White-faced capuchins, like humans, have large brains and long lives. They have the largest brains for their body size of any nonhuman primate. They can live to be over 30 years old in the wild, and into their 50s in captivity. A female capuchin is about the same size of a house cat, but whereas a cat produces her first litter of kittens when she’s less than a year old, a capuchin gives birth for the first time at age 6 years, and produces only one baby at a time, every two years or so. Females remain with their female relatives their entire lives, helping one another by caring for and even nursing the offspring of their relatives. However, males generally leave their birth troop when they’re about 7 years old, and may switch groups periodically after that. Sometimes males make these moves on their own, but in about 80% of cases, they make the move to a new group with one or more other males, who are usually their relatives.
The alpha, or highest-ranking, male in the group is the father of almost all of the offspring, unless he has been in the group long enough to have daughters who are old enough to produce offspring themselves. When that happens, his daughters’ children are fathered by the subordinate adult males, who have been helping the alpha male defend the group from intruder males and predators.
In 2001, the Lomas Barbudal Monkey Project began an in-depth study to follow, from birth, the lives of 50 monkeys born into three different troops. Our goal was to see how these animals’ foraging skills and social strategies were affected by a variety of factors, including basic personality traits (like impulsivity and sociability), the composition of their childhood group (for example, how may playmates of the same and opposite sex were available?), ecological factors (e.g. the amount of rainfall or fire damage to their habitat) and opportunities to observe complex food-processing techniques in action. Ultimately, by following these individuals for their entire lives, we hope to discover how all of these factors affect monkeys’ reproductive success.
Some of the specific questions that we're investigating include:
- How do sex differences in behavior emerge during childhood and adolescence?
- How do young males decide when to leave their birth group, whom to accompany in this endeavor, and which new group to try to join?
- Do young capuchins treat their paternal kin (that is, those who have the same father but different mothers) differently from non-kin?
- What factors contribute to first-time mothers' parenting styles?
- How changeable is individual personality over the course of development, and how do personality and experience interact to influence individuals' social strategies?