Members of the family ANATIDAE (swans, geese and duck) have many common characteristics which distinguish them from other groups of birds. Most have short legs with webbed feet and their flight pattern is typically one of strong continuous wing beats with the long neck outstretched. This flight pattern helps the fowler to identify a flying bird as a wildfowl species while variations within the general pattern provide keys by which individual species can be recognised.
Plumage and Moulting
There are two quite distinct types of plumage characteristics to be found amongst swans, geese and duck. Most swans and geese, on the one hand, display almost identical plumage in both the males and the females of a species with the result that it is exceedingly difficult to tell the sex of an individual from the feather coloration alone. In contrast, the majority of duck species exhibit a degree of sexual dimorphism in their adult plumage so that the sexes may be fairly readily distinguished.
The males of dabbling duck such as mallard, teal, shoveler and pintail are brightly coloured, often with areas of iridescent plumage, but their females are relatively drab birds in feathers of mottled and spotted brown. This characteristic tends to be slightly less striking in the diving duck and even less so in the sea duck species but, nevertheless, it is not difficult to tell the sex of adult birds during the winter and spring.
One unusual but very important feature of the natural history of wildfowl is the manner in which they moult their plumage. Most other families of birds undergo a gradual moult during which the flight feathers are shed and replaced gradually over a protracted period. Wildfowl, on the other hand, moult all of their wing feathers simultaneously with the result that they become flightless for several weeks. The susceptibility of some male duck to predation during this flightless period is reduced by the fact that they typically moult out of their distinctive breeding colours and assume a drab appearance similar to the females and juveniles of their species. Other wildfowl, which do not exhibit markedly different eclipse plumage, may undertake moult migrations so that they spend the flightless weeks in places of comparative sanctuary.
Each species of duck or goose is also well adapted to its particular feeding habits. Dabbling duck are broad-billed and sieve water or mud to extract the small crustaceans or vegetable particles which form the staple part of their diet while geese and wigeon, being grazing birds, have shorter, more pointed bills. Those wildfowl which feed on land have strong, centrally placed legs well suited to walking whereas the diving duck are efficient swimmers by virtue of shorter legs situated farther towards the rear of their bodies. In addition to physical differences, wildfowl have also evolved behaviour patterns which reflect their feeding requirements. Many species, especially in winter, engage in flock feeding and some, such as the shoveler, appear to unconsciously co-operate by feeding in long lines so that one bird can sieve the water which has been disturbed by the feet of the duck in front.
In their breeding habits wildfowl also demonstrate a considerable degree of adaptation to their environment. Most duck species nest at ground level and, in consequence, they can suffer fairly high losses as a result of predation or flooding. Sitting duck may fall prey to foxes or feral mink while gulls and skuas are a threat to eggs and young ducklings. The survival of the species in such adverse conditions is assisted by the fact that duck lay fairly large clutches of eggs and the ducklings are able to walk and swim within a few hours of hatching.
Geese, being larger birds, are less susceptible to predation and tend to have a smaller brood size than most duck species. Both parents normally share in the protection of eggs and goslings. Young duck and geese grow at a rapid rate and those which breed in Arctic areas have to be fully fledged and ready to undertake an arduous migration by the end of the short northern summer. The timing of the breeding cycle is extremely important and there is evidence to suggest that day-length is the critical factor which stimulates behaviour so as to ensure that chicks hatch at a time of greatest food availability. This may be one of the reasons why wildfowl collectors in temperate countries have difficulty in breeding some of the species which spend the summer in the high Arctic.