Immigration and hybridization patterns of yellow and anubis baboons in and around Amboseli, Kenya.

In 1986, Samuels and Altmann reported evidence for a hybrid zone between Papio anubis and Papio cynocephalus in Amboseli, Kenya, in a baboon population that has been the subject of long-term study since 1971 [Samuels & Altmann, International Journal of Primatology 7:131-138, 1986]. In the current report we document ongoing patterns of hybridization in Amboseli between anubis and yellow baboons. In July 2000, we exhaustively scored living members of study groups for their degree of hybridity, using seven phenotypic characteristics (five in juveniles). We also scored all former members of study groups on the basis of photographic records, field notes, and observer recollections. A total of five anubis males and 11 males with hybrid phenotypes have immigrated into study groups over the course of the long-term study, and immigrations by hybrid males have increased in frequency over time. Further, the increasing frequency of hybrid phenotypes among animals born into study groups indicates that anubis and hybrid males have successfully reproduced in study groups. However, hybrid phenotypes and anubis immigrations were limited to groups in the southwestern portion of the Amboseli basin, with no hybrids occurring in the six eastern groups. Finally, we present evidence that anubis and hybrid males in Amboseli exhibit patterns of natal dispersal that are different from those of yellow males in Amboseli: males with anubis or hybrid phenotypes were significantly more likely to immigrate as juveniles or young subadults than were yellow males.