WHY SHOULD AN AGED MALE BABOON EVER TRANSFER TROOPS

Dispersals by subadult or adult male baboons are common. In contrast, the occasional transfer of aged baboons is puzzling, given the physica l dangers of transfer and the cognitive demands of mastering the ecolo gical and social rules of a new troop. The present data suggest a poss ible explanation for such transfers in a study of two troops of olive baboons (Papio anubis) in Kenya. Aged males who remained in the troop in which they had been dominant were subjected to significantly higher rates of approach-avoid interactions by the current high-ranking coho rt (i.e., the individuals they had dominated years past) when compared to males who had transferred into the troop in their old age. Thus, t ransfer in old age offers the advantage of relative anonymity. Of the 14 males who progressed into older adulthood in the same troop in whic h they were in their prime, seven ultimately transferred to a differen t troop. The seven who remained and the seven who transferred did not differ in the rate at which they were subjected to approach-avoid inte ractions. However, those who remained had significantly higher rates o f various affiliative behaviors (copulations, consortships, grooming a nd contact with females, and positive interactions with infants). Thus , amid the disadvantages of an old age spent in the troop in which a m ale baboon was in his prime, a high degree of social affiliation might constitute a sufficient disincentive against transferring. (C) 1996 W iley-Liss, Inc.