THE NEIGHBOR EFFECT - OTHER GROUPS INFLUENCE INTRAGROUP AGONISTIC BEHAVIOR IN CAPTIVE CHIMPANZEES

While intercommunity interactions are well documented in wild chimpanz ees, the influence of neighboring captive groups on social behavior ha s not been investigated. This study examined the influence of vocaliza tions and noisy displays produced in neighboring groups (i.e., ''neigh bor vocalization'') on intragroup hooting, bluff displays, and agonist ic behavior. Chimpanzees from two broadly differing housing conditions were selected in order to examine the effect of neighboring groups: ' 'Wing Groups'' (those living in indoor/outdoor pens with auditory acce ss to large number of neighboring individuals) and ''Building Groups'' (those housed in one indoor building, able to hear the calls and nois y displays produced by a small number of neighboring individuals occup ying the building). Data were collected on 58 adult and juvenile subje cts living in social groups varying in size from two to 14 individuals . Observation sessions were divided into two categories depending on t he level of neighbor vocalization. Wing Groups showed higher rates of hooting, bluff displays, and agonistic behavior against other group me mbers when levels of neighbor vocalization were high. Building Groups showed the same pattern, with results for bluff displays reaching stat istical significance. This effect was also found through an analysis o f the time periods immediately surrounding incidents of neighbor vocal ization: Hooting and bluff displays were significantly more common aft er than before neighbor vocalizations. In spite of variation between t he two housing conditions with respect to overall levels of neighbor v ocalization, degree of differences between the high and low vocalizati on levels, and methods of data collection, a consistent neighbor effec t was detected. This effect is congruous with behavioral patterns obse rved in the wild, and is therefore considered an expression of species -typical behavior as opposed to an artifact of captivity. These result s are relevant to captive management, and bear on the influence of hou sing condition on psychological well-being. (C) 1996 Wiley-Liss, Inc.