During the nonbreeding season, black-bellies primarily use mangrove swamps and coastal lagoons to meet their food and cover requirements. However, similar to their goose cousins, black-bellies have adapted to feeding in agricultural environments, frequenting pastures and cattle feedlots as well as harvested rice, corn and sorghum fields when the opportunity presents itself. Fulvous whistling ducks, with their long necks and legs, short tail and broad wings, also look much more like a goose than a duck.
They are very agile on land, standing erect and walking without the waddle so characteristic of other ducks. A tawny brown head, chest, breast and belly distinguish fulvous whistling ducks. Ivory-edged side and flank feathers form a striking border between the sides and back. In North America, the species is most common in Mexico, but also breeds in California, Florida, Louisiana and Texas. Most fulvous whistling ducks depart their breeding range in the United States during September and October to winter in Mexico, returning north again in March and April.
Like black-bellies, fulvous whistling ducks breed during their first year of life. Nest initiation occurs from May through August. Fulvous whistling ducks nest in rice fields and in wetlands, usually over water among water-tolerant grasses and sedges. Females lay 12 eggs on average, and both sexes incubate the eggs. Unlike most species of waterfowl, fulvous and black-bellied whistling ducks do not add down to their nest bowls. Scientists have also observed that fulvous whistling ducks do not cover their eggs when they depart the nest to feed, possibly because of the high temperatures occurring on their southern breeding grounds.
In late August and early September, fulvous whistling ducks concentrate in flooded rice fields and large ponds. This species is noted for its nocturnal feeding in rice fields, where one observer vividly described a scene in Louisiana in 1943: "When we reached the fields and levees just before dusk, not a duck was seen or heard. Within a few minutes, on they came in no particular formation as with ordinary ducks - singly, in pairs, in companies of a dozen or more, and in irregular groups, and in twenty minutes they were flying and squealing everywhere, hundreds of them." In October, flocks move to coastal marshes where they feed predominantly on the seeds of aquatic vegetation. In November, a general exodus occurs to the east and west coasts of Mexico, where the birds spend the winter on coastal lagoons and rice fields.
Comprehensive population surveys of whistling ducks are lacking. Most of our information comes from mid-winter surveys conducted by the U.S. Fish and Wildlife Service and occasional breeding season surveys associated with short-term research projects. Limited data suggest a relatively stable breeding population of around 20,000 fulvous whistling ducks in Louisiana and Texas. Significant breeding populations also exist in Mexico, but surveys are insufficient to document population status and trends. Many breeding populations in both the United States and Mexico have historically been associated with rice culture. Since the 1980s, rice acreage has declined dramatically in Mexico, Louisiana and Texas. Much of this land is now being used for dryland crops and pasture, which provides little habitat for breeding fulvous whistling ducks.
Available information for black-bellied whistling ducks suggests a stable population in Mexico and growing population in Texas. About 80,000 birds are generally counted along the east and west coasts of Mexico each winter, and researchers estimate a breeding population of several thousand in southern Texas.