Common mergansers are skilled diving predators, eating mainly slower small fish. Their serrated bills are well suited for capturing small fish and other aquatic prey. Clear water is preferred for feeding because the birds hunt primarily by sight. When fish are scarce (usually in spring), mergansers will substitute other small aquatic prey such as insects, frogs, and snails. They have been known to eat aquatic plants in some instances, and to feed on trout from freshwater streams when nearby ponds and lakes freeze. These birds feed most actively in the early morning after dawn, in the afternoon, and before sunset.
Animal Foods: amphibians; fish; insects; mollusks; aquatic or marine worms
Plant Foods: macroalgae
Primary Diet: carnivore (Piscivore )
Common mergansers are generally considered to be top predators in aquatic food chains. Predation rates are very low, and their offspring survival rate is good, largely because Mergus merganser typically nests far enough north that most common nest predators are not a threat. The nest predators that live far enough north to potentially be a threat to Mergus merganser include red squirrels, American martens, northern flickers, and black bears. Large predatory fish such as northern pike, along with predatory birds such as bald and golden eagles, common loons, and some owls and hawks, may prey on more vulnerable, immature mergansers. However, no predators of common mergansers have been documented.
Common mergansers are the largest mergansers and the largest North American inland ducks. Males are slightly larger, on average. Males and females are colored quite differently. Males have bright, vivid, solid areas of color with sharply defined edges; black back, dark green to black head (changes to brown in non-breeding season), serrated red bill, red feet, and white, cylindrical body with slight peach-colored tinge on breast, and fading to some grey in the tail. Male common mergansers have no visible crest. Males can be readily distinguished from male common goldeneyes, which have shorter necks, rounded bodies, more ruffled heads, and white eyes. Female common mergansers have the same red feet and bill as males, but they have a larger crest, a brown head, and the body is a less sharply defined mixture of grey and white, fading to white in the breast. The line between the brown neck and white breast is sharply defined, which distinguishes female common mergansers from similar female red-breasted mergansers.
Adults have an average basal metabolic rate of 638 kJ/d. Field metabolic rates, studied in autumn in Scotland, were found to be higher in females than males, with an overall average of 2.32 ml CO2/h.
Range mass: 1050 to 2054 g.
Range length: 53 to 69 cm.
Range wingspan: 86 to 99 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently
The record for the oldest common merganser is held at 13 years 5 months, but banding records indicate maximum longevities of approximately 12 years 6 months for males and 13 years 10 months for females.
Range lifespan
Status: wild: 13.8 (high) years.
Range lifespan
Status: captivity: 13.4 (high) years.
Average lifespan
Status: wild: 161 months.
Common mergansers prefer to live in wooded areas along streams and rivers or near small, inland lakes. They can also be found along the shores of the Great Lakes, as well as on coastal streams in British Columbia. Nests are typically in a crevice of a deciduous tree along the shore, but sometimes will be in other types of crevices or on the ground, under tangled bushes. Mergansers may also occupy abandoned hawk nests when available.
Common mergansers are diving predators who locate their prey by sight, and therefore tend to feed in clear waters, less than 4 m deep, including estuaries, coastal bays, lakes, streams, and rivers. In the winter, common mergansers have been known to dive deeper in order to capture schooling fish.
Range depth: 4 (high) m.
Habitat Regions: temperate ; terrestrial ; freshwater
Terrestrial Biomes: forest ; mountains
Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water
Other Habitat Features: riparian ; estuarine
Mergus merganser (common mergansers or goosanders) occur in both the Nearctic and Palearctic regions. Although their abundance has been decreasing in North America, they are still the most abundant of the mergansers found there. In North America, common mergansers may breed as far north as southern Alaska and Canada. Some occur year-round in the northern and western United States. North American birds winter in New England, midwestern and southern states, and the Pacific coast of the U.S. and Canada. Common mergansers in the Palearctic region typically 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.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native )
Other Geographic Terms: holarctic
Mergus merganser is considered a keystone predator, acting to control the populations of many inland fish such as perch and bass. By thinning these populations, it is thought that mergansers keep lakes and ponds below their carrying capacity. This allows those fish that survive to thrive and grow, whereas in lakes and ponds lacking the merganser predation, fish are often too prolific and bring about their own growth stagnation. Thus, wilderness lakes where mergansers feed generally produce larger, healthier fish than lakes without predation, where no individual fish grow very well because of overcrowding.
