for National Geographic News
Scientists who study "cross-dressing" garter snakes have come up with a new answer to the question: "Why do they do it?"
Nearly 20 years ago, researchers discovered that some male garter snakes mimic female behavior when they emerge from hibernation. This behavior is not unique in the wild; in several species the males are known to pose as females.
The common assumption has been that the "she-males" are seeking a reproductive advantage or attempting to avoid aggression from larger males.
Not so, at least as far as garter snakes are concerned, reports a team of U.S. and Australian scientists in the November 15 issue of the journal Nature. The researchers have concluded that the male snakes pose as females simply to get warm and to reduce their exposure to predators.
The idea that the she-male trait evolved as a response to environmental factors (natural selection) instead of as part of a reproductive strategy (sexual selection) is a new one.
Rebounding from Hibernation
Manitoba, Canada, is famous for having the largest concentration of snakes in the world. The garter snakes (Thamnophis sirtalis parietalis) leave their underground dens by the thousands in early spring, after eight months of hibernation.
The males emerge first—cold, weak, slow, and highly vulnerable to attacks from predators such as crows, magpies, and other birds.
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