Life history
Hatchlings emerge from the egg with a complete covering of down and can take to the water as soon as they leave the nest, within 24 to 48 hours. They can forage for themselves, but at least one parent remains with them, guarding, guiding, and, initially, brooding them at night and during inclement weather.
The downy plumage is retained for from two weeks (small ducks) to six weeks (large swans) and is then replaced gradually by the feathers of the juvenal plumage. The flight feathers, the last to develop, likewise vary in their rate of growth, taking from five weeks to five months. At fledging, young ducks must make their own way on migration. In species breeding in the far north, this begins in early autumn. Young geese and swans, on the other hand, remain with their parents during their first winter and migrate to and from the wintering grounds in their company. In most large species the juvenal plumage is retained through much of the first year of life. Ducks, however, begin to lose the juvenal body feathers almost at once. Some replace the juvenal plumage with an immature nonbreeding (or “basic”) plumage, acquiring the first nuptial (or “alternate”) plumage in the second autumn. Other species molt directly from juvenal to nuptial and are practically indistinguishable from adults in plumage and size at the age of six months. Swans and geese do not reach full size until the end of their second year, and even at that age swans still retain some immature feathers.
In migratory species social flocking and pair formation occur on the wintering grounds, followed by the return migration to the breeding grounds. In the high Arctic regions the birds arrive ready to nest as soon as the snow cover melts and the water opens; in lower latitudes the process is more leisurely. When the female duck begins to incubate, the male generally deserts her and joins forces with other males, often after making a molt-migration to another area some distance from the breeding site. The nuptial plumage is lost, and a dull “eclipse” plumage, rather femalelike, is assumed before the simultaneous molt of the flight feathers. The resulting flightless condition lasts three or four weeks, during which the birds skulk in thick cover or remain on large bodies of water. In female ducks this wing molt is delayed until after the young have fledged. The eclipse plumage is succeeded in three to six months by the next nuptial plumage. In the case of swans and geese the male remains and molts with the female and family; immature birds and unsuccessful breeders may, however, make a molt-migration to a separate area.
The foregoing life cycles are typical of waterfowl breeding in north temperate or Arctic regions. In the tropics and south temperate regions, migration of waterfowl may not be necessary. When it does occur, migration may be in response to ecological factors such as the onset of the rainy season. Males and females tend to be similar in plumage and to lack eclipse plumages. The birds are ready to breed at any time that conditions are favourable. Undoubtedly there is a relationship between hormonal balance and the appearance or absence of eclipse or brightly coloured plumages, but the exact mechanism is not yet known.
The mature anseriform has a potentially long life, though this is seldom achieved in the wild. In captivity ducks have lived for 20 years, geese and swans for more than 30; there are reports of geese exceeding 40 years of age and swans, 50. Wild populations suffer heavy losses (up to 70 percent) among first-year birds. The adults then experience annual mortalities of 10 to 50 percent, depending on the extent of hunting and on natural factors. At the higher end of this scale the population is almost completely replaced within three years. With luck and cunning an occasional bird may survive for 15 to 20 years or more.