Murder in the Troop
Communication Skills: Vocal Communication

Chacma baboons draw upon a rich repertoire of vocal signals to express themselves. Adult males may assert their dominance in a troop by emitting relatively soft, but threatening “uh huh” sounds that are referred to by primatologists as “grunts.” Grunting commonly precedes a “two-phase bark,” which is a deep, loud “wa-hoo” call, emitted at intervals of 2 to 5 seconds. This call is frequently directed in aggression toward other males or an approaching predator.

But antagonism on the part of a male may evoke the equally powerful vocal response known as “screeching.” In a series of high-pitched screams, male and female baboons of all ages use this vocal tactic in their defense, as it appears to inhibit the hostile behavior of the aggressor.

When retreating from a threatening animal, subadult and adult baboons may emit a short, sharp “yakking” call, while infants and juveniles produce a chirplike “clicking.” These sounds are often coupled with a “fear-grimace” in which the animal retracts its lips and exposes its clenched teeth. This display serves as a pacifying gesture and is used to avert an aggressive encounter. Infants in distress may also emit a cry known as an “ick-ooer,” a two-phased call made through pursed lips.

In the case of immediate danger, all members in a troop, with the exception of the adult males, engage in a “shrill bark” — an explosive, single, sharp cry of alarm that alerts troop-mates to flee. Higher in pitch than the shrill bark is the “doglike bark,” sent out by subadult and adult baboons when members are thought to be separated from the troop.

But not all calls are designed to communicate aggression, fear, or danger. The animals articulate friendly intentions through low, soft “rhythmic grunts,” interpreted as an amiable greeting when one individual approaches another. Juveniles at play are often heard emitting nasal “chattering,” which involves rapid murmurs that signal, at least for the moment, all is well in their world.

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