Feeling the heat: Ground squirrels heat their tails to discourage rattlesnake attack

Abstract

Predators have a remarkable evolutionary effect on the morphology and behavior of their prey (1). In their attempt to reduce the likelihood of being killed, prey species have evolved a variety of counterstrategies, including the ability to communicate directly with their predators to discourage pursuit or attack. Stotting, when ungulates jump up in a stereotypical stiff-legged display, is a visual signal of unprofitability to hunting carnivores, and the alarm calls and mobbing behavior seen in birds and mammals may also discourage pursuit. Indeed, predators are hypothesized to be the ancestral target of alarm communication in rodents (2), systems that ultimately have been exapted to serve sophisticated conspecific warning functions (3). Communication requires a signaler to influence the behavior of a receiver by using one or more modalities. Previous studies have focused on visual, acoustic, seismic, and olfactory modalities, but in this issue of PNAS, Rundus et al. (4) have discovered that California ground squirrels (Spermophilus beecheyi) communicate by means of a private infrared channel specifically to a major predator that is uniquely sensitive to infrared radiation—rattlesnakes (Crotalus oreganus)—whereas encounters with infrared-insensitive gopher snakes (Pituophis melanoleucus) elicit snake-directed tail flagging without the infrared signal.