Peer separation in infant chimpanzees, a pilot study

Abstract

Seven nursery reared chimpanzees (Pan troglodytes), 7.5 to 10.5 months of age, were studied to determine the effects of a short period of separation from their peers on behavior and heart rate. The chimpanzees were separated from their mothers at birth, and reared in the nursery in a group living environment. The experiment encompassed a 13-day period, including 4 days of normative baseline, 5 days during which three of the infants were separated and housed in isolation while the other four controls remained together, and 4 days in which all of the animals were reunited. Six quantified behavioral observations and five heart rate measurements were obtained daily. Following separation, the isolated infants were behaviorally agitated, and exhibited increases in vocalizations, rocking and self-clasp behaviors, as well as changes in facial expression including cry face, whimper face and pout face. Time spent locomoting decreased in all seven animals during the separation period. Agitated behavior in the separated and isolated infants alternated with stationary withdrawn behavior. Individual differences were prominent. Heart rate was notable by the generally poorly developed circadian rhythmicity throughout the 13 day period; significant HR changes did not appear otherwise associated with separation. Day three of separation appeared to represent a point of transition with stereotyped motor behaviors developing in the three isolated infants and in one control infant.