We have been seeing chickadees at our feeders this winter, taking sunflower seeds and flying off with them. They somehow made it through the frigid early January temperatures. But how?
This interesting article by Mike Wilpers, a member of Friends of Sligo Creek, explains their strategies – including a phenomenal memory that helps chickadees find the seeds when they need them. – Marjorie Rachlin
by Mike Wilpers
Five basic adaptations help our Carolina chickadees (and their close cousins, the tufted titmouse) get through the kind of brutal cold we recently experienced.
Like many birds, chickadees and titmice fluff-out their feathers in a cold snap, which makes them look fat but adds many layers of insulating air between their bodies and the cold. Studies have shown that bird feathers provide much better insulation than mammal fur.
A second way they maintain daytime body temperatures is to shiver, which burns calories but generates heat.
Another adaptation allows chickadees to drastically reduce their body temperature at night by more than 50 degrees Fahrenheit, from 108 to about 50. This process of “nocturnal hypothermia” saves considerable energy because the birds don’t burn precious fat to maintain their daytime body temps over the long winter nights, which they spend alone in tree cavities.
A fourth adaptation to cold is their ability to store vast numbers of seeds in hidden caches all over their huge flock territories in winter. A single chickadee can cache tens of thousands of seeds a year, each seed in its own hiding place, usually behind strips of bark. Some chickadees have been observed caching 1,000 seeds in a single day.
This caching of seeds would be useless without the chickadee’s astonishing ability to remember their locations, which they do almost without fail over winter territories up to ten square miles. Lab studies show that chickadees remember thousands of seed locations by relating them to angles or distances from landmarks.
Their remarkable spatial memory is created by a whopping 30 percent increase every fall in the capacity of the hippocampus, that portion of their brains (as in mammals) devoted to spatial memory.
In 1994, it was discovered that chickadees add a tremendous number of nerve cells to this part of their brains as winter approaches. Since then, scientists have shown that seasonal brain enlargement in chickadees is greater in more northern latitudes and at higher elevations, even in the same species.
Since severe cold (and predators) inevitably take their winter toll on chickadees, their backup plan is to rear up to nine chicks every spring, which improves the chances that a few will make it through the winter, no matter how cold it gets.
Here’s a nice video about bird survival in winter and an NPR piece on brain enlargement in fall chickadees. For a scientific review of chickadee caching, and seasonal changes in their brains, see pages 9-23 of this online excerpt from The Ecology and Behavior of Chickadees and Titmice, K. Otter, ed., 2007.
This article was adapted with permission from the January 2018 FOSC newsletter. Learn more about Friends of Sligo Creek at fosc.org.