Red-breasted mergansers are found throughout much of the northern hemisphere. They have separate breeding and wintering ranges, although they are found year-round in some northern, coastal areas. In the Americas they breed from Alaska throughout northern Canada to the Atlantic ocean and into the northern United States: Minnesota, Wisconsin, Michigan, and Maine. They breed in Greenland and Iceland and in Eurasia from the Faroe Islands, Ireland, and Scotland through Scandinavia, northern Russia and Asia to Siberia and the Kamchatka Peninsula. Red-breasted mergansers winter in coastal areas, including the Atlantic, Pacific, Gulf of Mexico, Great Lakes coasts, and other large, inland waterways as far south as northern Mexico in the Americas and the Baltic, North, Mediterranean, Black, Caspian, and Aral Seas in Eurasia.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); arctic ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: holarctic

Red-breasted mergansers have a holarctic distribution; they are found throughout much of the northern hemisphere. Red-breasted mergansers have distinct breeding and wintering ranges, although they overlap somewhat in northern, coastal areas. In the Americas they breed from Alaska throughout northern, boreal Canada to the maritime provinces and into the northern United States: Minnesota, Wisconsin, Michigan, and Maine. They breed in Greenland and Iceland and in Eurasia from the Faroe Islands, Ireland, and Scotland through Scandinavia, northern Russia and Asia to Siberia and the Kamchatka Peninsula. They may also breed in northeastern China, northern Japan, and as far south as northern Germany, Lake Baikal, Manchuria, and the Sea of Okhotsk. Red-breasted mergansers winter in coastal areas, including the Atlantic, Pacific, Gulf of Mexico, Great Lakes coasts, and other large, inland waterways as far south as northern Mexico in the Americas and the Baltic, North, Mediterranean, Black, Caspian, and Aral Seas in Eurasia. They sometimes wander as far south as portions of the Red Sea and to the Hawaiian Islands in winter. They are found throughout the year in northern coastal areas, including Iceland, parts of the British Isles, southeastern Alaska and the Aleutian Islands, coastal areas of Maine and the Canadian maritime provinces, and the northernmost lower peninsula of Michigan and northern shore of Lake Michigan.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); arctic ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: holarctic

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: northern Alaska to Baffin Island and Newfoundland, south to Aleutians, southeastern Alaska, northern Alberta, Minnesota, Michigan, northern New York, northern Vermont, Maine, and Nova Scotia. NON-BREEDING: southern Alaska, Great Lakes, and Nova Scotia to Baja California, Gulf Coast, Florida; very rare in Hawaii. Winters primarily in coastal waters (especially the Atlantic coast from Maine to North Carolina, the Gulf coast along the Florida panhandle, and around Vancouver Island) but also in many inland areas (including especially southern Lake Huron and northern Utah) (Root 1988). Also breeds and winters in the Old World.

Red-breasted mergansers are large diving ducks with long, thin bills lined with serrated edges to help in capturing fish prey. Males are larger than females. Lengths range from 51 to 64 cm and weights from 800 to 1350 g. In their breeding plumage, males are more colorful, with dark greenish heads, a white collar, brown-speckled breasts, steel-gray flanks, and greenish-black backs that are bordered by a white patch. Both females and males have a double crest of plumes at the back of their heads. Females are grayish brown, with a small, white wing bar, a whitish breast with gray speckles, and the feathers on the head are reddish brown. The bill and legs are reddish-orange and the bill has a black tip. Females stays the same throughout the year and immature birds resemble females. Males in the non-breeding season resemble females but have wider, white wing bars.

Range mass: 800 to 1350 g.

Range length: 51 to 64 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger; male more colorful

Red-breasted mergansers are relatively large diving ducks with long, thin bills lined with serrated edges to help in capturing fish prey. Males are larger than females. Lengths range from 51 to 64 cm and weights from 800 to 1350 g. In their breeding plumage, males are more colorful, with dark greenish heads, a white collar, brown-speckled breasts, steel-gray flanks, and greenish-black backs that are bordered by a white patch. Both females and males have an asymmetrical crest of plumes at the back of their heads. Females are grayish brown overall, with a small, white wing bar, a whitish breast with gray speckles, and the head is cinnamon brown. There is an inconspicuous white eye ring. The bill and legs are reddish-orange and the bill has a black tip. Female plumage stays the same throughout the year and immature birds resemble females. Males in the non-breeding season resemble females but have wider, white wing bars.

Range mass: 800 to 1350 g.

Range length: 51 to 64 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger; male more colorful

Length: 58 cm

Weight: 1135 grams

See Kaufman (1990) for information on identification.

