Birds adapt to winter weather

By Charles Seabrook

For the AJC

The birds vying for food at my feeders this week seemed as numerous as ever for this time of year. A Carolina wren called from the woods, and a pesky nuthatch pecked on my house.

Everything seemed normal in the bird world. I had been a bit worried that many of the birds would not make it through the cold that literally froze Atlanta this month. Though some birds undoubtedly succumbed to the numbing chill, most birds obviously came through just fine.

Birds have so many ways of surviving intense cold that I am always amazed at their endurance.

On very cold nights, many Georgia birds seek protection from harsh winds, rain and snow in thick evergreen trees, shrubs and hedges. Several of the birds may fly into the evergreens as a flock and perch near the trunk for added safety from the wind. Flocks of crows and wild turkeys may roost in the evergreens and each individual pool its body heat within the flock.

Many birds — bluebirds, chickadees, titmice, nuthatches, screech owls, downy and hairy woodpeckers and others — that nest in tree cavities during the spring may use those same cavities in winter to ward off night-time cold. Standing dead trees and dead branches make good sites for natural cavities.

Providing winter roosting also is a good reason to leave bluebird nest boxes up all year. As many as half a dozen bluebirds may crowd into a single box and huddle on the box floor for warmth during bitterly cold nights. Chickadees, titmice, nuthatches and downy woodpeckers also sometimes use the boxes to escape the cold.

Birds also have some fascinating physiological and behavioral adaptations for staying warm. Some species such as chickadees go into a state of “regulated hypothermia” on frigid nights. Their body temperature drops 10 to 15 degrees, which saves them about 20 percent of the energy normally required to maintain average body heat.

Many birds grow thicker coats of insulating feathers in winter. An American goldfinch’s winter plumage can be 50 percent thicker than in summer. In addition, birds can increase insulation by 50 percent simply by fluffing up their feathers to trap air near their warm bodies — the reason puffed-up birds are such common winter sights.

In extreme cold, birds also may tuck in their necks, legs and wings to avoid losing heat. If all else fails, they may do what humans do: shiver to generate body heat.

In the sky: The moon will be waxing toward first quarter next week. Look for it to rise in the southwest at sunset and set before midnight, said David Dundee, astronomer with the Tellus Northwest Georgia Science Museum. Mercury is low in the east just before sunrise. Mars rises out of the east just after sunset. Jupiter is in the west at sunset and sets in the west about three hours later. Jupiter will appear near the moon Sunday and Monday evenings.