Transcript:

If you were a squirrel, would you take on a rattlesnake? I'm Jim Metzner and this is the Pulse of the Planet, presented by DuPont. Well, it's hard to imagine a squirrel teasing, harassing, or even pouncing on a snake, but that's exactly what can happen when an adult California ground squirrel encounters a Northern Pacific rattlesnake, which could be sizing up the squirrel's pups as prey. Mother ground squirrels have been known to kick dirt at, even nip at, an approaching snake. And it's not as foolhardy as it may sound, according to Don Owings, of the University of California, in Davis.

"The adults can press and harass rattlesnakes enough to make them rattle, and they're able to extract important cues about the danger they face from the rattlesnake, from the rattling sound."

Well that's because a smaller snake, that's less menacing, has a slower, quieter rattle...

ambience: Small snake rattle

A larger snake, which is more dangerous, has a louder, faster rattle....

ambience: Large snake rattle

Now, if the mother squirrel decides that an intruding snake is not that dangerous, she may continue provoking it until it gives up and slithers away. But if she hears a louder rattle of a more lethal snake, then she's likely to back off, and may even try to move her babies to another burrow. Either way, the mother's not putting herself in mortal danger by challenging the snake, because over generations, adult ground squirrels have evolved immunity to snake venom.

"The youngsters don't have as much of the venom-neutralizing ability, and so they can be killed by the venom. The adults can be injured, but not killed, by rattlesnake venom, and so they can be pretty assertive when their youngsters are threatened, and so they can actually confront the rattlesnakes."

Pulse of the Planet is presented by DuPont, bringing you the miracles of science, with additional support provided by the National Science Foundation. I'm Jim Metzner.