Lack of pubertal influences on female dispersal in muriqui monkeys, Brachyteles arachnoides

The hormonal mediation of dispersal in female mammals is poorly understood, in part because of the difficulties of detecting the onset of ovarian cycling and puberty in dispersing individuals. We used noninvasive methods of faecal steroid assays to determine the timing of dispersal relative to puberty and ovarian cycling in wild female muriqui monkeys, a species in which males are philopatric and nearly all females transfer from their natal groups. Natal females had a mean+/-SE age of 73.4+/-7.2 months (N=18) at the time of their transfers. Intergroup transfers occurred when one or more sexually active adult females were present, but did not show any seasonal patterns. Faecal progesterone and oestradiol profiles from nine natal females prior to transfer and four non-natal females that transferred into our study group demonstrate unequivocally that dispersal occurs prior to puberty in this species. All females showed baseline oestradiol levels and low progesterone levels compared with cycling adult females. Immigrants were first observed to copulate at 11.2+/-2.2 months of age (N=4), prior to the onset of normal ovarian cycles, and gave birth to their first offspring at 33.8+/-7.3 months (N=4) after transferring. Mean cortisol levels did not differ between natal emigrants or recent immigrants, and were within the range of those of adult males during the nonbreeding season in 10 of the 11 prepubertal females sampled. These results indicate that female dispersal is not triggered by activational hormones associated with puberty or escape from reproductive suppression in this species. Copyright 2000 The Association for the Study of Animal Behaviour.