Red-breasted mergansers are found on wetlands and open bodies of freshwater, brackish, or saltwater. In summer they are found in northern areas, usually coasts, lakes, and rivers near conifer forests or tundra. In winter and during migration they are found on protected waters along sea coasts and large, inland lakes and rivers. Red-breasted mergansers forage mainly in shallow waters with submergent vegetation and abundant fish prey.

Habitat Regions: temperate ; saltwater or marine ; freshwater

Terrestrial Biomes: tundra ; taiga ; forest

Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water

Other Habitat Features: estuarine

• Terrestrial
• Freshwater
• Marine

Red-breasted mergansers are found on wetlands and open bodies of freshwater, brackish, or saltwater in their breeding and wintering ranges. In the breeding range, they are found in the tundra and boreal zones. In winter and during migration they are found on protected waters along sea coasts and large, inland lakes and rivers, although they also use fast-flowing rivers. Red-breasted mergansers are found foraging mainly in shallow waters with submergent vegetation, although they also forage in deep waters, just as long as there is an abundance of their fish prey.

Habitat Regions: temperate ; saltwater or marine ; freshwater

Terrestrial Biomes: tundra ; taiga ; forest

Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water

Other Habitat Features: estuarine

Comments: BREEDING: Rivers, ponds, lakes, and coastal areas (AOU 1983). Nests along inland waters, generally on ground on small islands with low vegetative cover, and also near seacoast and occasionally on shores of ocean or on coastal islands. NON-BREEDING: winters mainly in estuaries and sheltered bays, less frequently on large inland bodies of water (AOU 1983).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Migrates north mostly March-May; arrives in northernmost breeding areas late May-early June. Southward migration mostly September-December. Some coastal breeding populations may stay in area all year? (Palmer 1976).

Red-breasted mergansers eat mainly small Actinopterygii (10 to 15 cm long) and Crustacea. Their diet is usually made up of more than 75% small fish, with less than 25% made up of crustaceans and other aquatic animals, including insects, worms, and amphibians. They seem to prefer foraging in shallow water, but they will hunt wherever prey is abundant. Red-breasted mergansers forage in several different ways. They float at the surface, looking underwater as they go, they dive in deep or shallow water to search for prey, or they dive in formation with other red-breasted mergansers to herd schooling prey. Preferred fish prey include Fundulus, Gasterosteidae, Salmo salar, Cottus, Clupea pallasi and their eggs, Oncorhynchus, Menidia menidia, and Alosa aestevalis.

Animal Foods: amphibians; fish; eggs; aquatic or marine worms; aquatic crustaceans

Red-breasted mergansers eat mainly small fishes (10 to 15 cm long) and crustaceans. Their diet is usually made up of over 75% small fish, with less than 25% made up of crustaceans and other aquatic animals, such as insects, worms, and amphibians. They seem to prefer foraging in shallow water, but they will hunt wherever prey is abundant. Red-breasted mergansers forage in several different ways. They float at the surface, looking underwater as they go, they dive in deep or shallow water to search for prey, or they dive in formation with other red-breasted mergansers to herd schooling prey. This cooperative foraging strategy can be very effective and has been observed when mergansers are hunting sheepshead minnows. Other preferred fish prey include killifishes, sticklebacks, Atlantic salmon, sculpins, herring and their eggs, salmon eggs, silversides, and blueback herring.

Animal Foods: amphibians; fish; eggs; aquatic or marine worms; aquatic crustaceans

Primary Diet: carnivore (Piscivore )

Comments: Eats mostly fishes plus some crustaceans; insects are important to young (Palmer 1976). Dives underwater to forage.

Red-breasted mergansers are important predators of small fish in their wetland habitats. Egretta thula, Larus philadelphia, and Larus delawarensis will wait at the surface to grab fish scared by merganser foraging. Red-breasted mergansers are also attracted to areas where Larus are feeding on schooling fish.

Mutualist Species:

• snowy egrets (Egretta_thula)
• Bonaparte's gulls (Larus_philadelphia)
• ring-billed gulls (Larus_delawarensis)

Commensal/Parasitic Species:

• nematodes (Eustrongylides species)
• lice (Anaticola_crassicornis)
• lice (Anatoecus_dentatus)
• lice (Anatoecus_icterodes)
• lice (Holomenopon_loomisi)
• lice (Pseudomenopon species)
• lice (Trinoton_querquedulae)

A wide variety of predators feed on eggs and nestlings of red-breasted mergansers, including Corvus corax, Larus marinus, Larus argentatus, Stercorarius parasiticus, and Neovison vison. Adults have been taken by Bubo virginianus and Falco rusticolis. They may also be taken by Vulpes vulpes and Nyctea scandiaca.

