Understanding Waterfowl: Wood Ducks East to West

By J. Brian Davis, PhD, and John M. Eadie, PhD

Revered for its spectacular plumage, amazing flying abilities, and fine qualities as table fare, the wood duck (Aix sponsa) is one of six cavity-nesting duck species in North America and the only member of its genus in the western hemisphere. At the turn of the 20th century, wood ducks were driven to the brink of extinction by market hunting and widespread loss of bottomland hardwood forests and other important habitats. Protections granted by the Migratory Bird Treaty Act of 1918 and the restoration of crucial habitats helped wood ducks achieve a dramatic recovery over the following decades, and populations of these highly prized birds are now healthy.

You can find wood ducks in southern Canada, across the continental United States, and at least as far south as Cuba. Biologists regard wood ducks as “forest adapted,” and that is generally true. The bottomland hardwood forests and swamps of the Mississippi Alluvial Valley, for example, are legendary wood duck habitats. Despite widespread habitat losses in this region, scattered tracts of bottomland hardwood forest and swamp host large numbers of migrating and wintering wood ducks and support significant populations during the breeding season. In the Midwest and Atlantic states, wood ducks occur in a variety of habitats, including slow-moving rivers and streams, swamps, beaver ponds, and emergent wetlands in forested areas. 

The largest population of wood ducks in the West exists in the Central Valley of California. Prior to European settlement, the valley consisted of vast expanses of grassland, bulrush (tule) marshes, vernal pools, and tracts of riparian forest along waterways. The region is largely bereft of large contiguous tracts of lowland timber, which typically provide most of the tree-cavity nesting sites used by wood ducks. The highest densities of nesting wood ducks in the Central Valley occur in the 18,000-acre Butte Sink in the northern Sacramento Valley. In other parts of the West, such as western Washington and southern British Columbia, as well as the Willamette Valley and Columbia River in Oregon, woodies are found in pockets of forested lowlands and along rivers, ponds, and wetlands with large cottonwood groves.

How can wood ducks thrive in such remarkably diverse habitats? The legendary Dr. Frank C. Bellrose, the father of wood duck biology and conservation, eloquently reasoned that “California has more potential to raise wood ducks than about anywhere else.” When queried about the lack of bottomland forest and swamps, he simply smiled and said, “You have a Mediterranean climate and water, which means insects—now all you need are the holes for nesting.” He was absolutely right. Wood duck box programs in the Central Valley and other western regions have been very successful in boosting populations.

Nesting Ecology

Most female woodies lay an average of 10 to 12 eggs in each nesting attempt, but some hens find themselves responsible for incubating “supernormal” clutches that contain far more eggs. These enlarged clutches arise from a social behavior called brood parasitism, in which one or more females lay eggs in the nests of “host” females, who incubate these eggs together with their own. It is not uncommon for some nests to contain dozens of eggs. In fact, we have recorded 72 eggs in one nest and 32 ducklings hatched from a clutch of 35 eggs.

Recent studies have revealed that a single nest box can attract up to 20 different females. Some females visit 30 or more nest sites, potentially laying eggs in many of them. Even more remarkable, some female wood ducks will successfully hatch and rear one batch of ducklings and then nest again, producing two broods during a single breeding season. Although the incidence of double-brooding is low—perhaps involving only 3 to 10 percent of breeding females—this behavior is not accidental. The exceptional reproductive activity of these wood ducks is possible thanks to longer nesting seasons in those portions of their range that have mild, wet winters and springs and an abundance of tree cavities in which to nest.

Wood Duck Management

Wood ducks are obligate secondary cavity nesters. This means that they cannot make tree cavities themselves. Instead, they must rely on other species, often woodpeckers, or tree rot to create nest sites. Consequently, the clearing of mature forests and the corresponding loss of nesting cavities during the late 19th and early 20th centuries devastated wood duck populations. To help provide surrogate nesting sites for the birds, Bellrose and his colleague Art Hawkins pioneered the use of nest boxes, which were readily accepted by the birds and are now a central component of virtually all wood duck management plans.

How much do nest boxes boost wood duck production? Once again, differences exist between eastern and western populations. The regrowth of bottomland hardwood forests in the East has provided more natural nest cavities in many areas. Bellrose estimated that 90 percent of wood duck production came from natural cavities. Nevertheless, the capacity for nest boxes to establish new wood duck populations or greatly enhance local populations is well recognized. Wood ducks quickly find and use nest boxes when they are placed in suitable habitat. If the boxes are properly maintained, the hens that use them can produce large numbers of ducklings. This is especially true in the West, where nest box programs in some regions have achieved almost unbelievable results. In California, for example, a large, well-coordinated nest box program produced over 1 million wood duck ducklings from 1991 to 2024.

Other Limiting Factors

Nest sites are not the only limiting factor influencing wood duck populations. Adult survival also has an impact. Females can breed at one year of age, and it is believed that most attempt to nest each year. Annual survival of females in the East ranges from 59 percent in the South to 46 percent in the North, with younger females having lower survival than adults.

Female survival appears to be similar among eastern and western populations. However, wood duck harvests differ substantially in these regions. An average of just over 975,000 woodies were harvested annually across the United States from 2019 to 2022. The Mississippi Flyway accounts for 50 to 60 percent of the total US harvest. Far fewer wood ducks are harvested in the Pacific Flyway, where only about 40,000 are bagged each season, with 55 percent of the total taken in California.

Perhaps the single most important limiting factor influencing wood duck populations, both East and West, is duckling survival. In Mississippi and Alabama, for example, radio telemetry studies indicate that individual duckling survival can range from 15 to 29 percent. Similarly low duckling survival (12.5 percent) was recorded in California. Predation was the major cause in most locations, pointing to the need for high-quality brood habitat consisting of wetlands with good cover, abundant invertebrate food resources, and reliable water supplies.

Wood ducks are a remarkable conservation success story, and their unique behavior, sheer beauty, and many sporting qualities are all worthy of celebration. Wood duck nest box programs are a success story in themselves, not only for producing more woodies, but also for demonstrating how waterfowlers and other conservationists can roll up their sleeves and give back to these beautiful birds, fostering a shared conservation ethic that unites us all.

Status of Wood Duck Populations

After decades of these monitoring efforts, the best population estimate for breeding wood ducks in the Central, Mississippi, and Atlantic Flyways is just under 3 million birds. The Pacific Flyway population is much smaller, totaling about 90,000 breeding wood ducks—or roughly 2 to 3 percent of the continental breeding population. Interestingly, several studies have discovered that wood duck populations in the West differ genetically from those in the East, suggesting that there has been little genetic exchange between these populations, at least historically.

Dr. Brian Davis is the James C. Kennedy endowed professor in Waterfowl and Wetlands Conservation in the Department of Wildlife, Fisheries and Aquaculture, Mississippi State University. Dr. John Eadie is a distinguished professor emeritus and the Dennis G. Raveling endowed chair emeritus in Waterfowl Biology in the Department of Wildlife, Fish and Conservation Biology, University of California, Davis.