Dispersal, group formation and kinship in the black-faced lion tamarin (Leontopithecus caissara).

We report on (i) new group formation, (ii) sex differences in dispersal and (iii) dispersal distance over 6 years for 3 social groups of the black-faced lion tamarin (Leontopithecus caissara) in the vicinity of Ariri, São Paulo state, Brazil. The groups were: Bina (monitored for 74 months), BM5 (52 months) and Teca (13 months). Each group was censused once a week and monitored for 3 days each month. Mating opportunities were found to be the incentive for young adult black-faced lion tamarins to either disperse or remain in their kin group. Young adults show delayed dispersal that is related to the cooperative breeding system characteristic of the Callitrichidae and to a low population density which hinders the formation of new breeding pairs. Our findings suggest that in L. caissara (i) both sexes disperse, (ii) successful immigration is related to breeding opportunities in an existing group, (iii) female immigration motivates male emigration and the formation of new groups, and (iv) emigrants tend to form new groups close to their natal groups. These patterns of dispersal and formation of new groups are efficient because the species has been able to avoid loss of genetic diversity despite their small population size.