Chapter 8 The Reproductive Ecology of South American Primates: Ecological Adaptations in Ovulation and Conception Toni E. Ziegler, Karen B. Strier, and Sarie Van Belle 8.1 Introduction The process of ovulation does not necessarily end in conception and production of offspring. Although some South American primates, such as common marmosets (Callithrix jacchus), regularly conceive following ovulation, other species, such as northern muriquis (Brachyteles hypoxanthus), are more likely to experience multiple ovarian cycles prior to conception. The development of non-invasive fecal collection and analyses techniques permit us to investigate the factors that affect the variation in conception processes of wild primates. Insights into the reproductive endocrinology of South American primates were previously limited to specialized studies of captive species such as squirrel mon- keys, marmosets and tamarins, capuchin monkeys and owl monkeys (Hearn 1983). More recently, researchers studying wild populations have provided new informa- tion on their reproductive biology, which allows us to understand their reproductive strategies from a more ecological perspective. Factors such as food quality, group composition, rainfall, and other seasonal environmental conditions can influence the fertility of males or females within a species. In addition, many aspects of the ovar- ian cycles and endocrine metabolism of platyrrhines (New World monkeys) differ from those of catarrhines (Old World monkeys, apes and humans). This chapter will examine the variables affecting female fertility and the timing of ovulation and conception in South American primates. 8.1.1 The Primate Ovulatory Cycle Unlike other mammals, anthropoid primates have ovarian cycles that are not generally considered as estrous cycles. Mating activity is not restricted to the T.E. Ziegler (B) Wisconsin National Primate Research Center, Department of Psychology, University of Wisconsin-Madison, Madison, WI 53715, USA e-mail: Ziegler@primate.wisc.edu P.A. Garber et al. (eds.), South American Primates, Developments in Primatology: Progress and Prospects, DOI 10.1007/978-0-387-78705-3 8, C  Springer Science+Business Media, LLC 2009 191