February 18, 2009
By Susan Benson,
CNHM Director of Education
While I continue to keep warm with my furnace and new comforter, a black-capped chickadee has a number of amazing adaptations for staying warm throughout the winter that far surpass my own. For a bird that rarely lives more than thirty months, winter is a most challenging time for a chickadee that weighs less than my favorite chocolate bar or a few paper clips (one-half an ounce.) Food, brain, feathers, and body work together to keep this backyard bird favorite alive.
Chickadees eat mostly insects, fruits and seeds. During the winter they consume about ten percent of their body weight daily, which means they have to eat, a lot, all day long. In the fall, a chickadee's brain changes as their hippopocampus expands, improving their memory ability. During this time, they stash seeds in pre-selected roost cavities, and months later can recall where those sites are located. In the winter, a time when fruit and insects are scarce, they alter their main food source to the more abundant coniferous seeds, a food high in oil and fat content. Chickadees have even been observed taking fat from previously scavenged dead animals, which serves as an excellent source of calories. Some food chickadees eat is chemically changed into energy reserves that are stored for heat energy at night. By morning, when those reserves are used up, they get chilled and need to eat again, which is why chickadees frequent bird feeders so often in the morning. A study in Wisconsin has shown that birds depending upon bird feeder sunflower seeds do not survive better than those who do not. However, scientists discovered that when winter temperatures are lower than ten degrees, chickadees that access bird feeders can double their survival rate compared to chickadees without feeder seed availability. Although we can certainly appreciate our simplicity of one-stop shopping at our local grocery store as preferable to the food gathering life of a chickadee, we can at least envy their ability to pig out daily without gaining any weight.
While we discuss the R-value of our home's insulation, a chickadee produces more feathers for warmth throughout the winter. The outer feathers have hooks called barbs that zip together to create a wind barrier, while the under feathers are down, which when fluffed, could be considered a human homeowner’s dream because of its insulation value. As a chickadee fluffs its feathers to create an inch-thick coat, they can maintain a temperature of over 100 degrees Fahrenheit (F.) even when outdoor temperatures are at zero degrees (F.). Certainly our reliance on down feathers in winter coats is a tribute to our feathered friends and their ability to survive cold weather conditions.
While hypothermia is a status which humans avoid, chickadees experience it almost nightly when temperatures are very cold. Although their normal daytime temperature is 108 degrees (F.) they regulate their body by decreasing it fourteen to eighteen degrees (F.). This ability to "turn down the thermostat" allows chickadees to conserve twenty-five percent or more of their hourly energy expenditure. As the night cools, their chest muscles also begin to shiver in order to generate heat. Their friendly social nature as they stick together in flocks during winter is also an advantage. They can roost together in tree cavities to share body heat and save energy. During extreme cold, they might not leave their roosts at all. Finally, another body adaptation is related to their bare feet. Chickadees slow down the blood circulation to their feet just enough to keep these extremities from freezing, bringing a whole new meaning to the idea of "cold feet." This combined set of adaptations, although not exclusive to chickadees alone, is amazing!
Whether you are hearing the spring "fee-bee" of a chickadee in your yard, or observing a fluffed up bird through the window at your feeder, these birds can surely be appreciated and enjoyed. Next time you fill your feeders, you can be assured that you are contributing to the successful survival of many of your backyard birds. Perhaps you enjoy them for their ability to thrive in any condition, for displaying a continuous show of beauty, an acrobatic flight or their curious behaviors and activities. Whatever the reason we appreciate them, we can find many positive abilities in a chickadee that could be a model for human behavior.