Brood parasitism, or egg-dumping, is fairly common between individual common mergansers, as well as between Mergus merganser and other related species. Common mergansers have been known to parasitize and be parasitized by both common goldeneyes and hooded mergansers. This has been shown to lead to mixed clutches of up to 19 eggs.
Ecosystem Impact: keystone species
Species Used as Host:
Commensal/Parasitic Species:
Fish that have to compete in overpopulated lakes and ponds often do not grow very large. By thinning fish populations in lakes and ponds, common mergansers allow the remaining fish to thrive, because they have less competition for the habitat's limited resources. Thus, more fish reach legal size for fishermen, who benefit indirectly from this form of population control provided by the mergansers. Common mergansers are also attractive birds that attract ecotourism attention.
Positive Impacts: food ; ecotourism
Common mergansers have no known negative effects on humans.
Common mergansers remain common in both the Palearctic and Nearctic regions, and are not thought to be threatened at this time.
The limiting factor on Mergus merganser populations seems to be nesting site availability. Thus, urbanization and human civilization are thought to be the causes for common mergansers moving breeding sites farther south in the southeastern United States (recorded as far south as Virginia in the last 50 years) as former habitats are destroyed due to human development. However, nest boxes installed by humans have provided additional suitable nesting sites in some areas.
Although North American populations seem to have declined somewhat over the last 200 years, they remain large and may now be increasing. In Europe, deforestation is thought to be a cause of some breeding range reduction, but populations continue to thrive and grow throughout Eurasia, especially in Scotland, Ireland, and Wales.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Common mergansers use their keen eyesight to locate prey underwater while swimming on the surface, but can also revert to probing underwater crevices when the water is cloudy. Males are typically only vocal during courtship, and have several calls, including hoarse croaking sounds and a twang somewhat like a guitar string. Females are also predominantly silent, vocalizing only in courtship or as a warning of danger. The females have a harsh karr, karr call. Aerial chases, in which 2 or more birds dive from flight into the water with a particular body posture to produce an audible hollow sound, have been reported, but their purpose is unknown.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Common mergansers form monogamous mating pairs that last for at least one mating season. The duration of these loyalties is unknown, but pairs reunite over years in other duck species. Pairs are formed in late winter, when a male circles a female and displays the Courtship-Intent Posture, with neck stretched forward and head feathers erect.
Mating System: monogamous
Common mergansers breed once per year, in the summer. A clutch typically contains 9 to 12 eggs, which are laid between May and June. Eggs are approximately 64 mm in length and have a pale yellow, ivory, or white buff appearance. Upon hatching, young birds follow their mothers to feeding sites. Often the mother will lead the brood to larger bodies of water downstream to feed. Young can swim and feed easily as soon as they leave the nest, although for the first few days most food is obtained on the surface. Within about 8 days, the young are skillful divers. Mothers abandon their broods before the young develop the ability to fly, typically 30 to 50 days after hatching. Young mergansers commonly join other broods after being abandoned; mixed broods of more than 40 young have been observed.
Breeding interval: Common mergansers breed once yearly.
Breeding season: Breeding occurs from May to June each year.
Range eggs per season: 6 to 17.
Average eggs per season: 8-12.
Range time to hatching: 28 to 35 days.
Range fledging age: 60 to 85 days.
Average time to independence: 30-50 days.
Range age at sexual or reproductive maturity (female): 2 (low) years.
Range age at sexual or reproductive maturity (male): 2 (low) years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Average eggs per season: 10.
Male parents typically leave the breeding grounds when incubation begins, and female parents incubate the eggs for 28 to 35 days. Young are precocial, and leave the nest within 24 to 48 hours. When the nest is in a tree cavity, this departure is accomplished by jumping to the ground. For the next few weeks, females can be seen leading their chicks to feeding sites as far away as 8 km, although once they arrive there, the young are responsible for finding their own food. The mother may give warnings of potential dangers, to which the young are quite responsive, but otherwise the young are fairly independent at the feeding site. They are skilled divers within 8 days of leaving the nest, until then they dabble on the surface to find food. Mothers abandon their offspring before the young birds develop the ability to fly.
Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Protecting: Female); pre-independence (Protecting: Female)
A large (22-27 inches) duck, the male Common Merganser is most easily identified by its green head, pale body, and thin red bill. The female Common Merganser is gray above and pale below with a rusty head and crest. In flight and at a distance, both sexes may be distinguished from the related Red-breasted Merganser (Mergus serrator) by the former species’ larger size and paler overall body pattern. Duck hunters often call mergansers “saw-bills” in reference to their long, thin, serrated bills. The Common Merganser has a wide distribution across the Northern Hemisphere. In North America, this species breeds across southern Alaska, Canada, and the northern United States. Smaller populations occur further south at higher elevations, particularly in the western U.S., where this species breeds locally south to Arizona and New Mexico. In winter, all populations migrate south, and may be found in coastal Alaska and Canada, in much of the U.S. outside of the southeast and northern Great Plains, and in northern Mexico. In the Old World, this species breeds across northern Europe, Scandinavia, and Russia, wintering south to North Africa, India, and Southeast Asia. As this species generally nests in tree cavities, Common Mergansers primarily breed on small bodies of water surrounded by woodland. In winter, this species may be found on large bodies of freshwater, including lakes, rivers, bays, and freshwater portions of large estuaries. Common Mergansers eat small animals, primarily fish and aquatic invertebrates. As this species is one of several “diving ducks,” Common Mergansers may be observed submerging themselves to feed in the water or on the bottom. In winter, they may also be observed in small flocks on large bodies of water. Like other mergansers, the Common Merganser undertakes swift, straight flights between bodies of water or on migration. This species is primarily active during the day.
A large (22-27 inches) duck, the male Common Merganser is most easily identified by its green head, pale body, and thin red bill. The female Common Merganser is gray above and pale below with a rusty head and crest. In flight and at a distance, both sexes may be distinguished from the related Red-breasted Merganser (Mergus serrator) by the former species’ larger size and paler overall body pattern. Duck hunters often call mergansers “saw-bills” in reference to their long, thin, serrated bills. The Common Merganser has a wide distribution across the Northern Hemisphere. In North America, this species breeds across southern Alaska, Canada, and the northern United States. Smaller populations occur further south at higher elevations, particularly in the western U.S., where this species breeds locally south to Arizona and New Mexico. In winter, all populations migrate south, and may be found in coastal Alaska and Canada, in much of the U.S. outside of the southeast and northern Great Plains, and in northern Mexico. In the Old World, this species breeds across northern Europe, Scandinavia, and Russia, wintering south to North Africa, India, and Southeast Asia. As this species generally nests in tree cavities, Common Mergansers primarily breed on small bodies of water surrounded by woodland. In winter, this species may be found on large bodies of freshwater, including lakes, rivers, bays, and freshwater portions of large estuaries. Common Mergansers eat small animals, primarily fish and aquatic invertebrates. As this species is one of several “diving ducks,” Common Mergansers may be observed submerging themselves to feed in the water or on the bottom. In winter, they may also be observed in small flocks on large bodies of water. Like other mergansers, the Common Merganser undertakes swift, straight flights between bodies of water or on migration. This species is primarily active during the day.
The common merganser (North American) or goosander (Eurasian) (Mergus merganser) is a large seaduck of rivers and lakes in forested areas of Europe, Asia, and North America. The common merganser eats mainly fish. It nests in holes in trees.
