Animal Diversity Web

Ge­o­graphic Range

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. (Tit­man, 1999)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• arctic ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native
• mediterranean sea
  • native

• Other Geographic Terms
• holarctic

Habi­tat

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. (Tit­man, 1999)

• 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

Phys­i­cal De­scrip­tion

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. (Tit­man, 1999)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger
• male more colorful

• Range mass

  800 to 1350 g

  28.19 to 47.58 oz

• Range length

  51 to 64 cm

  20.08 to 25.20 in

Re­pro­duc­tion

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. (Tit­man, 1999)

• 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. (Tit­man, 1999)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

• 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

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. (Tit­man, 1999)

• Parental Investment
• precocial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • protecting
    • female

Lifes­pan/Longevity

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. (Tit­man, 1999)

• Range lifespan
  Status: wild

  9.33 (high) years

Be­hav­ior

Red-breasted mer­gansers are mi­gra­tory, with dis­tinct breed­ing and win­ter­ing ranges. They are ac­tive dur­ing the day and are highly aquatic. They have rapid, ef­fi­cient flight and can swim and dive well by pro­pelling them­selves with their feet. Dives can be up to 44 sec­onds long and they can dive to depths of 9.2 me­ters. They can­not walk well be­cause their feet are so far back on the body. Red-breasted mer­gansers spend about 50% of their wak­ing hours in for­ag­ing ac­tiv­i­ties, al­though this varies with the avail­abil­ity of prey. They are highly so­cial and are typ­i­cally seen in groups, with the ex­cep­tion of breed­ing sea­son, when pairs sep­a­rate to mate and nest. They mi­grate in small groups of 5 to 15, but in their fall mi­gra­tion they may gather in large groups of up to 15,000. They do not de­fend ter­ri­to­ries, even dur­ing the breed­ing sea­son. Red-breasted mer­gansers also com­monly as­so­ci­ate with other birds, both in feed­ing and nest­ing areas. (Tit­man, 1999)

• Key Behaviors
• flies
• natatorial
• diurnal
• motile
• migratory
• social

Home Range

Red-breasted mer­gansers are gre­gar­i­ous and do not de­fend ter­ri­to­ries. Fe­males re­turn to nest in the area where they were hatched. (Tit­man, 1999)

Com­mu­ni­ca­tion and Per­cep­tion

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. (Tit­man, 1999)

• Communication Channels
• visual
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

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. (Tit­man, 1999)

• Primary Diet
• carnivore
  • piscivore

• Animal Foods
• amphibians
• fish
• eggs
• aquatic or marine worms
• aquatic crustaceans

Pre­da­tion

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. (Tit­man, 1999)

• Anti-predator Adaptations
• cryptic

• 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)

Ecosys­tem Roles

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. (Tit­man, 1999)

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). (Tit­man, 1999)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Red-breasted mer­gansers are oc­ca­sion­ally hunted, but they are not a com­mon game bird. (Tit­man, 1999)

• Positive Impacts
• food

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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). (Tit­man, 1999)

• Negative Impacts
• crop pest

Con­ser­va­tion Sta­tus

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. (Tit­man, 1999)

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  Protected

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

Mer­gus species, along with Lophodytes cu­cul­la­tus (hooded mer­gansers) are most closely re­lated to gold­eneyes (Bu­cephala) and smews (Mergel­lus al­bel­lus). (Tit­man, 1999)

Con­trib­u­tors

Tanya Dewey (au­thor), An­i­mal Di­ver­sity Web.

Ref­er­ences

Tit­man, R. 1999. Red-breasted mer­ganser (Mer­gus ser­ra­tor). The Birds of North Amer­ica On­line, 443: 1-20. Ac­cessed April 02, 2009 at http://​bna.​birds.​cornell.​edu/​bna/​species/​443.