A large, cosmopolitan family, collectively known as wildfowl, and all more or less bound to bodies of water. The family comprises two major groups: the swans and geese (subfamily Anserinae) and the ducks (subfamily Anatinae). There are also two other subfamilies: the whistling ducks (Dendrocygninae) and, in Australia, Freckled Duck, Stictonetta naevosa (Stictonettinae), which may be the sole survivor of a primitive group of wildfowl.
The largest and most majestic of the wildfowl are the swans. The four species found on the northern hemisphere are white, but the Australian Black Swan (Cygnus atratus) and South American Black-necked Swan (C. melancoryphus) are not.
The 'true geese', found only in the northern hemisphere, fall into two genera: 'gray geese' (Anser) and 'black geese' (Branta). Most species are highly migratory, many forming large, impressive flocks in winter.
Ducks are the most abundant and widespread wildfowl and comprise the largest and most varied subfamily, showing a high degree if adaptive evolution. Less terrestrial than swans and geese, they inhabit all kinds of fresh water and marine environments. The most familiar group is the dabbling ducks (Anatini), which includes Mallard (Anas platyrynchos), the ancestor of the 'farmyard duck'. Other groups include the shelgeese and shelducks, steamer ducks, perching ducks, torrent ducks, pochard ducks, eiders, sea ducks, and stiftails.
Swans and geese have a bill adapted for grazing on aquatic as well as ground vegetation: in both groups, the bill has lamellae in the form of serrated, horny 'teeth' along the edge of the maxilla.
Ducks can, broadly speaking, be divided into dabbling ducks and diving ducks. The former tend to be larger and bulkier, with a broad, flat, spatulate bill that also has lamellae. This feature is highly developed in shovelers, which feed on fine substances such as planktonic crustaceans. Diving ducks tend to be smaller and more compact, with a smaller, narrower bill adapted for eating both plant material and animal prey. The bill tends to be stronger and deeper in eiders and scoters, which feed chiefly on mollusks and crustaceans; in these species, the bill also has a swollen base housing salt-secreting nasal glands. In the sawbills and mergansers, which are mainly fish-eating ducks, the bill is long and narrow, again with serrated edges and even with a hooked tip adapted for holding onto prey. Some diving species, such as the goldeneyes (genus Bucephala) and, more particularly, the stifftails and Torrent ducks, have a long, beaverlike tail that may serve as a rudder. The perching ducks (Cairinini) are a highly diversified group that has a well-developed hind toe and strong sharp claws to assist climbing.
Most ducks have relatively short, pointed wings, and some of the smaller dabbling ducks, such as the teals, are highly maneuverable when they are flying. Of the less conventional species, steamer ducks are large and bulky, short-winged species, many of which are unable (or unwilling) to fly. Whistling ducks have a peculiar shape, with broad wings and long legs, and in flight look like long-necked and slightly hump-backed. Torrent duck (Merganetta armata) is a long-bodied, short-legged South American species whose streamlined shape is well adapted for swimming in fast-flowing Andes torrents. The peculiar Blue Duck (Hymenolaimus malacorhynchos) of New Zealand inhabits similar environments, with though claws for clinging to rocks.
For a short period in late summer, waterfowl molt their wing feathers and are temporarily flightless. During this time, male ducks molt into a subdued 'eclipse' plumage, which is either a much duller version of their 'full' plumage or is very similar to that of females. Eclipse plumage provides protective camouflage while the flightless males are vulnerable. Many species retain their male bill colors and, when regrown, their male wing patterns.
All species are essentially aquatic in summer, but some (swans, geese and wigeon) are much more terrestrial in winter, often grazing on agricultural land. At this time of year, geese in particular may be found in spectacular flocks sometimes numbering tens or even hundreds of thousands, usually roosting at night on large lakes or in sheltered coastal areas. Most other species are also gregarious outside of the breeding season, when large flocks may gather in areas with abundant food.
In spring in the northern hemisphere, wildfowl disperse or migrate, many to the tundra, others into the taiga zone or into mid-continental lakes and marshes that were frozen during winter. In fall, many species migrate south from these regions to winter in the closest ice-free areas. Many species of swans and geese migrate to traditional stop-over and wintering sites. Their migrations are not simply from north to south, but also to the southwest, southeast and even east to west. Milder coastal regions in temperate areas receive huge influxes, many of which start surprisingly early in mid- to late summer. Since wildfowl are flightless in late summer, many species undertake molt migrations to areas with a reliable and abundant food source.
Pair formation often occurs on the wintering grounds, with males usually following females back to their natal areas. Whereas swans and geese tend to mate for life and maintain strong family bonds year-round, ducks usually maintain only seasonal pair bonds.
Number of genera: 49
Number of species: 158
There are a number of subfamilies, but classifications can vary.
A list of all species can be found here.