The continued destruction of the coastal and tropical forest in South and Central America threatens the survival of natural animal populations, including the callitrichid primates (tamarins and marmosets). While the golden lion tamarins are considered an endangered species, through a highly successful breeding program at the University of Nebraska under the auspices of the National Zoological Park, these primates are being bred in captivity and a small group of six have recently been reintroduced into forests of Brazil. Their survival as a species, however, depends extensively on understanding how their reproduction is synchronized to lead to a greater likelihood of fertilization. Dr. French will investigate the complex interplay between internal physiological factors and external social and environmental factors in gold lion tamarins. Unlike Old World primates and apes, the callitrichid primates are monogamous and thus, develop a close and long-lasting association, or pair- bond, between a breeding male and female. Dr. French will use noninvasive data collection techniques for both hormone samples and behavioral measurements to compare the degree to which social factors influence hormonal regulation of reproduction. His findings will be compared with the results obtained in similarly conducted studies in which Old World non-monogamous primate species have been used. This work will contribute to our understanding of the role of hormonal and social influences on reproductive behavior in golden lion tamarins as well as other New World primates of which many are considered threatened or endangered species. Furthermore, the results will significantly enhance the captive breeding programs of endangered species and thus, contribute to the preservation of these small South American primates.