The first formal description of the common merganser was by Swedish naturalist Carl Linnaeus in 1758 in the 10th edition of his Systema Naturae. He introduced the current binomial name Mergus merganser.[2] The genus name is a Latin word used by Pliny and other Roman authors to refer to an unspecified waterbird, and merganser is derived from mergus and anser, Latin for "goose".[3] In 1843 John James Audubon used the name "Buff-breasted Merganser" in addition to "goosander" in his book The Birds of America.[4]
The three subspecies differ in only minor detail:[5][6]
It is 58–72 cm (23–28+1⁄2 in) long with a 78–97 cm (30+1⁄2–38 in) wingspan and a weight of 0.9–2.1 kg (2 lb 0 oz – 4 lb 10 oz); males average slightly larger than females, but with some overlap. Like other species in the genus Mergus, it has a crest of longer head feathers, but these usually lie smoothly rounded behind the head, not normally forming an erect crest. Adult males in breeding plumage are easily distinguished, the body white with a variable salmon-pink tinge, the head black with an iridescent green gloss, the rump and tail grey, and the wings largely white on the inner half, black on the outer half. Females and males in "eclipse" (non-breeding plumage, July to October) are largely grey, with a reddish-brown head, white chin, and white secondary feathers on the wing. Juveniles (both sexes) are similar to adult females but also show a short black-edged white stripe between the eye and bill. The bill and legs are red to brownish-red, brightest on adult males, dullest on juveniles.[5][6][7]
Like the other mergansers, these piscivorous ducks have serrated edges to their bills to help them grip their prey, so they are often known as "sawbills". In addition to fish, they take a wide range of other aquatic prey, such as molluscs, crustaceans, worms, insect larvae, and amphibians; more rarely, small mammals and birds may be taken.[5][6] As in other birds with the character, the salmon-pink tinge shown variably by males is probably diet-related, obtained from the carotenoid pigments present in some crustaceans and fish.[8] When not diving for food, they are usually seen swimming on the water surface, or resting on rocks in midstream or hidden among riverbank vegetation, or (in winter) on the edge of floating ice.[5][6]
In most places, the common merganser is as much a frequenter of salt water as fresh water. In larger streams and rivers, they float down with the stream for a few 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 they float down, twisting round and round in the rapids, or fishing vigorously in a deep pool near the foot of a waterfall or rapid. When floating leisurely, they position themselves in water similar to ducks, but they also swim deep in water like cormorants, especially when swimming upstream. They often sit on a rock in the middle of the water, similar to cormorants, often half-opening their wings to the sun. To rise from water, they flap along the surface for many yards. Once they are airborne, their flight is strong and rapid.[9] They often fish in a group forming a semicircle and driving the fish into shallow water, where they are captured easily. Their ordinary voice is a low, harsh croak, but during the breeding season, males in display, as well as young, make a plaintive, soft whistle. Generally, they are wary, and one or more birds stay on sentry duty to warn the flock of approaching danger. When disturbed, they often disgorge food before moving.[10] Though they move clumsily on land, they resort to running when pressed, assuming a very upright position similar to penguins, and falling and stumbling frequently.[11]
Nesting is normally in a tree cavity, so it requires mature forest as its breeding habitat; they also readily use large nest boxes where provided, requiring an entrance hole 15 cm (6 in) in diameter.[12] In places devoid of trees (like Central Asian mountains), they use holes in cliffs and steep, high banks, sometimes at considerable distances from the water.[10] The female lays 6–17 (most often 8–12) white to yellowish eggs, and raises one brood in a season. The ducklings are taken by their mother in her bill to rivers or lakes immediately after hatching, where they feed on freshwater invertebrates and small fish fry, fledging when 60–70 days old. The young are sexually mature at the age of two years.[5][6][7] Common mergansers are known to form crèches, with single females having been observed with over 70 ducklings at one time.[13]
The species is a partial migrant, with birds 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. Scandinavian and Russian birds also migrate southwards, but western European birds, and a few in Japan, are largely resident.[5][6] In some populations, the males also show distinct moult migration, leaving the breeding areas as soon as the young hatch to spend the summer (June to September) elsewhere. Notably, most of the western European male population migrates north to estuaries in Finnmark in northern Norway (principally Tanafjord) to moult, leaving the females to care for the ducklings. Much smaller numbers of males also use estuaries in eastern Scotland as a moulting area.[7][14][15]
Overall, the species is not threatened, though illegal persecution by game-fishing interests is a problem in some areas.[16] In February 2020, a rare common merganser sighting was documented in Central Park, New York; the bird was in obvious distress, with its beak being trapped by a piece of debris.[17]
Within western Europe, a marked southward spread has occurred from Scandinavia in the breeding range since about 1850, colonising Scotland in 1871, England in 1941, and also a strong increase in the population in the Alps.[7] They are very scarce in Ireland, with regular breeding confined to a few pairs in County Wicklow.[18]
The goosander is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds applies.
Female goosander's bill showing the serrated edge
_-_Mergus_merganser_IMG_9145.JPG)
Couple and single female on the Jona in Switzerland
M. m. americanus, female and juveniles
Egg, Collection Museum Wiesbaden
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Robert Wilkinson Padley - A Goosander, 1817
The common merganser (North American) or goosander (Eurasian) (Mergus merganser) is a large seaduck of rivers and lakes in forested areas of Europe, Asia, and North America. The common merganser eats mainly fish. It nests in holes in trees.
