American Journal of Primatology 54:211–221 (2001) © 2001 Wiley-Liss, Inc. Sources of Variability in Numbers of Live Births in Wild Golden Lion Tamarins (Leontopithecus rosalia) KAREN BALES 1 * , MICHELLE O’HERRON 1 , ANDREW J. BAKER 2 , AND JAMES M. DIETZ 1 1 Department of Biology, University of Maryland, College Park, Maryland 2 Philadelphia Zoological Gardens, Philadelphia, Pennsylvania We examined the effects of several variables on the number of live births in multiparous females in a wild population of golden lion tamarins (Leontopithecus rosalia). Independent variables included the number of infants born to a female the previous breeding season, the number of infants weaned the previous breeding season, the female’s age and body mass, the number of adult males and helpers in the group, and the in- breeding coefficient of the offspring. We also tested the hypothesis that trapping and chemical immobilization during pregnancy affected the num- ber of live births. Female body mass was the only statistically significant predictor of the number of live-born infants in the current season when both first and second peaks were included. Characteristics that predicted higher numbers of infants in the first peak of a season were the number of infants born the previous season and the body mass of the female. The greater the number of infants born the previous season, the greater the number of infants born in the first peak of the current season. Factors positively correlated with the number of live births in the second peak within a season included the number of infants born the previous sea- son, as well as the number of available helpers. Due to sample size con- straints, the analysis of litters in the second peak did not include body mass of the female as a variable. Inbreeding and handling did not affect the number of live births. We found no evidence that current reproduc- tion negatively impacts future reproduction in this species. We also found no evidence for an age-related reduction in fertility. Am. J. Primatol. 54:211–221, 2001. © 2001 Wiley-Liss, Inc. Key words: callitrichid; golden lion tamarin; litter size INTRODUCTION There has been extensive study of the maternal characteristics that affect postnatal infant survival in callitrichid primates [Tardif et al., 1986; Pryce et al., 1988, 1993, 1995; Baker & Woods, 1992; French et al., 1996]. Variables that might Contract grant sponsor: NSF; Contract grant sponsor: University of Maryland; Contract grant spon- sor: Sigma Xi; Contract grant sponsor: TransBrasil Airline; Contract grant sponsor: Friends of the National Zoo; Contract grant sponsor: Biology of Small Populations Research Training; Contract grant sponsor: NSF; Contract grant number: SBR-9727687. *Correspondence to: Dr. Karen Bales, Department of Biology, 1204 Biology-Psychology Building, Uni- versity of Maryland, College Park, MD 20742. E-mail: BalesKaren@aol.com Received 5 June 2000; revision accepted 30 April 2001