Brainy Chickadees Shun 'Snowbird' Label

Their fair-weather cousins have long since departed, migrating for warmer climes and a more varied menu. Black-capped chickadees stay, appearing as little puff balls at Alaskan's bird feeders even on the coldest days of the winter. Chickadees aren't built to take an Alaska winter, but they thrive with unique adaptations to life in the north.

Bigger is better when it comes to surviving an Alaska winter without artificial heat, said Pierre Deviche, an associate professor of animal physiology with UAF's Institute of Arctic Biology. Just like a large cup of coffee cools more slowly than a small one, a moose retains body heat more efficiently than a fox, Deviche said. A fox needs to produce more heat relative to its body size to keep warm.

Weighing about as much as a handful of paper clips, a chickadee overcomes its size disadvantage with physical adaptations and by using their tiny, black-and-white heads. Susan Sharbaugh, a doctoral student at the UAF Department of Biology and Wildlife, said that beginning in late July in the Interior, chickadees begin wedging seeds, insects and other food into tree bark and other crevices.

Unlike squirrels, who create massive mounds of spruce cones for munching later, chickadees "scatter hoard," Sharbaugh said. Chickadees leave thousands of seeds cached throughout the half-mile range in which they spend their entire life. Later in the winter, perhaps when a bird feeder runs out of sunflower seeds, chickadees are somehow able to find the seeds they cached months earlier.

"These guys have a fantastic memory," Deviche said.

Studies of chickadee brains reveal that the volume of the hippocampus, an area of the brain linked with memory, varies with the season. In fall, when a chickadee is hiding food, thehippocampus expands. In the spring, when there's no more need to find cached food, it contracts, Deviche said.

In addition to brains that bulge with the season, chickadees physically adjust to a cold climate in many ways. In fall, they begin shivering. Although it's not visible at the bird feeder, chickadees' chest muscles, called the pectoralis, repeatedly flex to generate heat. That heat is contained by the air trapped within a chickadee's downy coat.

A chickadee's feathers are amazingly efficient. Sharbaugh said when it's 40 below Fahrenheit outside, a chickadee's feathers rise to create an inch-thick coat that provides a halo of warmth. The difference in temperature of the chickadee's body core and the environment an inch away is 148 degrees. Try standing outside at 40 below in an inch-thick coat. Brrr.

Unlike common redpolls, one of the other tiny species of songbirds that winters in Alaska, chickadees don't have an internal bag for storing food, called a crop. Instead, chickadees must eat small meals, digest them, then eat again. Because they only feed in daylight, their window of opportunity is woefully small in winter.

To compensate, they eat as much as they can, adding fat each day that amounts to 10 percent of their body weight and burning it at night. This is like a 150-pound person eating enough to weigh 165 by day's end, then using enough energy at night to be back to 150 by the morning.

"It's a huge physiological feat," Sharbaugh said.

Where Alaska chickadees spend the night is a mystery, but Deviche and Sharbaugh believe they ball themselves up in a crevice or cavity by themselves or perhaps roost in spruce branches. Once they settle in for the night, chickadees turn down their internal thermostats to save energy, Sharbaugh says.

From a normal body temperature of about 108 degrees, chickadees cool down to about 90 degrees when roosting. Despite the energy savings of this method, Deviche says in winter it's almost impossible to find a fat chickadee in the early morning.

Researchers notice a difference in chickadee behavior during cold snaps; the usually social birds apparently ignore each other and focus solely on filling up.

Seems as though chickadees have a few traits in common with we humans, another organism that arguably wasn't built to survive an arctic winter.