SAN FRANCISCO--When a kangaroo rat encounters a threatening snake, he launches into a round of stomping, essentially to say, "Stay away." But when his relative, the great gerbil, sees a predator approach, the gerbil signals something quite different: "Run for cover, children! There's danger near!"
Toiling in the deserts of Central Asia and the American Southwest, a San Francisco State University biologist has deciphered the system of signals the two species use in response to predators, and has discovered that the gerbils use a variable warning system to alert their kin to the degree of danger.
Communication style seems to come down to lifestyle. Kangaroo rats in the deserts of California, Arizona, and New Mexico live in self-reliant solitude. Nocturnal, they ward off both competitors and predators by foot-drumming. But their genetic cousins, the super-social great gerbils of Central Asia, rely on each other when danger is near. Active during the day, when the threat of predation is high, they have developed two kinds of whistles and a pattern of ever-accelerating foot-drumming in response to a stalking snake or fox. Unlike kangaroo rats, their motives are altruistic. The gerbils live in tight, cooperative family groups, and adults whistle and foot-drum to warn their kin to hide.
"The kangaroo rats appear to be trying to convince an approaching snake or other predator that they are vigilant and can't be caught," says Janet Randall, an animal behaviorist and SFSU professor of biology. "But gerbils warn each other of risk. Adults appear capable of communicating the degree of danger to their colony." An upright posture or moderate rhythmic whistling evokes vigilance from family members, but no fleeing. But when an adult speeds up to double-time whistling and foot thumping, kinfolk head for the burrows.
The increased vulnerability to predation faced by animals active during the day could well have favored the e
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Contact: Wallace Ravven
wravven@sfsu.edu
415 338-6747
San Francisco State University
30-Jan-1998