the red-breasted merganser (mergus serrator) is a diving duck , one of the sawbills .
the genus name is a latin word used by pliny and other roman authors to refer to an unspecified waterbird , and serrator is a sawyer from latin serra , "saw" .
the adult red-breasted merganser is 5162 cm (2024 in) long with a 7086 cm (2834 in) wingspan .
it has a spiky crest and long thin red bill with serrated edges .
the male has a dark head with a green sheen , a white neck with a rusty breast , a black back , and white underparts .
adult females have a rusty head and a greyish body .
the juvenile is like the female , but lacks the white collar and has a smaller white wing patch .
the call of the female is a rasping prrak prrak , while the male gives a feeble hiccup-and-sneeze display call .
it has been claimed to be the fastest bird in level flight , reaching speeds of 161 km/h (100 mph), but is disputed whether the white-throated needletail is faster , reportedly flying at 170 km/h (105 mph) .
red-breasted mergansers dive and swim underwater .
they mainly eat small fish , but also aquatic insects , crustaceans , and frogs .
its breeding habitat is freshwater lakes and rivers across northern north america , greenland , europe , and asia .
it nests in sheltered locations on the ground near water .
it is migratory and many northern breeders winter in coastal waters further south .
the red-breasted merganser is one of the species to which the agreement on the conservation of african-eurasian migratory waterbirds (aewa) applies .
