By Terry W. Johnson
It was only recently that an Arctic Clipper laden with a full cargo of frigid weather sailed into the Peach State this winter. Of course, when cold dominates our weather we have the luxury of taking refuge in cozy abodes. When we do venture outside, we don heavy winter coats, hats and gloves to ward off the cold.
At best, frigid weather is little more than an inconvenience to most of us.
Such is not the case with our bird neighbors. To them, dealing with extremely cold weather is a life and death struggle. Fortunately, many birds are well adapted to deal with the cold.
One way they keep warm is by fluffing out their feathers to trap body heat. The air found between the fluffed-out feathers acts as an excellent insulation. A Carolina chickadee, for example, uses an intricate network of tiny muscles to fluff some of the 2,000 feathers that cloak its body.
Other birds, like the American goldfinch, grow more feathers as winter approaches. The additional feathers provide added insulation.
Birds also keep warm by shivering. Since small birds are affected by the cold more than larger birds, it is not surprising that they shiver almost continuously when temperatures drop below freezing. In fact, some birds such as the black-capped chickadee (a close northern relative of our Carolina chickadee) can sleep while they shiver.
Shivering can keep an American goldfinch five times warmer than it would be if it was not shivering.
Keeping warm in cold weather also requires more energy just to survive. Hummingbirds can literally starve to death trying to stay warm on a bitter cold night, especially if they have not eaten enough food to fuel their high metabolism. Birds such as turkey vultures and mourning doves are capable of reducing their body temperatures on cold nights, allowing them to conserve precious energy.
A few birds such as hummingbirds and black-capped chickadees carry this to the extreme. These feathered mites will go into torpor to survive the cold. In this condition, the birds remain motionless and their body temperature and respiratory and heart rates plummet. A hummingbird’s body temperature may drop from the usual 107 degrees Fahrenheit to the mid-80s or so when the bird is in torpor.
You would think that since a bird's feet are not protected with feathers they would be vulnerable to frost bite. Actually, they are not. First of all, a bird’s foot has little muscle tissue – tissue that would be highly susceptible to the cold. Additionally, birds will often stand on one foot while keeping the other tucked close to their warm bodies. When the exposed foot gets too cold or tired, the bird stands on the other foot and nestles the foot on which it had been standing among its soft feathers.
Have you wondered how ducks and geese swim about in ice-cold water without damaging their legs and feet? The answer to this perplexing question is simple: They can constrict the veins found along the outsides of their legs and feet. This forces blood closer to warmer blood flowing through arteries from the heart, warming the cooler blood and preventing damage to legs and feet.
Quail will keep warm at night by roosting in a tight circle with their wings slightly elevated. Each bird faces out. The arrangement allows quail to more easily detect predators approaching from any direction and enables the birds to share their body heat, keeping them warmer than if they roosted alone.
Birds will also roost in thick cover, tree cavities or manmade nesting or roosting cavities to ward off cold. Chipping sparrows, northern cardinals, blue jays and mourning doves, for example, will roost in dense conifers and other thick cover on frigid nights.
Meanwhile, woodpeckers, titmice and bluebirds will spend the night in nesting and roosting houses, as well as natural cavities. Interestingly, during extremely cold weather birds often retire to roosts earlier in the afternoon than they would during warmer weather.
There are a number of things you can do to help your bird neighbors survive frigid temperatures. First, provide them with high- quality roost sites such as brush piles, dense shrubs, vines and trees that retain their foliage throughout the winter. When possible, leave standing any dead trees that contain cavities.
Also, erect nesting and roosting boxes in your yard. A variety of boxes featuring different sized holes will benefit a wider variety of wildlife than a number of boxes with entrance holes of the same diameter. When the weather turns cold, safe, warm nighttime roosting sites are just as important as food.
Last, but not least, stock your feeders with high energy foods such as suet and black oil sunflower seeds.
As you can see, wild birds are well adapted to surviving freezing weather. However, you can help them and other wildlife make it through the worst that winter can throw at them.
If you do, you will feel a warm glow during even the coldest weather, knowing that your actions may make the difference between life and death for the birds that live just outside your backdoor.
Terry W. Johnson is a former Nongame program manager with the Wildlife Resources Division, a backyard wildlife expert, and executive director of TERN, the friends group of the Nongame Conservation Section. (Permission is required to reprint this column. Contact firstname.lastname@example.org.) Learn more about TERN, The Environmental Resources Network, at http://tern.homestead.com.
“Out My Backdoor” columns archive.
It was only recently that an Arctic Clipper laden with a full cargo of frigid weather sailed into the Peach State this winter.