Annals of science:
Squirrels wield a hot, secret weapon - life - 13 August 2007 - New Scientist: Jeff Hecht: Squirrel waves hot tail at rattle snake--Watch the full-size video; Squirrel waves cold tail at gopher snake--Watch the full-size video: It's Californian ground squirrel versus rattlesnake in a potentially lethal showdown. But the squirrel has a secret weapon that until now has remained invisible to the human eye. The ground squirrel heats up its tail then waves it in the snake's face - a form of harassment that confuses the rattler, which has an infrared sensing organ for detecting small mammals. This defensive tactic remained invisible to biologists until they looked at the animals through an infrared video camera. Now they believe that many other animals might be using infrared weaponry to ward off potential predators. Young California ground squirrels (Spermophilus beecheyi) are easy prey for snakes, so protective adults harass the predators while puffing up their tails and wagging them.
Graduate student Aaron Rundus and his supervisor Donald Owings of the University of California, Davis, wondered how this might affect the snakes’ interaction with the adult squirrels. So he borrowed a $35,000 infrared camera from another scientist and spied on squirrel-snake stand-offs. He saw the adults’ tails heat up, presumably due to increased blood flow, when they were warning rattlers away – making the squirrel appear larger to the snake’s infrared organ. Confronted with a gopher snake, which has no infrared sensory organ, the squirrels wagged their tails but didn’t bother to warm them up first.
Tests with robotic squirrels confirmed that a warmed squirrel tail made rattlesnakes more likely to act defensively, say Rundus and Owings.
The squirrels themselves do not see in infrared, so they cannot see another squirrel's tail heating up. But the snakes can, proving that the squirrels have evolved a specific way to deter rattlesnakes. “It taught us to focus on the perceptual world of the animal we’re studying” rather than thinking only of human perceptions, says Rundus.
Perhaps the scariest thing here is that UC Davis has developed "robotic squirrels"--I assume as part of a dual-purpose research project.