Confronted by a hungry rattlesnake, a California ground squirrel chucks pebbles and dirt at its enemy and menacingly waves its tail.

Then it really turns on the heat.

Using infrared cameras, scientists at the University of California, Davis, have found that ground squirrels warmed up their tails as much as 12 degrees to silently warn rattlesnakes, which can detect the tiniest of temperature changes.

The report this week in the Proceedings of the National Academy of Sciences provides an unusual demonstration of how animal behavior can evolve in response to specific threats.

Rattlers and California ground squirrels are locked in an epic struggle for which squirrels are surprisingly well-equipped. They are immune to rattlesnake venom and aren’t afraid to use their sharp teeth.

Squirrels deploy their defenses to keep rattlesnakes from snacking on squirrel pups. Scientists looking at the contents of rattlesnake stomachs have found that in the spring and summer months – when pups are born – infant squirrels account for about two-thirds of the rattler’s diet. The snakes don’t try to eat grown squirrels.

Researchers long ago noticed that squirrels used their tails to wave off rattlers, even at night when the effort seemed useless because it was too dark to see.

But snakes’ heat sensors don’t require sunlight.

Scientists staged a confrontation between a snake and a squirrel, separating them with a wire mesh while recording the action on infrared video. The squirrel’s tail shot to a peak temperature of 82 degrees.