Physical Characteristics
Ducks are placed in the avian order Anseriformes along with the screamers, swans, and geese. The long-legged screamers lack webbed feet and are placed in their own family, the Anhimidae. The ducks, geese, and swans are gathered in the family Anatidae and are collectively called waterfowl. The anatids are united in having webbed feet, a boat-shaped body, a dense covering of feathers, and a broad and somewhat flattened bill that is variously modified for straining minute surface organisms, gathering shellfish, grazing on aquatic plants, or catching fish. Ducks differ from swans and geese in several ways. They are generally smaller and have shorter necks and legs, which are set well back on the body. They are good swimmers but walk with a peculiar waddling gait on land. Ducks are also distinguished in having scutellate (overlapping) scales on the front of their legs, while geese and swans have netlike or reticulate scaling. Unlike their larger kin, ducks have two molts each year. The first molt occurs after breeding in males and shortly later in females. During this molt, ducks shed their flight feathers and males trade their bright breeding plumage for the plain plumage colors similar to those of females, called an eclipse plumage or hiding plumage. The plain colors of the eclipse plumage camouflages the flightless birds until their new flight feathers grow. The second molt occurs in late summer or early fall and produces the bright breeding plumage of males in preparation for courtship on their wintering grounds. Ecologically, all ducks are birds of aquatic habitats that reach their greatest abundance in the innumerable ponds, shallow lakes, and marshes of the world. Several species are sea ducks that frequent shore habitats, estuaries, and coastal marshes during the nonbreeding season.
Courtship and Nesting
Courtship and pair formation occurs on wintering grounds as males and females engage in speciesspecific displays. Males of many species perform intricate head and tail jerks that "point" to the bright metallic colors of their wing speculum. Many sea ducks add a courtship finale by flicking water spurts with their head or feet, all the while bowing and cooing. The stiff-tailed ducks of the tribe Oxurinae twist their heads far over their backs, then violently thump their bills against the inflated necks, uttering a stream of bubbles and a series of burps. Following courtship the female builds a nest of reeds, sedges, and grasses in marshes or along the shallow, weed-choked margins of lakes and ponds. The mergansers and wood ducks nest in cavities in trees, while shelducks are unique in selecting burrows in which to lay their eggs. In most species, the female alone builds the nest of nearby materials and lines it with downy feathers plucked fromher breast. The down feathers provide wonderful insulation for the eggs and are arranged in layers over the eggs for protection from predators when the female leaves the nest to find food. Most ducks lay relatively large clutches of eight to twelve smooth, white eggs. A few species, such as the black-headed duck (Heteronetta atricapilla) of South America, are brood parasites that lay their eggs in nests of other ducks, coots, and ibis. Incubation begins when the clutch is complete, ensuring that all of the young hatch at the same time. Incubation takes about a month (twentytwo to forty-one days). The precocial young are densely covered in a fluffy coat of down feathers. In most species, the young abandon the nest shortly after hatching to accompany the female, who leads them to nearby feeding grounds. The young instinctively feed themselves under the watchful eye of the female, who marshals them to safety in the weeds if danger threatens. Predation often decimates the young of a nest, as snapping turtles, fish, foxes, coyotes, hawks, and owls are quick to snap up the defenseless young. Those that survive fledge in about a month and may remain in the company for several more weeks. In some species, the young accompany the female on the southward migration, but most young migrate on their own, relying on inbuilt genetic programming to fly hundreds and sometimes thousands of miles using the sun or stars or both as navigation aids. Many species memorize landmarks such as lakes and river courses, which supplement celestial navigation aids on future migrations. Studies have also suggested that at least some ducks are able to tap into the earth's magnetic field for directional aid on overcast days, when other cues are unavailable.
