By J. Dale James, Ph.D.
In the world of waterfowl, species are taxonomically classified based on their physical characteristics and behaviors. There are some species, however, that have similar habits and habitat preferences, yet are not closely related genetically. Two prime examples are wood ducks and black-bellied whistling ducks. Let's take a closer look at these fascinating waterfowl species, their similarities and differences, and why these birds are now sharing many of the same habitats across the southeastern United States.
The magnificent wood duck has captivated humans throughout history. Images of wood ducks were featured prominently on Native American artifacts dating back centuries. In the 1835 edition of his book Ornithological Biography, John James Audubon wrote, "At this moment, when my heart is filled with delight, the rustling of wings comes sweeping through the woods, and anon there shoots overhead a flock of Wood Ducks." Later, Henry David Thoreau wrote of the wood duck, "What an ornament to a river to see that glowing gem floating in contact with its waters!"
The wood duck is the only North American member of the "perching duck" tribe, although some authorities now include the species with dabbling ducks. Like other members of the perching group, wood ducks have long toes with claws, which gives them the ability to perch in trees. They also prefer wooded and scrub-shrub wetlands and nest in tree cavities. Among the adaptations that are somewhat unique to wood ducks is their round body shape, which makes them more buoyant than other ducks and allows them to sit higher on the water. They also have broad wings and a long tail, features that allow them to maneuver nimbly through trees in forested habitats.
Black-bellied whistling ducks are often referred to as "tree ducks" because they inhabit forested wetlands and commonly perch in trees. Until recently, these striking birds were found only in Mexico and South Texas, but now appear to be expanding their range across the southeastern United States. Like wood ducks, black-bellied whistling ducks nest in tree cavities and will also use manmade nest boxes. This behavior likely developed over time to counter high predation rates and unpredictable and changing water levels in backwater wetlands and riverine floodplains. Wood ducks and black-bellied whistling ducks are the only North American waterfowl species known to successfully produce two broods in the same breeding season. This is possible in southern latitudes due to the balmy climate, which provides for a longer breeding season.
The migration habits of wood ducks and black-bellied whistling ducks are also similar. Wood ducks that breed across northern portions of their range are migratory, while those raised in the Deep South tend to live in the same areas year-round. Black-bellied whistling ducks are considered to be migratory only in the extreme northern limits of their range, but are known to make shorter regional movements in other areas.
Despite these similarities, black-bellied whistling ducks and wood ducks are different in many ways. In fact, black-bellied whistling ducks are more similar to geese and swans than they are to ducks. They belong to the genus Dendrocygna, which roughly translates to "tree swan." Like geese and swans, whistling ducks are monomorphic (hens and drakes look similar) and form long-term pair bonds.
Black-bellied whistling ducks, which once had a limited U.S. range, have been "spreading their wings" in recent years. Breeding populations now exist across the southeastern United States, and wayward individuals have been sighted as far north as Nova Scotia and North Dakota. As black-bellied whistling duck populations continue to grow, additional research will be needed to better understand the life history of this species, including its interactions with wood ducks and the potential for nest site competition and nest parasitism between the two species.
While the wood duck and black-bellied whistling duck are both beautiful and unique birds, they are just two of the many waterfowl species found across North America. Waterfowl biologists and managers must provide a wide variety of habitats across vast landscapes to meet the life-cycle needs of this remarkably diverse group of birds. Ducks Unlimited and its partners deliver comprehensive conservation programs and support science and public policy work that contribute to the sustainability of our continental waterfowl populations and their habitats. Through the dedicated efforts of our supporters and staff, DU will continue to lead efforts to ensure a bright future for wood ducks, black-bellied whistling ducks, and other waterfowl across North America.
Dr. Dale James is director of conservation planning in DU's Southern Region.