By J. Brian Davis, Ph.D.
The survival and recovery of wood duck populations in North America are renowned wildlife success stories. By the late 1800s to early 1900s, extinction of the wood duck seemed imminent. Sentiments like, “Becoming scarce, likely to be exterminated,” and “Almost exterminated, only few breed” reverberated among ornithologists in eastern portions of the continent.
Destruction of bottomland hardwood forests—the bird’s primary breeding and wintering habitat—and market hunting were the two major factors that contributed to the species’ decline. Because of their extensive breeding ranges in eastern North America, where most people lived in the early 20th century, wood ducks were probably the most hunted waterfowl species prior to 1918. Wood ducks were hunted from September to April. In 1918, however, the Migratory Bird Treaty Act prohibited the hunting of wood ducks nationwide. Wood duck populations recovered, and seasons were reopened in 1941. Fortunately, some lowland habitats composed of impenetrable vegetation and subject to prolonged flooding withstood man’s environmental barrage, providing safe havens for wood ducks in parts of their range. These areas provided the remaining wood duck population that eventually expanded into its current range in North America.
Population Surveys and Management
Each spring and summer in selected parts of Canada and the United States, biologists fly airplanes along transects encompassing millions of acres, enumerating the numbers of May ponds, breeding pairs of ducks, and numbers of duck broods. These counts help estimate the population sizes of nesting ducks and are used to formulate waterfowl hunting season frameworks and daily bag limits.
Estimating the population size of wood ducks from aircraft, however, is basically impossible because the birds prefer to nest in forested wetlands and other densely vegetated habitats. Counts have even been attempted from helicopters, but to little avail. Thus, biologists primarily rely on four techniques to monitor wood duck populations and other biological trends of the species: 1) the annual Breeding Bird Survey (BBS), 2) long-term monitoring of wood duck nest boxes, 3) examining wings of harvested birds at annual Wing Bees, and 4) hunter harvest surveys and recoveries of wood duck bands.
The BBS is a roadside survey conducted annually in June to estimate the relative abundance of breeding birds across Canada and the United States. Monitoring nest boxes across large geographic areas, such as statewide or by flyways, allows biologists to monitor nesting attempts and the nesting success of breeding wood ducks. This information is useful for biologists to assess long-term trends in nesting success and the general health of local wood duck populations.
The annual Wing Bee is a meeting where biologists examine the wings of ducks harvested by hunters to determine the species, sex, and age of the birds. This technique allows biologists to estimate the ratio of the numbers of young to adults in the population as an index to productivity. Lastly, bands from harvested wood ducks reported by hunters to the U.S. Fish and Wildlife Service provide critical information, such as the age, sex, and location of a bird when it was harvested. These data are vital to estimating waterfowl species’ annual survival rates and other important population trends.