Wood ducks nest seasonally in forested areas across North America from coast to coast in southern Canada and the northern tier of states. From southern British Columbia, a narrow strip of breeding range extends northward along the coast through Southeast Alaska. We see them here in Juneau fairly commonly. They nest in several places in the Mendenhall Valley, for instance. These western breeders migrate south for the winter, flying at night; many of them go to the Central Valley of California. They are often year-round residents in most of the eastern U.S., Cuba, parts of the Pacific Northwest, and California.
They are cavity-nesters, using tree cavities and nest boxes. Suitable tree cavities are often found in old, large, mature trees with broken branches that have heart rot. Deforestation of old-growth probably reduced the availability of good nest sites and drainage programs brought loss of suitable wetland habitat. Furthermore, wood ducks were overhunted in times past. However, they seem to have made a good recovery, in part because hunting is better regulated, and also conservation-minded folks have installed nest boxes in many places. Much of what we know about their nesting biology comes from research on nest box breeders.
Females choose the nest site while accompanied by their attentive mate. Most nests are placed fairly close to water, although some nests have been found over a kilometer away from any water. The female lines the chosen nest site with down feathers from her body. Wood duck males are quite faithful during the formation of a clutch, but males may mate with other females when the first clutch is completed. Clutch size averages about 10 to 12 eggs, with lots of variation. One egg is laid per day, typically, and the male attends to the female when she comes to the cavity to lay the egg of the day. The female begins incubation a few days before the clutch is completed, so hatching is not completely synchronous. The incubation period is roughly four weeks, sometimes longer, depending in part on ambient temperatures. Ducklings are downy and able to walk and feed independently. They usually leave the nest on the morning after hatching, being called by the female waiting below, and can survive a long jump down from the nest opening to the ground. After leaving the nest, the brood stays with the female for several weeks. Survival from hatching time until they can fly is commonly around 50%. There is no male parental care.
Brood parasitism is reported to be quite high (in some cases over 50%), either by other female wood ducks or mergansers, and perhaps other cavity-nesting ducks. Many animals prey on eggs and incubating females; in the east and south, raccoons and rat snakes often top the list (no info for SEAK).
The scientific name is Aix sponsa. Aix is a Greek word for waterfowl; “sponsa” means “bride” — in this case, referring to the fancy dress of the male. There is one other species in the genus: the mandarin duck, which is native to the eastern Palearctic but has been introduced to other parts of the world.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
