Informative breath: olfactory cues sought during social foraging among Old World monkeys (Mandrillus sphinx, M. Leucophaeus, and Papio anubis).

Sociality provides a unique opportunity for animals to acquire information and learn from others. Especially during foraging, where trial-and-error food selection might be fatal, conspecifics could act as valuable sources of information. During a six-year study across captive, semifree ranging, and wild Old World monkeys, I investigated whether individuals garnered olfactory-based information from their group mates that could guide their feeding decisions. Each of three study species [mandrills (Mandrillus sphinx), drills (M. leucophaeus), and olive baboons (Papio anubis)] performed a prominent muzzle-muzzle behavior, potentially enabling individuals to smell others' mouths and determine via olfaction what foods their conspecifics had chosen. This muzzle-muzzle behavior (1) was preferentially directed by naïve, younger individuals toward more experienced, older individuals, (2) occurred specifically while recipients were chewing and hence emitting the most potent chemical cues, (3) was typically followed by the actor consuming the very same food type the recipient had been eating, (4) was elicited most often in response to experiments involving novel foods, and (5) occurred less frequently as initially novel foods became more familiar. In contrast to this evidence for information acquisition, there was little support for previous proposals suggesting that muzzle-muzzle functions as a social display. Instead, the omnivorous diets and intensely social lifestyles of mandrills, drills, and baboons, may have each favored a convergent form of information acquisition: seeking out the breath of knowledgeable conspecifics to help decide what foods are safe to eat.