Research institutions have recently come under attack for trauma in their rhesus monkeys (Macaca mulatta). The fighting is blamed on crowded housing conditions. The literature, however, suggest a more complex relation between space and aggression. A comparison between free-ranging temple monkeys in Kathmandu, monkeys in a large corral, and caged monkeys with a relatively high population density yields and average rate of between 1.6 and 2.2 aggressive acts performed per adult female per hour. In addition to this small variability, the highest rate is not found under the most crowded condition. For males, the variation is greater, with by the highest aggression rate in the free-ranging population. Nonaggressive behavior can also be affected by spatial conditions. Patterns which increase under crowding (e.g. grooming) may serve to regulate social tensions. Buffering mechanisms are expected to be particularly well- developed in groups of monkeys with a long history of captive housing. The proposed research aims at an investigation of 1) the relation between population density and the rate of aggressive behavior in well-established, provisioned rhesus monkey groups under a wide range of spatial conditions, and 2) the role of affiliative behavior in social adjustment to environmental conditions. For this purpose, rhesus monkeys will be observed in social groups housed in laboratory cages, in medium to large pens, and in spacious corrals at two Regional Primate Research Centers. These observations will be compared with those on Free-ranging, provisioned groups of the same species. Except for one experimental manipulation, the study will be of an observational nature. Subjects will be observed in the environment in which they have lived for many years, surrounded by familiar individuals. The social behavior of one individual at a time will be recorded on a portable computer during ten-minute intervals. Besides aggressive acts of various intensities, records will include the context of aggression, the direction and duration of affiliative behavior, and the probability of inter-opponent reunion following an aggressive incident. Over a 3 year period data will be collected on 42 adult males and 150 adult females. The proposed experiment consists of confining an entire monkey group for eight hours to a familiar space that is smaller than their normal enclosure. Such acute crowding is expected to have a greater effect on aggression than chronic crowding. The study is intended to illuminate some of the pros and cons of social housing; an important issue in the ongoing debate about laboratory animal well-being.
