Snow swirled about us and punishing winds blew off the frigid Choptank River. Peering through frosted air, we could see scores of ducks huddled close to shore. It was a mixed flock of familiar winter visitors to the tidal rivers of Maryland's Eastern Shore.

A handful of mallards, black ducks and a couple dozen American wigeons were scattered in small clumps among the 150 or so canvasbacks. Farther out, ghostly scoters and buffleheads, partially obscured by the steady snowfall, were rolling in and out of sight in the wind-whipped waters.

A fresh blast of near-gale force wind made it clear-the good birding was about to be trumped by the wretched weather.

Before we turned back to the warmth of the car, I took a final, closer look at the nearby flock. Canvasbacks are perhaps the most beautiful birds in the world, with an elegant shape and arresting color scheme. They were certainly worth another look. That's when I spotted a single duck with a bright yellow eye, gray back and eponymous red head. A male redhead (Aythya americana) was not more than 10 yards away, bobbing among the other birds, taking advantage of the relative shelter of this shallow cove.

Redheads are handsome waterfowl in their own right. The male's color pattern mimics that of the canvasback, but the redhead works with a slightly different palette. He has a high arched back of gray and a black chest. His neck and puffy, round head are a deep brick red. A black-tipped, blue bill and amber eye complete the portrait.

In flight, the redhead shows a white belly and light gray under-wings.

Like most ducks, the female wears a commonplace brown plumage. Even the hen's blue-gray bill is a forgettable muted version of the male's memorable one.

The redhead is a mid-size duck, stretching about 19 inches from tail to bill.

Redheads breed in the Great Northern Plains of the United States and up into the Prairie Provinces of western Canada and central Alaska.

The birds build a floating, vegetated nest on a freshwater lake or pond. The first step out of the nest for these ducklings will be into water.

Females lay about 10 eggs in a clutch. But it might not be in her own nest. Redheads are prolific mooches. Know to scientists as "brood parasites," redheads often lay their eggs in other ducks' nests.

The involuntary foster parent, which may not even be another redhead, will provide the incubation and early care.

Nests can contain dozens of eggs from several hens. One case reported 80 eggs in a single nest. The chances of chicks surviving with such extraordinary clutch size are poor. The large number of initial eggs helps to counter the high nest-mortality rates.

Redhead populations are declining, the result of habitat loss and competition for its selective diet.

Fortunately, the bird is fairly numerous in many of its traditional habitats and is classified as a species of "least concern" for conservation purposes.

After they breed, redheads migrate to warmer climes for the winter. They spread out along the Atlantic Coast, the Great Lakes, the Ohio-Mississippi river valleys, and all across the southern United States. The largest winter populations are found in the Gulf of Mexico.

The lone redhead here on the Choptank may have started his life on one of the prairie potholes of Montana or Manitoba. Next winter, he may switch from the Atlantic Flyway with a Chesapeake destination to the Mississippi Flyway to spend a few months in Mexican waters.

Redheads are diving ducks, surviving on a diet of underwater vegetation. They are partial to eelgrass in the Chesapeake. This underwater Bay grass was once abundant, but pollution has taken a heavy toll. Recently, the gradual rise of water temperatures associated with climate change has made the Chesapeake's waters too warm for this species to thrive. In August 2005, the defoliation of eelgrass in the Bay was associated with record warm water temperatures.

Like worldwide temperature trends, the declining prevalence of redheads in the Chesapeake tells an unmistakable story of climate change. These long-term data are immune to the vagaries of an especially tough winter on the East Coast or the overheated rhetoric of some science deniers.

The bitter wind and stinging snow finally prevailed, and I walked woodenly on frozen legs back to the car. The redhead had done his job. With his handsome shape and colors, he took me away from a bureaucrat's artificial world and let me focus on the reality of this frozen scene of peaceful beauty. And that was enough to warm my heart, no matter what the thermometer said.