Known Predators:

• common ravens (Corvus_corax)
• great black-backed gulls (Larus_marinus)
• herring gulls (Larus_argentatus)
• parasitic jaegers (Stercorarius_parasiticus)
• mink (Neovison_vison)
• great horned owls (Bubo_virginianus)
• gyrfalcons (Falco_rusticolis)
• red foxes (Vulpes_vulpes)
• snowy owls (Nyctea_scandiaca)

Anti-predator Adaptations: cryptic

Red-breasted mergansers are important predators of small fish in their wetland habitats. Several bird species take advantage of the fact that red-breasted mergansers will herd fish prey to the water's surface when they are foraging. Snowy egrets, Bonaparte's, and ring-billed gulls will wait at the surface to grab fish scared by merganser foraging. Red-breasted mergansers are also attracted to areas where gulls are feeding on schooling fish.

Red-breasted mergansers are parasitized by at least 60 kinds of parasitic worms, including Eustrongylides species, which may cause die-offs. They are also parasitized by ectoparasites, such as lice (Anaticola crassicornis, Anatoecus dentatus, Anatoecus icterodes, Holomenopon loomisi, Pseudomenopon species, and Trinoton querquedulae).

Mutualist Species:

• snowy egrets (Egretta thula)
• Bonaparte's gulls (Larus philadelphia)
• ring-billed gulls (Larus delawarensis)

Commensal/Parasitic Species:

• nematodes (Eustrongylides species)
• lice (Anaticola crassicornis)
• lice (Anatoecus dentatus)
• lice (Anatoecus icterodes)
• lice (Holomenopon loomisi)
• lice (Pseudomenopon species)
• lice (Trinoton querquedulae)

A wide variety of predators feed on eggs and nestlings of red-breasted mergansers, including common ravens, great black-backed gulls, herring gulls, parasitic jaegers, and mink. Adults have been taken by great horned owls and gyrfalcons. They may also be taken by red foxes and snowy owls.

Known Predators:

• common ravens (Corvus corax)
• great black-backed gulls (Larus marinus)
• herring gulls (Larus argentatus)
• parasitic jaegers (Stercorarius parasiticus)
• mink (Neovison vison)
• great horned owls (Bubo virginianus)
• gyrfalcons (Falco rusticolis)
• red foxes (Vulpes vulpes)
• snowy owls (Nyctea scandiaca)

Anti-predator Adaptations: cryptic

Red-breasted mergansers use visual displays and calls during the breeding season to attract mates. They also produce alarm calls that sound like "garr" or "grack."

Communication Channels: visual ; acoustic

Red-breasted mergansers use visual displays and vocalizations in their courtship rituals. They also produce alarm calls that sound like "garr" or "grack." Males produce a drumming sound with their wings during copulation.

Communication Channels: visual ; acoustic

The oldest recorded red-breasted merganser was 9 years and 4 months old. Like many animals, most hatchlings do not survive through their first year. Up to 50% of hatchlings die because of exposure to cold weather, another 25% are preyed on.

Range lifespan

Status: wild: 9.33 (high) years.

The oldest recorded red-breasted merganser was 9 years and 4 months old. A female was also recorded breeding when she was 8 years old. Like many animals, most red-breasted merganser hatchlings do not survive through their first year. Up to 50% of hatchlings die because of exposure to cold weather, another 25% are preyed on. It is thought that about 50% of red-breasted mergansers survive migration and winter to breed the following year.

Range lifespan

Status: wild: 9.33 (high) years.

Red-breasted mergansers form mated pairs each season. Most pair bonds form during spring migration, starting in March. Males use a courtship display and call to attract females. Usually several males display around a single female in an attempt to win her favor.

Mating System: monogamous ; polygynandrous (promiscuous)

Red-breasted mergansers breed relatively late in the season. Mated pairs arrive on the breeding grounds in May and lay eggs in early June. Young hatch in July and can fly by September or October. Females choose nests on land close to water, usually in dense vegetation or under objects. Nests are usually within 23 m of the water. Females start the nest as a scrape, but gradually add grass and feathers throughout incubation. They lay from 5 to 24 beige to gray eggs. Incubation is generally for 30 to 31 days, young hatch synchronously. Young fledge at 60 to 65 days after hatching. Because they breed relatively late, second clutches are unlikely. Most red-breasted mergansers mate first in their third year, although they are mature in their second year.

