How Do Tiny Chickadees Survive the Frigid Cold?

Carolina Chickadee - Photo Earl Harrison
Carolina Chickadee with Seed - Photo Joe Twiss via Flickr

Carolina Chickadee with seed ready to hide (cache) for eating late – Photo Joe Twiss via Flickr

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.

Chickadee Drawing - NPR

Chickadees can add 30 percent more brain cells in fall for remembering hundreds of hidden seed locations. (NPR drawing)

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.

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.

Nutcracker Seed Memory

Lab studies show that chickadees remember thousands of seed locations by relating them to angles or distances from landmarks. (Drawing from NationalGeographic.com)

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.

For more information, check out this video about bird survival in winter and read this 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 is reprinted through the kind permission of the author, Michael Wilpers. It originally appeared in the newsletter of the Friends of Sligo Creek (Maryland).

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