Compare them to the everyday Mallard and you’ll see that whistling-ducks are no ordinary ducks. They’re lanky, long-legged, long-necked, with big, broad wings. They make loud whistling cries as they fly around by day or night. Unlike typical ducks, male and female whistling-ducks look alike. Both sexes take part in incubating the eggs and tending the young, duties that no male Mallard would ever consider. And some whistling-ducks regularly perch in trees and nest in tree cavities—in fact, they used to be called “tree ducks,” and they belong to the genus Dendrocygna, which translates roughly to “tree swan."

Eight species of whistling-ducks occur around the world, mostly in tropical and subtropical regions. Only two are found in the United States. One, the Black-bellied Whistling-Duck, earns the “tree duck” badge, often perching high in bare branches and nesting in tree cavities—or in nest boxes provided for it. Long a resident of southern Texas, it has greatly expanded its U.S. range in recent decades. The other species, Fulvous Whistling-Duck, nests on the ground and generally avoids trees. Its range north of the Mexican border also has gone through some remarkable changes; oddly, most birders don’t realize the extent of those range shifts.

(Kenn Kaufman's Notebook is a regular column featuring original artwork and essays by Kaufman, a field editor for Audubon, and a world-renowned bird expert, author, and environmentalist.)

The early record is sketchy, but in the area that’s now the United States, Fulvous Whistling-Ducks apparently didn’t arrive until the mid-1800s. For the last century they’ve been present most consistently in coastal Texas, expanding into southwestern Louisiana in the 1930s. In Texas and Louisiana they live mainly in rice-growing country. Their numbers dropped sharply in the 1960s, probably because of pesticides applied to the rice, but populations recovered somewhat in the 1970s and have fluctuated ever since.

Farther east, wandering flocks of Fulvous Whistling-Ducks started showing up increasingly often in Florida in the 1950s, and they were found nesting there in 1965. They’re reasonably common in Florida to this day, especially in areas just southeast of Lake Okeechobee.

And to the West, California has seen the biggest changes. Fulvous Whistling-Ducks spread north into the state in the late 1800s and were nesting there at least by the 1890s. During the first half of the twentieth century, they were widespread in the southern half of the state, both in the interior valleys and along the coast, as far north as San Francisco Bay. Then they started declining. By the 1990s only a few pairs nested at wildlife areas near the Salton Sea. The California Bird Records Committee, which keeps a close eye on every species within their borders, downgraded the whistling-duck from “N” (for a regular nesting species) to “n” (for irregular nesting) in 2003. Now it’s on the committee’s “Review List,” averaging fewer than four records per year in California, a shocking change for a duck that used to be a common breeder.

Such large-scale shifts on the map seem to be pretty standard for Fulvous Whistling-Ducks throughout their worldwide range. They've colonized several islands in the Caribbean during the last century. In parts of South America and Africa, flocks move around considerably in response to wet and dry seasons. Flocks from Africa or India have wandered to the Middle East, Europe, and Southeast Asia.

In fact, wandering around seems to be one of the defining habits of the species. When the birds wander, they do it in pairs or flocks, not just singly. Birders know that this duck might show up practically anywhere. There are scattered records throughout the lower 48 states, north to New England and the Dakotas, and records for at least six Canadian provinces. Whistling-ducks may look a little odd in flight—big feet trailing behind them, long necks drooping—but clearly they are strong fliers, and they readily take to the air to go exploring.

Although they sometimes visit small, tree-lined ponds, Fulvous Whistling-Ducks definitely prefer wide-open spaces. Some of the biggest flocks I ever saw, years ago, were in coastal marshes of southeastern Mexico. I had stopped at a point where broad marshes lined the highway. It was near sunset, and flocks of Fulvous Whistling-Ducks filled the air; in the evening light their colors were stunning, their blackish underwings contrasting with the creamy butterscotch hue of their body feathers. I watched them circling against the shadowy outlines of the Sierra de los Tuxtlas off to the northwest, against the sky, against the sun-washed clouds, while their hoarse whistling-duck whistles echoed around me.