Mild and woolly monkeys.

Mild and Woolly monkeys

The woolly spider monkey, or muriqui, is the largest primate in the Western Hemisphere and ranks among the most endangered primates in the World. Muriquis were once the omnipresent occupants of a forest that stretched along the southeastern coast of Brazil. Much of the forest has been cut for farm and pasture land in the last century, and only 300 to 400 muriquis are known to survive.

In 1982, anthropologist Karen B. Strier of Harvard University began monitoring a group of muriquis in one of the remaining pockets of Brazilian forest. Her research, intended to aid conservation efforts and a planned captive breeding program in Brazil, has uncovered social behavior and organization rarely observed in primate species.

In a study group of 26 individuals continuously observed over 14 months, Strier found an "extraordinary degree' of cooperation and friendship among males. Only the spider monkey and the chimpanzee exhibit comparable levels of "male bonding,' she reports in the most recent ANTHROQUEST. Even more striking, she says, are the low levels of aggression between male muriquis. "Unlike most other primates, indeed, most other vertebrates, male muriquis show no overt competition over access to mates,' explains Strier.

An important reason for this cooperative behavior appears to lie in family ties, she says. Male muriquis did not leave the study group, suggesting thay they mated with the same limited sample of females and, over the generations, had become genetically related to one another. Young females, on the other hand, may tend to leave the group into which they are born; during Strier's observations, two juvenile females immigrated into the study group. Nevertheless, adult males and females travel together in the same group with few signs of conflict, and no adverse effects of inbreeding are currently evident. Cohesive groups, she notes, are better able to compete with other bands of muriqui for the relatively rare fruit species that they prefer to eat.

The study group's pattern of male bonding and female dispersal, a reversal of what is usually observed in primate species, will need to be confirmed in other surviving muriqui groups, says Strier. But knowledge of their strong social relationships will aid efforts to establish captive groups that can reproduce successfully.