Demographic and descriptive studies at La Parguera, Puerto Rico.

The La Parguera facility was established in part to contrast the social behavior of free-ranging groups with that in enclosures, as well as to compare the seasonal events linked to reproduction with those at Cayo Santiago. Onset of breeding was correlated with onset of the rainy season at both sites. Male rank in new social groups was correlated with seniority, and males often joined groups containing older brothers. Dominant males had little influence on group movements or group rank. Maternal rank influenced the likelihood that male offspring would survive and reproduce: sons of dominant females had higher survival. High-ranking females and high-ranking groups produced more sons than daughters at birth. Observational techniques employed at La Parguera demonstrated the biases of using ad lib. field notes and the need to correct for observability of individuals as a function of their age, sex, and social rank. Although social behavior was qualitatively similar in enclosed and free-ranging groups, significant quantitative differences existed. During its 18 years of existence the La Parguera colony proved to be a fertile site for both descriptive and experimental studies. In this paper we briefly review behavioral and ecological findings from the free-ranging population, review the demographic analysis of a cohort of monkeys born early in the colony's history and followed until death, and, finally, focus on methodology in the study of free-ranging primates.