Male dispersal in patas monkeys (Erythrocebus patas)

Abstract

Potential influences on natal dispersal of wild male patas monkeys ( Erythrocebus patas ) were investigated in Laikipia, Kenya, over a four-year period. Changes in variables were assessed over the six months prior to dispersals. Dispersers left at between 24 and 42 months of age; 60% left at >36 months of age (= the 'large juvenile' age class). Most dispersals coincided with the presence of extra-group males in the study area. Large juvenile males (LJMs) reduced time in proximity to other group members prior to dispersal, driven primarily by less time in proximity to adult females. Aggression involving LJMs was typically rare, mild, and conducted at a distance. Overall aggression bout frequency did not change over time although mild aggressive interactions with the adult male increased in the weeks before LJMs left, suggesting LJMs forestall more serious aggression by leaving. Aggressive interactions with adult females decreased over time. Aggressive bout rates involving other immatures were consistently low. Our data most clearly support the conclusion that LJMs left of their own volition rather than being actively driven out by other group members. Relationships with other males, both inside and outside the natal group, seemed to influence the timing of LJMs' departures.