Breeding interval: Red-breasted mergansers breed once yearly.

Breeding season: Red-breasted mergansers breed in May and June.

Range eggs per season: 5 to 24.

Average eggs per season: 9.5.

Range time to hatching: 30 to 31 days.

Range fledging age: 60 to 65 days.

Range time to independence: 7 (high) weeks.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Average age at sexual or reproductive maturity (female): 3 years.

Range age at sexual or reproductive maturity (male): 2 to 3 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Females incubate the eggs and brood and care for the young until they abandon them within a few weeks after hatching. Males abandon females on the nest soon after she begins incubating the eggs.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Protecting: Female)

Red-breasted mergansers are seasonally monogamous, but there is good evidence that extra-pair copulations may be frequent. Pairs may form as early as November, but most pair bonds form during spring migration, starting in March. Males use a courtship display and call to attract females. Usually several males display around a single female in an attempt to win her favor. Males hold their heads close to their body with the crest raised and their bill pointing up, they then do 1 of 2 alternate displays: the "head shake" and the "salute curtsy." The head shakes involves flicking the head from side to side. In the salute curtsy the male drops the bill forward, then rapidly flicks it up while straightening his neck and raising the chest above the water, the chest is then dropped back into the water, this may also be accompanied by kicking. A "yeow" call is used during the salute portion of the curtsy salute display. Females use a display that incites male courtship behavior, making a bobbing motion through the water as she holds her bill downwards.

Mating System: monogamous ; polygynandrous (promiscuous)

Red-breasted mergansers are relatively late breeders. Mated pairs arrive on the breeding grounds in May, egg-laying occurs in early June in the northernmost portions of the breeding range, with hatching in July and fledging in September to October. Females choose nests on land close to water, usually in dense vegetation or under objects, such as driftwood or boulders. Either an object or dense tree branches or grass forms a roof over the nest. Nests are usually within 23 m of the water, never more than 70 m. Females start the nest as a scrape, but gradually add grass and feathers as incubation progresses. They lay from 5 to 24 beige to gray eggs (mean 9.5), laying 1 egg every other day. They begin to incubate the eggs when the last egg is laid. Incubation is generally for 30 to 31 days, young hatch synchronously. Young fledge at 60 to 65 days after hatching. Because they breed relatively late, second clutches are unlikely. Most red-breasted mergansers mate first in their third year, although they are mature in their second year.

Breeding interval: Red-breasted mergansers breed once yearly.

Breeding season: Red-breasted mergansers breed in May and June.

Range eggs per season: 5 to 24.

Average eggs per season: 9.5.

Range time to hatching: 30 to 31 days.

Range fledging age: 60 to 65 days.

Range time to independence: 7 (high) weeks.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Average age at sexual or reproductive maturity (female): 3 years.

Range age at sexual or reproductive maturity (male): 2 to 3 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Females incubate the eggs and brood and care for the young until they abandon them within a few weeks after hatching. Males abandon females on the nest soon after she begins incubating the eggs.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Protecting: Female)

Clutch size: 6-16 (often 8-10); incubation: 29-35 days, by female; young first fly at estimated age of 59 days; first breeds at almost 2 years (Terres 1980, Palmer 1976).

Red-breasted mergansers have a wide distribution and large populations, they are not considered currently threatened. Some populations may be threatened by wetland destruction and contamination by pesticides and lead. They are also captured in fishing nets sometimes.

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

Red-breasted mergansers have a wide distribution and large populations, they are not considered currently threatened. However, some populations may be threatened by wetland destruction and contamination by pesticides and lead. They are also captured in fishing nets fairly frequently.

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

Winter visitor.

Canada

Rounded National Status Rank: N5B,N5N : N5B: Secure - Breeding, N5N: Secure - Nonbreeding

United States

Rounded National Status Rank: N5B,N5N : N5B: Secure - Breeding, N5N: Secure - Nonbreeding

Rounded Global Status Rank: G5 - Secure

Red-breasted mergansers are sometimes attracted to fish hatcheries and important salmon spawning streams. They are sometimes persecuted because of their predation on young salmon.

Negative Impacts: crop pest

Red-breasted mergansers are occasionally hunted, but they are not a common game bird.

Positive Impacts: food

Red-breasted mergansers are sometimes attracted to fish hatcheries and other commercial fish raising programs, as well as important salmon spawning streams. They are sometimes persecuted because of their predation on salmon parr (young salmon).

Negative Impacts: crop pest

Red-breasted mergansers are occasionally hunted, but they are not a common game bird.

Positive Impacts: food