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

In 1986, Samuels and Altmann reported evidence for a hybrid zone between Pa pio anubis and Papio cynocephalus in Amboseli, Kenya, in a baboon populatio n that has been the subject of long-term study since 1971 [Samuels & Altman n, International Journal of Primatology 7:131-138, 1986]. In the current re port we document ongoing patterns of hybridization in Amboseli between anub is and yellow baboons. In July 2000, we exhaustively scored living members of study groups for their degree of hybridity, using seven phenotypic chara cteristics (five in juveniles). We also scored all former members of study groups on the basis of photographic records, field notes, and observer reco llections. 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. Fur ther, the increasing frequency of hybrid phenotypes among animals born into study groups indicates that anubis and hybrid males have successfully repr oduced in study groups. However, hybrid phenotypes and anubis immigrations were limited to groups in the southwestern portion of the Amboseli basin, w ith no hybrids occurring in the six eastern groups. Finally, we present evi dence that anubis and hybrid males in Amboseli exhibit patterns of natal di spersal that are different from those of yellow males in Amboseli: males wi th anubis or hybrid phenotypes were significantly more likely to immigrate as juveniles or young subadults than were yellow males. Am. J. Primatol. 53 :139-154, 2001. (C) 2001 Wiley-Liss, Inc.