By Mike Brasher, Ph.D.
The roughly 150 species of ducks, geese and swans that occur around the world display an amazing variety of physical features and behaviors. Across this array of waterfowl, some species are more closely related than others. Scientists use behavior, anatomy and sophisticated genetic analyses to classify related birds into groups that reflect these relationships. For example, essentially all dabbling ducks belong to the genus Anas, while diving ducks belong to the genus Aythya.
But even within the same genus, scientists can identify subgroups that possess greater degrees of ancestral relatedness. The "blue-winged ducks" are a prime example. This group includes three North American species—northern shovelers, blue-winged teal and cinnamon teal—as well as four species found in other parts of the world.
Waterfowlers and other bird enthusiasts have likely noticed the similar, striking blue wing patches on northern shovelers and blue-winged teal. Their close relative, the cinnamon teal, also has similar wing markings, but is less widely known because of its small population size and limited range, which is largely confined to the Pacific Flyway. Closer inspection of the life histories of these species reveals amazing similarities beyond physical appearance.
Blue-Winged Ducks of the World Seven "blue-winged ducks" occur worldwide, with at least one on every continent except Antarctica. This group includes three small-bodied teal (blue-winged teal, cinnamon teal and garganey) and four shovelers (northern shoveler, cape shoveler, red shoveler and Australasian shoveler).
The northern shoveler is the most widely distributed of these ducks, occurring throughout North America, Europe and Asia. Its southern relative, the cape shoveler, is the most restricted, occurring only in South Africa. The Australasian shoveler, as you can probably guess, is found in Australia and New Zealand. And if you are ever lucky enough to see a male Australasian shoveler in breeding plumage, with its spoon-shaped bill, iridescent green and slate blue head, rusty flanks and white facial crescent, there will be no denying its relationship to our blue-winged teal and northern shoveler. The red shoveler is a fairly common duck in South America, where it joins the cinnamon teal as the only two blue-winged ducks found on that continent.
Interestingly, despite its small population size and restricted range in North America, the cinnamon teal is the only native dabbling duck that breeds in temperate regions of both the northern and southern hemispheres. Blue-winged teal are largely restricted to North America, although individuals regularly venture into South America. Its Old World counterpart, the garganey, breeds in northern Europe and Asia and makes epic long-distance migrations to its wintering grounds in tropical Africa and Asia.
The blue-winged ducks share several interesting behaviors related to migration, foraging, breeding and courtship that set them apart from other ducks. For example, social foraging, which is rare among other waterfowl, is common among these species. Northern shovelers, whose diet largely consists of tiny aquatic invertebrates, often feed by huddling with their heads down and swimming in a tight circle as they churn the water with their feet. This form of social foraging, known as "whirling," concentrates aquatic insects and plankton on which the birds feed.
Another hallmark of the blue-winged ducks is aggressive territorial behavior during the breeding season. Most ducks have a relaxed form of territoriality, in which they defend their mate or some portion of a wetland from intruding members of their own species, especially females. But the blue-winged ducks are aggressive toward both males and females of their own kind and blue-winged and cinnamon teal are aggressive toward one another on the breeding grounds. This unique behavior may be a consequence of the very close relatedness of these species.
The blue-winged ducks also share several interesting courtship displays. These behaviors include "jump flights," in which competing males appear to leapfrog one another as they jockey for position near an unpaired female. Another frequently observed courtship behavior displayed by males of these species is "head pumping," a repetitive up-and-down movement.
As most waterfowlers know, blue-winged and cinnamon teal are among the first ducks to migrate south in late summer and the last to return north in spring. In addition, they migrate farther south than other North American dabbling ducks and the majority of both species winter in Mexico, the Caribbean and Central America. Northern shovelers are also among the first waterfowl to migrate in fall, usually just behind their blue-winged cousins and large numbers of shovelers winter south of the U.S. border.
Despite the many similarities between the blue-winged ducks, these birds differ from one another in population size and geographic distribution. The breeding range of cinnamon teal is largely restricted to the western United States, where they inhabit marshes and alkaline lakes in the Intermountain West and California's Central Valley. Although locally abundant, their total population, which is thought to number about 300,000 birds, is among the smallest of North America's waterfowl. Given its small population size, limited distribution and early fall migration, cinnamon teal are, not surprisingly, among the most lightly harvested of this continent's ducks.
In contrast, blue-winged teal and northern shovelers are among the most abundant, widespread and frequently harvested of North America's waterfowl. In 2011, populations of both species reached record highs, with 8.9 million blue-winged teal and 4.6 million northern shovelers tallied in the traditional survey area. The majority of blue-winged teal and shovelers breed in the Prairie Pothole Region of the United States and Canada. Large numbers of shovelers also breed on vast inland river deltas in Alaska, while blue-winged teal are highly opportunistic breeders that settle in significant numbers on the southern High Plains when wetland conditions are favorable and occasionally nest as far south as the Texas and Louisiana Gulf Coast.
Why are cinnamon teal not as abundant and widespread as their blue-winged cousins? The answer is not clear-cut, but because of similarities in body size, diets and habitat affinities between blue-winged and cinnamon teal, these species compete for many of the same resources where their ranges overlap. Competition can lead to aggression and because blue-winged teal are more dominant, these interactions appear to play a role in limiting the range expansion of cinnamon teal.
Waterfowl are a marvelously intriguing group of birds, inhabiting diverse habitats throughout the world. Knowledge of species relatedness is not only interesting in itself, but also helps scientists identify shared life histories and common—or different—resource needs among waterfowl. This information helps Ducks Unlimited and its conservation partners provide habitat for multiple species, or conversely, identify specific management actions to benefit particular species of concern.
ID CHALLENGE The wings of blue-winged and cinnamon teal are so similar that it's virtually impossible for trained waterfowl biologists to tell them apart. If not for their slightly larger size and wider and lighter-colored feather quills, the wings of shovelers would be equally difficult to distinguish from those of their smaller cousins.
Based in Lafayette, Louisiana, Dr. Mike Brasher is biological team leader for the Gulf Coast Joint Venture.