Interesting adaptations allow birds to cope with weather

Published: Sunday, November 18, 2007

This week Lubbock experienced its first really chilly nighttime temperatures of the season, and the birds that stay here year round are exhibiting some different behaviors as they adapt to the cooler days and nights. Mississippi kites, Swainson's hawks and Western kingbirds already packed up and left weeks ago for warmer climates and abundant food supplies in Central and South America.

Regardless of where they live for all or part of the year, birds have a remarkable ability to maintain a constant body temperature in temperate, tropical and extreme temperatures at the North and South Poles.

Some birds raise their metabolic rate to prevent their internal temperatures from falling. Other species, including poorwills, hummingbirds and swifts, enter what is called a state of torpor, when their body temperatures may drop significantly for several hours and sometimes much longer during bad weather.

Carol Lee

Nighthawks and poorwills are admitted to the South Plains Wildlife Rehabilitation Center every fall because they sit like statues on the ground or on fence posts for long periods and people can walk right up and pick them up, assuming they're ill.

Usually, when the bird warms back up and the weather warms, it can be released again. Unfortunately, birds are also targets for predators during this state of minimal activity.

Birds also have a knack for gracefully balancing on one leg while they sleep or rest. At first glance, some think a bird is missing a limb when they see it perched on a single leg. While there are a few one-legged birds in the wild, what people usually see are birds at rest.

Birds have feathers to insulate their bodies, but most birds don't have insulating feathers on their legs, so by tucking a leg up under the breast feathers, one leg can be insulated from the cold. Tucking their heads under their wing feathers also impedes heat loss on cold or windy days.

We have a circulatory system where blood is distributed to our extremities regardless of the temperature outside. Birds have the ability to stop the flow of blood to their feet and retain the warm arterial blood in their body. While a bird's core temperature may be a toasty 104 degrees, its feet may be only a few degrees above freezing in winter. It's not uncommon to see ducks and geese hanging out lazily on the ice when our smaller playa lakes freeze over.

If you go to the coast during winter you'll see dozens of "one-legged" gulls standing on the shore, all minimizing heat loss. It also takes less energy to stand on one leg than it does to stand on two.

On snowy, very cold days in Lubbock, one can see Canada geese lying down, thus keeping both feet covered with their warm down and feathers. Some birds fluff up to increase insulation.

Flamingos and many other birds can stand on one leg for more than four hours at a time and never lose their balance. Even though they're found in warm climates, some think they use the one-legged stance to dry out after standing in wet, muddy environments. Interestingly, another theory is that by standing on a single leg, they change their silhouettes and fool predators into thinking they're just more tall vegetation, even if it is bright pink.

Some ornithologists suggest flamingos even sleep on one leg, essentially turning half of the brain off to rest, and balancing on the leg that is connected to the part of the brain that is awake. One account even suggested that some other ornithologists think flamingos stand on one leg so that ducks only run into them half the time. I guess even the graceful flamingo can be the butt of a joke.

Birds have other behaviors that are linked to warm weather patterns. They love to catch warm rays of the sun on nice days, and will tilt their head up toward the sun, and spread out the feathers one wing at a time and hold that stance for several minutes while they bask.

Birds have no sweat glands, so heat must be dispelled through the respiratory tract by panting. This often prompts questions when we do programs using our great horned owl. When she gets too warm, you see rapid vibration of the upper throat and the thin floor of the mouth; this is called "gular flutter." This pulsation of the upper esophagus occurs in doves and pigeons, pelicans, herons, cormorants, owls, roadrunners and others all use this strategy to thermoregulate.

Birds also develop thicker layers of feathers to combat the cold. The willow ptarmigan, a bird I saw for the first time recently when I visited the Arctic tundra, has water-repellent outer feathers as well as inner feathers. These birds live year-round in the arctic and even have feathers on the soles of their feet that keep their feet warm and also serve as snowshoes to prevent the plump, chicken-sized bird from sinking into the snow.

Whether it's evaporative cooling, standing on one leg, or migrating to a more hospitable climate, our feathered friends certainly know how to beat the cold - and the heat.

CAROL LEE is the executive director of the South Plains Wildlife Rehabilitation Center. She can be reached at spwrc@suddenlink.net.


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