Relationship between age and activity varies by sex in titi monkeys (Callicebus cupreus)

Motor activity increases during development and typically peaks before reproductive maturity. Males may become more active than do females, and this sex difference in activity may be a mechanism contributing to sex-biased dispersal. The generality of the link between sex differences in activity and sex differences in dispersal would be strengthened with evidence of greater female, as compared to male, activity during development in a species with a female bias in dispersal. Titi monkeys are a good model for such an investigation because subadult females leave their natal group at an earlier age than do subadult males. This study examines whether developing female titi monkeys become more active with age than do developing male titi monkeys. Locomotor activity of 13 female and 8 male captive titi monkeys was measured as they matured from initial ambulatory independence (6 months of age) to reproductive maturity (24 months). Increased activity of females was associated most strongly with increasing age. Increased activity of males, however, was associated most strongly with repeated testing. Compared to maturing males, greater activity of maturing females may underlie the earlier dispersal of female titi monkeys that has been reported.