species account

The Wood Duck (Aix sponsa) is the only native species of perching duck in North America. A member of the Anatidae family of ducks, geese, and swans, the "woody" sports sharp claws for gripping snags and clambering out of its tree-cavity nest.

The spectacular male's colorful, iridescent breeding plumage of whites, darks, and burgundies and his sleek crest are the explanation for the species name sponsa, which means "betrothed." In other words, he's dressed as if he's ready to be married. The female is cryptically colored, but can be identified easily by a teardrop-shaped white patch around the eye. The male's alternate, eclipse plumage is drab like the female's, but his bill retains its bright mix of colors in orange, black, and white.

In flight, the long square tail and light outer vanes of the primary flight feathers are distinctive. In one writer's words, the vanes look as if they have been sprayed with aluminum paint.

The Wood Duck has a diet similar to that of dabbling ducks like Mallard (Anas platyrhynchos) and Green-winged Teal (A. crecca): primarily invertebrates during the breeding season (especially among prelaying and egg-laying females) and predominantly plant life (especially duckweed) the rest of the year. Acorns and fruit are also taken.

The birds are intermediate in size between Mallards and teal: males weigh about 680 g and females about 460 g.

The most commonly-heard vocalization is the rising "hoo-eek" call given by the female.

Of the the bird's behavior, A. C. Bent writes in 1923:

No duck is so expert as the wood duck in threading its way through the interlacing branches of the forest, at which its skill has been compared with that of the passenger pigeon. I have stood on the shore of a woodland pond in the darkening twilight of a summer evening and watched these ducks come in to roost; on swift and silent wings they would glide like meteors through the tree tops, twisting, turning, and dodging, until it was almost too dark for me to see them.

Pair formation generally occurs in the fall, before southward migration in October and November. Come spring, the birds occupy two separate ranges: (a) in the west, from California to British Columbia, Montana, and Alberta; and (b) most of the territory east of the hundredth meridian from Texas to Florida and from Manitoba to the Maritimes. The breeding season begins anywhere from early March (in the southern end of the range) to early May (in the north). Most females return to the previous year's breeding ground, typically a wooded swamp.

While the male looks on, the female selects a cavity in a dead tree, with a 4-inch opening 3 to 60 feet off the ground. The cavity is sometimes a reused hole from a larger woodpecker; a man-made nest box of wood or plastic (lined with wood chips) may also be used. The nest is sometimes directly over water, but it may be as far as a mile away. Except for their own down, the birds add no additional material to the nest.

The hen lays a clutch of 8 to 10 fairly glossy, creamy-white, 2-inch long eggs (sometimes as few as 6 or as many as 15), at the rate of one per day. Once all of the eggs are laid, she alone begins a 28-32 day incubation.

The chicks hatch, downy and precocial, within hours of one another. (That is, they are not the naked, helpless, altricial nestlings typical of songbird species.) The next day, the female leaves the nest and gives soft "kuk kuk kuk" calls. In response, the chicks, already equipped with clawed feet, climb out of the cavity and drop to the ground below. The hen and the young immediately set out for water, which provides food and protection from land-based predators. Once on the water, ducklings face natural enemies like large pickerel, pike, and snapping turtles.

A. C. Bent writes that the young can climb out of a natural cavity three feet deep or more. He also gives anecdotal evidence that the hen carries the young from the nest, either in her bill or on her back -- such reports are now generally discredited.

Already somewhat independent at the age of 2 weeks, the ducklings can fly by 8 or 10 weeks. In warmer areas, in about 10% of the cases, the female will go on to produce a second brood.

Shortly after breeding, males begin to molt into "eclipse" plumage, a trait that Wood Ducks share with most other North American ducks. They exchange their bright nuptial colors for dull, cryptic ones, and they lose their fancy crests. The primary and secondary flight feathers are shed, and the drakes are flightless for about three weeks.

In August, the birds may disperse several hundred miles in all directions before September starts the courtship cycle again. As they migrate south, they retreat from Canada, the northern tier of the U.S., and the Appalachians; winter expands their range into Mexico.

On average, the birds return to breed for one season. Bellrose and Holm estimate the mean life span at 1.52 years, a bit more for males, and a bit less for females.

Like many Anatidae species, the Wood Duck is a non-obligate intraspecific brood parasite. That is, a female may lay some or all of her eggs in the nest of another Wood Duck, to be incubated by the other duck. "Dump-nest" clutches of up to 50 eggs can result. It may not be possible for the hen whose nest has been so parasitized (the host) to successfully incubate all the eggs, and thus some may not hatch.

There is evidence that dumping behavior increases as nests are more conspicuously placed and are spaced more closely together.

An interesting partial explanation for why intraspecific parasitism has evolved among duck species rests on the bird's site tenacity (philopatry) in its choice of nesting territory. Sisters or mothers and daughters tend to nest in the same area, and therefore may tend to parasitize one another. This would reduce the evolutionary cost of being parasitized, because the host would be brooding young that carry genes very similar to the host's. If hosts are indeed parasitized by close relatives, I might speculate that this behavior is similar to the cooperative nesting behavior shown by the Florida Scrub Jay (Aphelocoma coerulescens). Recent work by Semel and Sherman, however, indicates that wood ducks do not parasitize close relatives.

Due to over-hunting, the draining of wetlands, and forest fragmentation, the "bridal duck" was threatened with extinction at the start of the 20th century. In 1918, the federal government closed the hunting season for this bird for 23 years. A mid-century program showed that the species responds positively to artificial nest boxes, but the overall effect of nest boxes on population size is still not well understood. By the 1960s, the population had recovered to an estimated 3 million individuals.

Hepp and Bellrose cite the following priority topics for further research:

• establishing methods for estimating population size over large geographic areas, in order to evaluate the effects of habitat changes;
• identifying effects of forest management practices on natural tree cavity abundance;
• continuing long-term studies of marked Wood Ducks to learn about reproductive ecology and population biology.

Despite favorable population trends, the loss of suitable habitat, due to continued development and a growing human population, remains a concern: the fate of the Wood Duck, perhaps the most beautiful native North American duck, is far from secure.