SADDLE-BACK TAMARIN (SAGUINUS-FUSCICOLLIS) REPRODUCTIVE STRATEGIES - EVIDENCE FROM A 13-YEAR STUDY OF A MARKED POPULATION

We monitored a population of four to seven groups of individually mark ed saddle-back tamarins (Saguinus fuscicollis; Callitrichidae) at the Cocha Cashu Biological Station in Peru's Manu National Park every year from 1979 through 1992. In this paper we use data on life histories, group compositions, group formations, and dispersal patterns collected during these 13 years to examine the reproductive strategies of males and females. Group compositions and mating patterns were quite variab le in this population, with both monogamy and cooperative polyandry co mmon. In polyandrous groups, two males shared a female's copulations a nd cooperatively cared for her young. Although most groups contained a single breeding female, we recorded four cases in which secondary fem ales successfully reared young. Most young females appeared to wait in their natal groups for the first opportunity to fill a primary breedi ng position in their own or a neighboring group. Females that acquired primary breeding positions maintained those positions for a mean of 3 years. No female was observed to transfer between groups a second tim e. Variation in female lifetime reproductive success was high. Half of the females marked as juveniles never bred; the other half produced a n average of 3.5 young. A paucity of female breeding opportunities may explain the high mortality of females between 2.5 and 4.5 years of ag e and the resulting male-biased adult sex ratio. The majority of group s contained more than one probable male breeder. Polyandrous groups in cluded both related and unrelated males. Behavioral differences betwee n Cocha Cashu tamarins and other studied populations may result from t he pressures of living in an environment inhabited by nine other prima te species and numerous predators. (C) 1996 Wiley-Liss, Inc.