Baboons eavesdrop to deduce mating opportunities

Many animals appear to monitor changes in other individuals’ dominance ranks and social relationships and to track changes in them. However, it is not known whether they also track changes in very transient relationships. Rapid recognition of a temporary separation between a dominant male and a sexually receptive female, for example, should be adaptive in species where subordinate males use opportunistic strategies to achieve mating success. Dominant male baboons (Papio hamadryas ursinus) form sexual consortships with oestrous females that are characterized by mate guarding and close proximity. To assess whether subordinate males track temporary changes in the status of other males’ consortships, we conducted playback experiments using a two-speaker paradigm. In the test condition, subjects heard the consort male’s grunts played from one speaker and his consort female’s copulation call played from a speaker approximately 40 m away. This sequence suggested that the male and female had temporarily separated and that the female was mating with another male. In a control trial, subjects heard another dominant male’s grunts played from one speaker and the female’s copulation call played from the other. In a second control trial, conducted within 24 h after the consortship had ended, subjects again heard the consort male’s grunt and the female’s copulation call played from separate speakers. As predicted, subjects responded strongly only in the test condition. Eavesdropping upon the temporal and spatial juxtaposition of other individuals’ vocalizations may be one strategy by which male baboons achieve sneaky matings.