiss if cornered. They lead the young to food. The young can feed themselves, catching freshwater invertebrates and small fish fry, mostly by dabbling at first, but after a week can dive well. Females usually abandon the young before they can fly, sometimes as early as the end of the first week. Broods often join together in crèches after they are about a week old. They fledge when 60–70 days old. The young are sexually mature at two years old.

August - November

Migration:

Most Common Mergansers migrate short to medium distances in small groups. The post-breeding molt migration of males is not well understood, but it is thought that they migrate north to large lakes, bays, and rivers. Females molt alone after they leave their broods. The young migrate last after fledging. They are partial migrants, moving away from areas where rivers and major lakes freeze in the winter, but resident where waters remain open. Eastern North American birds move south in small groups to the United States wherever ice free conditions exist on lakes and rivers. On the milder Pacific coast, they may be permanent residents or pairs and flocks begin to move through British Columbia in late Oct, peaking in November; farther south in California, some local birds begin to arrive in Central Basin lakes in September and increase through late November; numbers generally decline through December in California. Many common mergansers are still found in central Canadian provinces during the Christmas Bird Count and year-round in s. Quebec and early in the spring.

November - March

Feeding:

Immatures and adult males appear first on wintering grounds as soon as open water is available, followed by females a few weeks later. Adult males seem to winter farther north than females and juvenile birds. They range along the Atlantic coast from Newfoundland almost to Florida, in the interior from the Great Lakes to the Gulf of Mexico and on the Pacific coast from the Aleutian Islands to Mexico. Primary winter habitats are large lakes, reservoirs, rivers, as well as coastal bays, estuaries and harbors of the Atlantic and Pacific, wherever adequate food is found, but tending to winter on fresh water. Pairs are formed in late winter, and until then flocks are usually composed entirely of males or of females. They often form large rafts, or floating flocks, in the winter.

Issues

Monterey Bay National Marine Sanctuary:

Common Merganser populations are most limited by the availability of nesting sites, such as tree cavities. Thus logging can have a detrimental effect when large trees suitable for nesting are removed. Nest boxes installed by humans have improved populations in some areas. Because of the merganser's fish diet, it is an important indicator of contamination pathways and health of aquatic ecosystems. Elevated levels of various contaminants, including PCB, DDE, dieldrin, dioxins, furans, and mercury have been found in merganser tissues in the Great Lakes and other sites. In some instances, levels of mercury in mergansers were a possible risk for human consumption and for reproduction of the birds. It is subject to persecution by anglers and fish-farmers who accuse it of depleting fish stocks, and it is occasionally drowned in freshwater fishing nets. It is also threatened by the degradation of freshwater lakes through drainage and petroleum pollution in Russia and as a result of acid rain in North America. It is also susceptible to avian influenza so may be threatened by future outbreaks of the virus. It is hunted in North America and Russia, although it is not a popular game bird, and its eggs used to be, and possibly still are, harvested in Iceland. Overall, this is one of least studied ducks in North America and much remains to be learned to for effective management. Current IUCN status is Least Concern

References

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