California ground squirrels have it rough, facing carnivorous mammals on the ground and dodging raptors diving from the sky. Unlike any other animal known, however, these squirrels have an amazing defense technique to scare off threatening rattlesnakes: They heat up their tails.
To the naked eye, squirrels defending their pups look pretty much the same whether the predator is an infrared-sensitive rattlesnake or a gopher snake: They make cautious approaches, alter their posture, swish their tails back and forth, and sometimes try to kick pebbles at the enemy.
But infrared video, which measures temperature, shows them treating the two species differently. When confronting a heat-sensing rattlesnake, the squirrel’s tail warms up a few degrees; not so when the squirrel faces off with a heat-blind gopher snake. Other physiological measures of fear, like hair standing on end, were the same no matter which snake they faced.
Biologists at the University of California at Davis reported in September that tail waggling alone is enough to make a snake shift to defensive behavior; increased infrared radiation must be that much more impressive to a rattlesnake, helping convince it that this “glowing” squirrel will not be an easy target.
“When we look at animal systems and try to understand behavior or communication, we have to do so from the perspective of the animals we’re watching,” lead author Aaron Rundus says. “There are lots of things—like infrared signaling—that go on that are apparent only to the animals.”
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