Duck Tribes: Anatini
The ducks are subdivided into several tribes on the basis of anatomical and behavior differences. Several tribes contain forms intermediate between ducks and their near relatives, the geese. The familiar puddle ducks of ponds and marshes belong to the tribe Anatini. They are called tippers or dabblers because of their habit of tipping up to feed in shallow waters of ponds, marshes, and rivers. The dabblers have feet set farther forward on their bodies than other ducks and bound into the air when taking flight. Males of this group usually have a brightly colored, iri- Ducks • 389 descent wing patch or speculum and are often brightly colored about the head and neck, while females are drab colored. There are about forty-one species of dabbling ducks worldwide, of which ten breed in North America. Some typical dabblers include the teal, widgeons, pintails, gadwalls, and shovelers. The best-known dabbler is the mallard, which occurs in both wild and domesticated forms. Most of the domestic species, such as the barnyard duck and Indian duck, are probable descendants of the mallard. Dabbling ducks are surface or shallow water feeders of creeks, ponds, and marshes. Some strain food from soft mud, others feed on the water surface, and still other species tip up and then stretch their necks down into the water, taking food from submerged vegetation or feeding on the vegetation itself. Food consists of the leaves, roots, tubers, and seeds of floating or submerged vegetation and a wide variety of small animals, mostly shrimp, scuds, shellfish, and insects. Long-necked dabblers like the northern pintail (Anas acuter) tip up to feed directly on the bottom. Smaller species such as teals feed in shallower waters or on mudflats. The broad, spatulate bill of the northern shoveler (Anas clypeata) strains minute organisms fromthe water surface. Dabblers are found on all continents, but they are especially plentiful along interior ponds, marshes, and creeks. In most dabblers, the male is jealously attentive to the female during courtship but deserts her shortly after the eggs are laid, leaving her to defend the nest and raise the young entirely on her own. She builds a crude nest of grasses and weeds lined with down from her breast. After abandoning the female, the male may seek another female to repeat the performance. If none is available, they spend the rest of the breeding season loafing and hiding while in the eclipse plumage. After their second molt, the males sport bright new feathers to enter the winter months, during which courtship and pair formation for the following breeding season takes place.
Aythyinae, Mergini, Cairini, and Oxyurinii
The pochards (redheads), canvasback (Aythya valisineria), and scaups belong to the tribe Aythyinae, which are called sea ducks or bay ducks. They frequent coastal locations in winter but build a floating nest among the reeds and grasses of interior lakes, rivers and marshes. Most diving ducks have short tails and wings, but large paddle feet with a distinctive, paddlelike flap on the hind toe for diving. They feed mostly on underwater plants and animals. If danger threatens, diving ducks submerge and can swim underwater for long distances. They take flight by skittering along the top of the water. Because they have short wings on large bodies, most bay ducks fly 390 • Ducks The mallard duck is a common sight on the ponds and lakes of North America. (Digital Stock) with rapid wing beats and always appear in a hurry in flight. The tribe Mergini includes a varied mix of mergansers, scoters, eiders, goldeneyes, and the spectacularly colored harlequin (Histrionicus histrionicus) and oldsquaw (Clangula hyemalis). Mergansers are powerful divers that pursue fish underwater, catching and holding them with their narrow, serrated bill. They nest in cavities in trees or in rock crevices along rivers and streams, as do the goldeneyes of this tribe. The tribe also includes eiders, which nest in the circumpolar Arctic tundra. Eiders are the source of eiderdown, which the female plucks from her breast to line the nest and insulate the eggs and young. The most striking of the Mergini is the harlequin duck, with its patchwork quilt of chestnut, blue, and white plumage. Harlequins feed in cold, fast-flowing Arctic streams. Members of the tribe Cairini have long legs and sharp claws which enable them to clamber about branches and limbs. Called wood ducks or tree ducks, they include the gorgeously colored wood duck (Aix sponsa) of North America and mandarin duck (Aix galericulata) of southeast Asia. This tribe also includes the drab muscovy (Cairina moschata), which occurs widely in both wild and domesticated forms. Unlike other tribes, the wood ducks frequent the gallery forests of rivers and lakes, forested swamps, and woodland pools. They typically nest in tree cavities just adjacent to water. When old enough, the downy young half tumble and half jump into the water below the nest cavity. The ruddy duck (Oxyura jamaicensis) exemplifies the tribe of stifftails called Oxyurinii. These dumpy little ducks are predominantly reddish or brownish in color and have upright tails for which they are named. Except for teals, the stifftails are small ducks that are noted for laying exceptionally large eggs for their body size. For example, the female ruddy duck, although scarcely weighing a pound herself, lays a clutch of fourteen eggs, weighing a total of nearly three pounds, with each egg averaging over 2.5 by 1.75 inches in length and width.
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