Kinglet Buddies

Evolutionary Biology Program director Irby Lovette recounts how a simple observation solved a longstanding mystery about how kinglets keep warm in winter

Golden-crowned Kinglet

Photo by Donald Waite/CLO

Golden-crowned Kinglets are tiny birds that weigh less than two pennies, yet they overwinter in northern forests where temperatures often drop far below freezing. Because small birds lose heat much faster than larger birds, scientists have long been puzzled by how kinglets make it through cold spells: calculations have shown that kinglets should lose more energy during the night than they could possibly gain back during the day by eating insects.

Sometimes simple observations triumph over complicated calculations. It is a rare scientific paper that contains a sentence like ?I saw three kinglets when I was perched about 12 meters up in a spruce tree,? but what Bernd Heinrich (Wilson Bulletin, June 2003) found in the treetops on a cold Maine night has solved the mystery of how kinglets keep warm in the winter.

Two groups of kinglets observed by Heinrich conserved heat by huddling tightly together throughout the night. By turning their tails outward and tucking their heads into their feathers, they collectively lowered their surface-area-to-body-size ratio and thereby greatly reduced their heat loss. In a sense, they turned themselves into a single, larger bird. The answer to the mystery: kinglets survive the cold by cuddling.

Biologist Bernd Heinrich made dozens of attempts to follow kinglets to their roosts at night before he finally found a group of three huddling together. Later, he observed and sketched another group of four kinglets roosting together in a pine.

Sketch by Bernd Heinrich

This observation also solves a secondary puzzle: why do kinglets flock during winter? In cold climates, kinglets have to huddle to survive cold spells, making it essential for each bird to stick close to a group of buddies so that they eat as long as it is light but still find each other fast as the sun goes down.

—Irby Lovette

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu