• prehensile tail;
  • ontogeny;
  • Alouatta;
  • Cebus

A study of the platyrrhine prehensile tail provides an opportunity to better understand how ecological and biomechanical factors affect the ability of primates to distribute mass across many different kinds of arboreal supports. Young individuals experience ontogenetic changes in body mass, limb proportions, and motor skills that are likely to exert a strong influence on foraging strategies, social behaviors, support use, and associated prehensile-tail use. In this research, I examine ontogenetic patterns of prehensile-tail use in Cebus capucinus and Alouatta palliata. I collected behavioral data on activity, positional context, support size, and prehensile-tail use in five age categories of white-faced capuchins and mantled howlers during a 12-month period at Estación Biológica La Suerte in northeastern Costa Rica. Infant and juvenile howlers and capuchins were found to use their prehensile tails significantly more often than adults during feeding, foraging, and social behavior. Prehensile-tail use did not show predictable increases during growth. In both species, adults used their prehensile tails in mass-bearing modes significantly less often than juveniles. Despite differences in tail anatomy in Cebus and Alouatta, prehensile-tail use was observed to follow an increasing trajectory from infancy, peaking during juvenescence, and then decreasing in older juveniles and adults. In both species, it appeared that adult patterns of prehensile-tail use reflected the demands placed on young juveniles. Am. J. Primatol. 74:770-782, 2012. © 2012 Wiley Periodicals, Inc.