Northern Prairie Wildlife Research Center
Wood ducks were very abundant when the European settlers first arrived in this country. However by 1900, the combination of deforestation and unregulated hunting brought wood ducks to the brink of extinction. Today, the wood duck population is thriving in North America, in part because hunting is regulated but more importantly because forests have begun to recover from earlier logging. Additionally, concerned conservationists have erected tens of thousands of nest boxes in the past 50 years to aid nesting wood ducks.
Wood duck pairs begin arriving in Iowa from mid March to early April. Because they are not territorial, many wood ducks can share areas of good habitat. Hens feed on invertebrates (insect larvae and snails) in the shallow ponds or backwaters (less than one foot deep) that warm up first in the spring. Invertebrates provide the protein and calcium necessary for egg production.
Wood ducks naturally nest in tree cavities. Mature forests may have as many as 3 suitable cavities per acre. Black willow, basswood, soft maple, cottonwood and some oaks contain most of the suitable cavities. Suitable cavities most often are located in living trees, are relatively close to water, are 10 to 20 inches deep, are 8 to 12 inches wide, and have 3 1/2 to 5-inch diameter entrance holes. Cavities from 2 to 65 feet above the ground have been used successfully.
Most wood ducks nest when 1 year old. Hens usually begin nesting in late March in southern Iowa and mid April in the north. Hens lay one 2-inch long dull white or cream-colored egg per day. Average clutch size is 12, but completed clutches range from 1 to 20 eggs. Clutches with more than 15 eggs are often "dump nests" (a nest in which more than one hen has laid eggs). Dump nesting is most common where breeding populations are high. Hens incubate the eggs for an average of 30 days. About 30 percent of the wood duck clutches laid in natural cavities hatch. Many nests are destroyed by predators (raccoons, snakes, squirrels) or are abandoned. When a nest is destroyed, the hen usually attempts to nest again. She may make repeated attempts to hatch a clutch, even into July.
Within 24 hours after hatching, the hen calls her young from the nest. The ducklings scramble up the side of the cavity and, although they cannot fly, fearlessly leap to the ground or water below where they land unhurt. Since wood ducks may nest a mile or more from water, hens must often lead their broods over land to nearby wetlands.
Preferred brood rearing wetlands have high numbers of aquatic insects for the ducklings to eat and emergent vegetation (cattails, bulrushes, willows, buttonbush) for escape cover from predators. The family may move overland several times to find wetlands with suitable food and cover. Ducklings attain flight when 8 to 10 weeks old. About half the brood survives to flight stage.
Drakes leave their hens during incubation and gather in flocks, often migrating to large marshes to molt. Hens begin molting on brood rearing wetlands after the young can fly. Adult wood ducks are flightless for 4 to 5 weeks while growing new flight feathers. Family groups do not stay together during migration and hens find new mates by the next spring.
Hens that nest successfully, and their female offspring, often return to the same area, and even the same box or cavity, to nest the following year. This homing instinct makes it possible to build a population of wood ducks that use a particular wetland or group of nest structures.
Although many different nest structures have been tried, experience has shown that wood ducks prefer the basic box structure or designs with similar dimensions. The following are tried and true designs for wood duck houses.
Unlike most of the mallard or goose nesting structures, wood duck boxes are also used by other ducks such as hooded mergansers, goldeneyes and buffleheads. In addition, squirrels, starlings, swallows, owls, kestrels and woodpeckers, often compete with hen wood ducks for these nest sites. Raccoons, opossums, and snakes not only compete for use of the boxes, but may also eat the eggs and/or kill the hens. It is critical to erect boxes properly, with predator guards if necessary, so that they don't become death traps for the nesting hens. Annual maintenance is the key to consistent, successful use.