BILL NAYLOR looks at the plethora of birds that make up the waterfowl family – from ducks to geese to swans
THE 147 TYPES of birds collectively known as waterfowl are instantly identifiable. They vary in size from the cotton pygmy teal (Nettapus coromandelianus), which weighs 160 grams and is only 26cm (10in) long, to the trumpeter swan (Cygnus buccinator), which can weigh as much as 17kg (371/2lb) and has a wingspan of 3m (10ft).
Of the seven species of swans, the South American Coscoroba swan (Coscoroba coscoroba) is thought to be a link between the swans and the 14 species of true geese. “Goose” is also the common name of a number of non-goose species such as the Egyptian goose (Alopochen aegyptiacus). Apart from the trumpeter swan, swans are not usually very vocal, unlike geese which have a rich vocabulary of calls. Female ducks usually have deeper voices than drakes and it’s the female who usually makes the quack call.
Male and female swans are called cob and pen. The equivalents in geese are gander and goose. Ducks are known as duck and drake, or alternatively duck can be a term for either sex.
Ducks are often divided into surface feeding and diving ducks. Surface-feeding ducks feed by dabbling – filtering the water with their specialised beaks. Surface-feeding ducks also feed on land on plants and insects, and in the case of the Mandarin duck (Aix galericulata), acorns.
The mallard (Anas platyrhynchos) is the best-known surface-feeder, and the ancestor of almost all domestic varieties of ducks. The two curly tail feathers of many domestic drakes is evidence of their wild mallard ancestor. Other surface-feeding ducks include the six feisty shelduck species, numerous teal species, and the 11 species of tree duck. Surface-feeders sometimes nest away from water in tree cavities.
Diving ducks have their leg set far back on the body, sit low in the water and have a lobed hind toe that propels them when diving. Most diving ducks have specialised bills. The tufted duck’s (Aythya fuligula) flattened bill rakes through gravel at the bottom of lakes and rivers for molluscs and insect larvae.
Eider (Somateria mollissima) use their strong bill to dislodge mussels on the sea floor. The African white-backed duck (Thalassornis leuconotus) feeds on bulbs of water lilies. The six mergansers (Mergus) including the stunningly beautiful smew (Mergus albellus) have serrated-edged beaks for seizing fish, and are often called “sawbills”. Other diving ducks include the exquisitely beautiful goldeneye, the pochards and stifftails (Oxyura), which include the infamous ruddy duck (O. jamaicensis). Diving ducks usually nest adjacent to the water in reeds and other cover.
Waterfowl have always been popular and well represented in aviculture, being among the first species of birds to be kept in captivity. They are generally easy to cater for and the majority readily breed. While many waterfowl are bred using incubators, parent-rearing should be undertaken whenever possible to retain natural parenting behaviour. Hand-reared geese are notorious for becoming imprinted and regarding themselves as human.
Not all waterfowl are easy to breed – pygmy geese, and sea ducks, including eiders and mergansers are particularly challenging. Waterfowl mainly mate on the water and anatids are among the few birds that possesses a true penis. Most waterfowl are monogamous, and some pair up for the breeding season. Others, such as tree ducks, geese and swans pair for life. Swans are particularly devoted and if a mate dies in captivity, they can easily pine to death.
Waterfowl hybridise more than any other group of birds, Hybrids are frequently found in the wild. Incubation is usually shared in the swans, geese and tree ducks. Among other ducks, the female usually incubates. The black-headed duck (Heteronetta atricapilla), also called the cuckoo duck, deposits its large eggs in the nests of Coscoroba swans, coots and even birds of prey!
Northern hemisphere ducks undergo an eclipse moult, and males assume plumage similar to the females. Southern hemisphere species don’t have an eclipse moult, and have less sexual dimorphism. In the paradise shelduck (Tadorna variegata) from New Zealand, for instance, the female is as colourful as the male. Ducks have to apply preen oil regularly to waterproof their feathers.
Parents have to waterproof ducklings to prevent them drowning. Ducks that are kept away from bathing water preen less and lose their waterproofing.
Although waterfowl are usually rendered flightless in captivity by clipping or pinioning, they are powerful flyers, and travel great distances sometimes at high altitudes. Bar-headed geese have been recorded flying over Mount Everest a height of 29,000 feet.
Some waterfowl such as ringed teal (Callonetta leucophrys) allowed to be fully winged remain in the vicinity of a waterfowl enclosure. Pygmy geese breed more easily when left fully winged in a roofed enclosure.
The closest living relatives of waterfowl are not coots, rails or flamingos as one might surmise, but the three species of screamers. Long-legged, heavily built birds with partially webbed feet and spurs on their wing. Outwardly they bear little resemblance to waterfowl. Anatomically, however, they are very similar and their family is classified within the waterfowl order Anseriformes.
Occupying another family is the unique Australian magpie goose. Unlike other waterfowl that lose all their flight feathers in an annual moult, the magpie goose moults its wing feathers alternately as other birds do. These geese also have a strong, obnoxious body odour, which can be detected from some distance. When parenting, the male magpie goose takes the lead role, incubates the eggs, and cares for the young, sometimes of more than one female.
■ Order: Anseriformes
■ Family Anhimidae Three species of screamers
■ Family Anseranatidae Magpie goose (Anseranas semipalmata)
■ Family Dendrocygnidae eight species of whistling ducks, plus white-backed duck (Thalassornis leuconotus)
■ Family Anatidae 137 species of swans, geese and ducks
Bill Naylor has extensive experience of waterfowl via his work in bird parks and zoos around the world.