Լ����Ƶ

What’s brown and black but white all winter? The ptarmigan is unique among birds for molting into snow-white plumes for half the year. In fact the three species of ptarmigan—rock, willow, and white-tailed—may be among the best-adapted birds for surviving the frigid winter temperatures of northern climes and high elevations.

Like other critters that live in snowy places, including the ermine and the Arctic fox, the ptarmigan’s gray-brown summer garb transforms into a brilliant bright white each year when the snow begins to fall. (Technically, the white-tailed and rock ptarmigan have black outer tail feathers, but they’re barely visible under most circumstances.)

But blending into the snowy background is hardly the only trick these birds possess. Grouse in general are unusual in part for their seasonal footwear. Each fall the chainmail-like scales on their feet give way to tiny bristly projections called pectinations that nearly double each foot’s surface area, making it easier for the birds to navigate in snow. In spring the pectinations fall off. The ptarmigan, however, has an extra level of protection: Instead of fleshy pectinations, these birds have expansive foot-feathers that act like insulated snowshoes, increasing both surface area and warmth.

With ptarmigan, , adjusting their diet is crucial to surviving the cold. Michael A. Schroeder, a wildlife biologist at Washington Department of Fish and Wildlife, explains that the ptarmigan gets by on a remarkably plain diet of dry leaves and buds. The one catch is that unlike its similar summer fare, the ptarmigan’s winter diet isn’t a good source of moisture. The solution to this is simple: “They just go crazy eating snow all the time,” Schroeder says.

Still, the real test of winter survival is nightfall. Here again, there’s a ptarmigan advantage. Like other grouse, these birds don’t sit out in the elements overnight or expose themselves by roosting in a tree. Instead they burrow into the snow, creating cozy caves. The snow roost, explains Schroeder, can be a foot deep and offers a warm, comfortable alternative to frigid surface temperatures.

Despite these impressive adaptations, the bad news may be that the ptarmigan is specialized for a habitat that’s rapidly disappearing. Schroeder, who has worked with grouse for more than three decades, is among a group of researchers trying to understand how the ptarmigan is responding to climate change.

Other Arctic and alpine animals are under threat as their habitat literally melts around them, reducing their range and isolating ever-more fragmented populations. Although it’s too soon to tell how the ptarmigan will fare, for now Schoeder and his colleagues have hope. After all, if these birds can survive the very worst of winter, perhaps with a little human help they can handle our warming world as well.