A Tail of Survival

When confronted by rattlesnakes, California ground squirrels employ a key defensive tactic to stave off one of its fiercest predators:

They wag their tails.

SDSU biology professors Rulon Clark and Matthew Barbour, along with researchers at University of California Davis, made the recent discovery.

“We’re shedding light on all of the nuances of what’s going on between this specific predator and prey interaction,” Clark said.

“Robo-squirrel”

Using a robotic squirrel developed by researchers at the University of California Davis, Clark and Barbour recreated ground squirrel and rattlesnake interactions in their natural environments.

“It is very important to recreate behavior of the squirrel in a way we can control all of its movements,” said Clark, whose team used video surveillance to collect data. “Changing different aspects of the Robo-squirrel and watching how snakes respond to these signals is something we could never do using real squirrels.”

Tail wagging dual function

After analyzing field video of the encounters between rattlesnakes and the Robo-squirrel, a dual function of a squirrel’s tail wagging was revealed.

Ground squirrels wag their tails to warn rattlesnakes that they are prepared for an attack, and simultaneously as a signal to other squirrels of potential danger.

Clark explains that rattlesnakes rely on stealth and ambush, and attacks are similar to a gun with one bullet. A rattlesnake coils up waiting for its prey and then pounces, but if the snake were to miss then the prey could easily get away.

When a squirrel shakes its tail it emits an infrared heat, a signal that only rattlesnakes are able to detect, and warns the rattlesnake that it’s prepared to flee and dodge an attack.


Predator and prey co-evolution

Snakes and Squirrels have co-evolved as predators and prey for generations.

“Evolving adaptations and counter-adaptations that allow species to avoid being eaten or obtain a meal respectively, is a powerful evolutionary force,” Clark said. “It’s responsible for shaping lots of species and ecosystems.

“This snake-squirrel system is one of the best documented examples we have.”