Leland, S. P., West, A. M., Erwin, J. M. et al. 2007. Incorporation of enrichment objects in threat displays by laboratory rhesus macaques (Macaca mulatta). American Journal of Primatology 69(S1), 50. (30th Meeting of the American Society of Primatologists Scientific Program, Abstract #43)

Self-directed aggression in laboratory macaques is commonly considered an abnormal behavioral pattern signaling psychological disturbance, whether it is in the form of self-injurious behavior (SIB) or is just part of a self-directed threat display (SDD). Objects such as Kong® toys have been widely adopted as enrichment and have been observed to be incorporated into threat displays (“toy threats” = TT). Data from a program of behavioral monitoring were examined, and 30 individuals were selected for more intensive observation. Five individuals that had exhibited each of the following patterns were selected: macaques observed to exhibit low (Group 1) or high (Group 2) rates of SDD; macaques observed to exhibit low (Group 3) or high (Group 4) rates of TT; macaques observed to exhibit both TT and SDD (Group 5); and macaques observed to exhibit neither (Group 6). These individuals were then observed for six 5-minute intervals. During this study, those selected for Groups 3 and 4 never exhibited any SDD. Of the subjects selected for Groups 1 and 2, 40% exhibited some TT. Of those selected for Group 5, 60% performed only TT, 20% did both, and 20% did neither. Subjects who had threatened exclusively with toys continued to do so. These results show all transitions in threat displays were from self-directed to object-directed displays, indicating that such enrichment objects may have a therapeutic function.