Heat up and wiggle
Researchers discover how desert squirrels protect their newborns
Article by Hudson Lofchie
Published in The California Aggie on April 18, 2012
How does a squirrel tell a rattlesnake to stay away from its babies? It heats up its tail. Using a robotic model of a squirrel, researchers at UC Davis and UC San Diego have been trying to find out how squirrels communicate aggression to their most dangerous predator. This heated communication is just part of the behavior that researchers are trying to mimic in an effort to understand how such a small animal manages to ward off such a large adversary.
In the arid desert, the squirrel is not trying to protect itself, but its babies, or pups. During the late spring and early summer, the pups are born, and the rattlesnakes go hunting. Normally, a squirrel would be outmatched and simply run away from the rattlesnake. But when it comes to protecting the pups, running away is not an option. The squirrel needs some way of alerting the snake that it is willing to fight if necessary.
“By heating its tail, [the squirrel] is saying ‘Hey! We are here! We know you are there,’” said Sanjay Joshi, a professor of mechanical and aerospace engineering at UC Davis and one of the researchers on the project. “We discovered that tail-heating is a very important component of communication.”
Heating is an effective signaling method for the squirrels because it drastically increases the squirrel’s visibility to the rattlesnake’s “sight” with infrared. In other words, snakes have heat vision. This observation is the first-ever discovery of animals actively communicating with heat signals.
When a snake encounters a squirrel that is displaying a heated tail, it avoids getting into strike position and getting near the pups. However, sometimes the tail-heating is not enough on its own, so squirrels must use other methods to ward off the serpentine danger. In these occasions, squirrels perform what is called “flagging,” or waving their tail a certain way.
“Snakes will rarely strike at a flagging adult squirrel,” said Rulon Clark, a researcher at the UC San Diego department of biology and another of the head researchers on the project.
In addition to tail-heating and flagging, squirrels have two more defense methods they can employ against rattlesnakes. Squirrels have incredible agility as well as a strong resistance to snake venom.
In addition to the biological and behavioral questions the researchers were trying to answer, they have also been looking to answer a more basic question about robot-animal interaction — how closely to the rattlesnake does the robot have to resemble an actual squirrel to pull off a successful mimicry?
“Simulations in a lab are always different from the true performance in the field,” said Ryan Johnson-Masters, a graduate student in Joshi’s lab.
In both laboratory and field settings, the snake seemed unable to tell the difference between real squirrels and the robotic squirrels that had been designed to mimic the tail-heating and flagging behavior. Engineers had to work closely with biologists to get the design of squirrel characteristics right, and biologists worked with the engineers to gather and analyze the data that the robot delivered.
Much of what is known about squirrel psychology was discovered by UC Davis professor of psychology Donald Owings, who passed away last year. However, the researchers are continuing the work that he started and hope that they will discover many more previously unknown intricacies of animal behavior.