Behavioral correlates of dispersal in female muriquis (Brachyteles arachnoides)

We documented four adolescent female transfers-two emigrations, two immigrations-during a 12-month study from August 1994 to July 1995 on one group of muriquis (Brachyteles arachnoides) at Estacoa Biologica de Caratinga in Minas Gerais, Brazil. Intergroup transfers occurred throughout the year independent of season. A total of 613 focal samples of 10-min duration conducted on six adolescent females (5-9 years of age) revealed significant differences in the behavior of migrant versus natal resident females. During the seasons encompassing their respective group transfers, both emigrants and immigrants devoted more of their time to resting than resident females belonging to the same age cohorts did. Time spent feeding on mature fruit was higher for one emigrant and lower for both immigrants compared to the two resident females. Emigrant females had fewer neighbors within a I-m radius than resident females did, whereas immigrant females were within a I-m radius of adult females and within a 5-m radios of adult males more often than resident adolescent females were. Adolescent females were displaced on 26 occasions. Displacements occurred mainly during the dry sea sons (n = 21) and mainly at food sources (n = 21). Using the number of focal samples conducted on each female as an estimate of observation time, immigrant females were displaced at twice the rate of residents. However, like other behavioral differences detected between resident and migrant adolescent females, differences in individual displacement rates were evident only during the season in which each of the immigrants joined the group. Collectively, our findings imply that female intergroup transfer in this population involves relatively mild, short-term costs.