SFSU Biologist Deciphers Desert Animals' Whistles And Drumbeats

January 30, 1998

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 evolution of group living for defense, Randall notes. This social structure, in turn, would boost the value of complex communication such as that developed by the gerbils. Interestingly, our early ancestors probably underwent a similar sequence of developments out on the African plains: daytime activity, group living, complex communication supporting cooperation. This is widely thought to be the pattern that, along with greatly increasing brain size, led to the human hallmarks of language and culture.

Although drumming has been noted in deer, rabbits, prairie dogs, and other animals, Randall's study is the first to investigate the entire communication system of drumming species. She reported her findings today (January 30) at the annual Winter Animal Behavior Conference in Jackson Hole, Wyoming.

Last year, in Uzbekistan, north of Afghanistan, Randall established that adult gerbils whistle and stomp far more often and more intensely when young pups are still living at home -- strong evidence that they are trying to communicate an urgent sense of danger to their vulnerable young. In addition, pups and other family members head for cover when they hear the faster whistles and the stomping, suggesting that these signals are perceived as signs of danger too. By contrast, kangaroo rats don't respond to a neighbor's foot stomps, supporting the conclusion that these solitary rodents don't use stomping to warn each other of an approaching predator.

Randall used playback experiments to test the gerbils' responses to different kinds of sounds. She played the taped sounds of moderate and then rapid whistles, and found the animals headed for the burrows more quickly when they heard the rapid whistles.

This spring, she returns to the plains of Uzbekistan to determine if gerbils produce different signals in the presence of different predators, say a polecat or fox versus a snake. Recent research on vervet monkeys and prairie dogs has shown these animals give different calls to indicate a slithering snake or a soaring bird of prey. Their cohorts seem to recognize the differences. For example, vervets dive for cover when the signal is "Eagle!" but scramble up a tree if the danger is a cheetah.

Randall's research has been supported by the National Geographic Society and the National Science Foundation.

San Francisco State University

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