Feathered and Fat: A Story of Winter Survival
by Tate Bushell
1/28/2010, page 8

Winter makes life a bit more challenging for us humans as we are forced to wear more clothes, drive more slowly in the snow, split, move and stack wood, and clear our steps of ice. However, these are mere setbacks in our daily lives – extra actions that mark a usually pleasant and often magical season. For our animal neighbors, winter is a much more serious matter. It is a strenuous and demanding time for animals when they are subjected to frigid temperatures and a scarcity of food.
Each species of animal has its own way of navigating through the long, cold winter. Some, like the groundhog and black bear, enter into a state of decreased activity called torpor. Red and gray squirrels spend the fall hoarding acorns and conifer cones to be eaten when winter food becomes less available. Fall skies are filled with migrating birds that seek insects in the south, while most insects of the north either die or overwinter in their own inactive states. Of the birds that stay in Charlotte all year, there is one whose wintering behavior and physiological adaptations are particularly well known among ornithologists.
We know the black-capped chickadee’s call of “chick-a-dee-dee-dee-dee” and recognize it by the black forehead and bib. It is a common bird at our feeders and is an extraordinary winter success story. Haven’t you ever wondered how this tiny bird (weighing just over a third of an ounce) survives sub zero nighttime temperatures and manages to find food when the forests appear so empty?
Like humans, the black-capped chickadee’s first step toward staying warm is insulation. Its feathers hold in body heat generated from a high metabolism and physical activity. The chickadee can expand the volume of its body by puffing up its feathers, which trap more warm air than when they are flattened against the bird’s body. No insulating system is perfect, however, and heat is inevitably lost to the surroundings, mostly from around the eyes and beak. To minimize this loss the chickadee tucks its head into its back feathers during sleep.
The chickadee is at greatest threat of freezing during the long winter nights and employs a number of amazing strategies to keep its body warm. It has a remarkable internal engine which burns calorie-rich fat throughout the night, keeping its body temperature regulated against the frosty winter air.
Studies have shown that chickadees in winter contain around 7% body fat in the afternoon and only 3% in the morning. Astonishingly they have to put on fat during the day so they can burn it at night! Their constant daily forage for food is responsible for this nightly crescendo of fat. Come morning there is no excess fat and they are forced to forage regardless of weather conditions. They spend every waking moment searching for their primary winter foods, seeds and berries, and will feed on fat from dead animals or suet hung by a human if they are lucky.
One study from Wisconsin showed that populations of chickadees are limited by abundance of food and that supplemental food sources (bird feeders) increased winter survival rates. Establishing a feeder on your property can help increase the chances of survival for some lucky birds and gives you a look at their voracious feeding habits! Keep those feeders filled on extra cold days, as the birds will increasingly incorporate your generosity into their feeding schedules.
Interestingly, chickadees announce to one another when a food source has been located. But why would they share precious calories with the group? Many ornithologists consider this to be an evolutionary means of keeping groups foraging together, providing extra eyes to look out for predators like the Cooper’s hawk.
To chickadees fat is survival, so in order to use it more efficiently they have adapted a physiological response to very cold nights. To minimize the amount of fat burned they drop their body temperature from 108° F to 90° F. This reduction of internal temperature operates on the same principle as the heat in your home. It takes more energy to keep your house at 70° F than it does to keep it at 65° F. By dropping their temperature they save energy.
Good luck finding sleeping chickadees. They stay tucked away from the wind by sleeping in a variety of concealed places such as tree cavities, crevices found in wood, or in the dense foliage of coniferous trees. Think about that as you pull your down blankets over your head at night!
The black-capped chickadee is not the only animal that is prepared for a difficult winter life. Each species out there has a history that has shaped its adaptations and strategies. Their stories of survival and physical capabilities move me, and when I consider nature’s power, I feel grateful to be a part of it, for it shows that anything is possible!

Tate Bushell is a graduate student in UVM’s Field Naturalist Program. You are invited to share your winter experiences with him at Tbushell@uvm.edu.

The Charlotte Conservation Commission collaborates with talented area naturalists to provide WILD LIFE nature notes, helping residents understand and appreciate wild nature close to home. Coordinated by Linda Hamilton and Alicia Daniel. For more information about the Conservation Commission, see charlottevt.org.