Recognizing predators and judging the level of threat that they pose is a crucial skill for many wild animals. Human predators present a particularly interesting challenge, as different groups of humans can represent dramatically different levels of danger to animals living around them. We used playbacks of human voice stimuli to show that elephants can make subtle distinctions between language and voice characteristics to correctly identify the most threatening individuals on the basis of their ethnicity, gender, and age. Our study provides the first detailed assessment of human voice discrimination in a wild population of large-brained, long-lived mammals, and highlights the potential benefits of sophisticated mechanisms for distinguishing different subcategories within a single predator species.

Abstract

Animals can accrue direct fitness benefits by accurately classifying predatory threat according to the species of predator and the magnitude of risk associated with an encounter. Human predators present a particularly interesting cognitive challenge, as it is typically the case that different human subgroups pose radically different levels of danger to animals living around them. Although a number of prey species have proved able to discriminate between certain human categories on the basis of visual and olfactory cues, vocalizations potentially provide a much richer source of information. We now use controlled playback experiments to investigate whether family groups of free-ranging African elephants (Loxodonta africana) in Amboseli National Park, Kenya can use acoustic characteristics of speech to make functionally relevant distinctions between human subcategories differing not only in ethnicity but also in sex and age. Our results demonstrate that elephants can reliably discriminate between two different ethnic groups that differ in the level of threat they represent, significantly increasing their probability of defensive bunching and investigative smelling following playbacks of Maasai voices. Moreover, these responses were specific to the sex and age of Maasai presented, with the voices of Maasai women and boys, subcategories that would generally pose little threat, significantly less likely to produce these behavioral responses. Considering the long history and often pervasive predatory threat associated with humans across the globe, it is likely that abilities to precisely identify dangerous subcategories of humans on the basis of subtle voice characteristics could have been selected for in other cognitively advanced animal species.