Demography and Dispersal Patterns of a Tamarin Population: Possible Causes of Delayed Breeding

Abstract

We analyze the demography and dispersal patterns of a population of wild saddle-back tamarins (Saguinus fuscicollis) in Peru. Saddle-back tamarins live in small groups with one reproductive female and one or two breeding males. Data on the ages at which females had their first young and the ages at which males and females emigrated from their natal territories show that most animals do not first breed for at least one year past the age of potential sexual maturity. Data on the survival of adults and the lengths of tenure of breeders suggest that breeding vacancies are not frequent. Emigration and survival patterns are not significantly different for the two sexes. We suggest that delayed first breeding may occur in this species for any or all of the following reasons: a shortage of breeding positions, territories, or helpers; the risks of solitary dispersal; and the inclusive-fitness benefits gained from helping. We compare the demographic patterns of S. fuscicollis with those of well-studied cooperatively breeding species and suggest that two preconditions of helping behavior, high costs of infant care and frequent delayed breeding, are quite similar in cooperatively breeding birds and tamarins.