Thursday, October 8, 2009

‘Leopard Behind You!’

I'd like to continue Predator Appreciation Month with reflections on one of the more intriguing effects that predators can have on their prey: the development of a vocabulary of alarm. (Or should that be "an alarming vocabulary"?)

Vervet monkeyThis isn't a complicated vocabulary, with thousands of words. Nonetheless, it's clear that for many animals, alarm calls are more than simple squawks of fear. Vervet monkeys, for instance, use different sounds to warn of different types of predator. "Leopard!" is not the same as "snake!" or "eagle!" If you hide a loudspeaker in the bushes, and startle unsuspecting monkeys by playing recordings of "snake!" at them, they will look around at the ground. "Eagle!" makes them look up. "Leopard!" sends them scampering to the trees.

Vervets aren't unique. Other primates — including Diana monkeys and Campbell's monkeys — also distinguish between eagles and leopards. (Diana monkeys are elegant animals, with fur of several colors. Also, like male vervets and Campbell's monkeys, male Dianas have a scrotum that's a tasteful shade of blue.)

Diana mokeysSome animals make rather subtle distinctions. Gunnison's prairie dogs have a different sound for each of coyotes, dogs, hawks and humans. More impressive, they describe what a particular dangerous animal looks like: a human in a blue shirt is announced differently from a human in a yellow shirt. Similarly, meerkats — those charismatic mongooses that stand on their hind legs to scan for predators — give calls that announce both the general type of predator (coming from the sky, coming from the ground) and how close it is — in other words, how urgently everyone should react. Black-capped chickadees — small songbirds that live in North America — have calls that say whether a predator is flying or resting, and if it is resting, how dangerous it is. For example, pygmy owls eat lots of songbirds; horned owls don't. Sure enough, chickadees kick up more of a fuss about perched pygmy owls than they do about perched horned owls.

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