Hot tail gives warning

Ground squirrels can heat up their tails to signal and perhaps taunt rattlesnakes.

Messages come in many forms. In the case of ground squirrels, a hot tail seems to mean: “Don’t mess with me.” But only when the squirrel is talking to a rattlesnake.

Scientists from California discovered the unusual behavior by filming squirrels with special infrared cameras that show how hot things are. Rattlesnakes have their own infrared sensors, and the researchers suggest that the squirrels use heat to send a signal to the dangerous snakes.

This is the first known example of an animal sending out infrared signals for any reason.


California ground squirrel.


Gary R. Zahm, U.S. Fish and Wildlife Service

The scientists filmed 12 adult California ground squirrels in a series of sessions that lasted 10 minutes each. In some sessions, the squirrel could approach a cage holding a venomous rattlesnake. In other sessions, the cage held a gopher snake, which isn’t poisonous and doesn’t sense infrared radiation, but could still eat a squirrel’s young.

Normally, the tails of ground squirrels are cooler than their bodies. During sessions with rattlesnakes, though, the temperature of a squirrel’s tail would rise 2 degrees Celsius at both the tip and the base.

Next to a gopher snake, on the other hand, the temperature of the tail’s base rose just 0.2 degrees C. The tip temperature rose half as much. The researchers were surprised at the dramatic difference in the response of ground squirrels to the two snake types.


In images from an infrared video, a ground squirrel’s tail glows (left) when the rodent is harassing a rattlesnake, which has infrared sensors. The tail doesn’t heat up (right) during a spat with a gopher snake, which doesn’t detect infrared radiation.


Aaron Rundus

In the wild, California ground squirrels will often harass a rattlesnake if they encounter one. They’ll run around it, kick sand at it, nip at the snake’s tail, and wave their own tails back and forth in a display called flagging. Hot tails might be the final straw that persuades the snake to slither off.

Squirrels have good reason to dislike rattlesnakes. The slithering animals like to eat squirrel babies. The youngsters make up about 69 percent of a rattlesnake’s diet during the season when the pups are young.

To better understand how hot squirrel tails affect rattlesnakes, the researchers are building a robotic squirrel. The robot will do the flagging display, just like a normal squirrel, but people will control whether the tail gets hot.

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