PARTNER DIRECTED HAIR-PULLING-AND-EATING IN (MACACA MULATTA). Wisconsin Regional Primate Research Center, Madison, Wisconsin.

Partner directed hair-pulling-and-eating has not yet received attention in the nonhuman primate literature. Hair-pulling-and-eating was recorded 318 times in a heterogeneous troop of 22 healthy rhesus monkeys during 162 hours of observation. The behaviour in question comprises the following sequence:
1) Pulling, with the fingers (33%) or with the teeth (67%), tufts of hair from a partner's coat; the latter shows fear and/or avoidance;
2) chewing and swallowing the indigestible hair.
The majority of 22 animals engaged in this behaviour either by performing it (82%) and/or by serving as recipient for it (99%).
Hair-pulling-and-eating was observed 302 times between animals with clear-cut dominance relationship; it was performed in 95% of cases by dominant and in 5% of cases by subordinate partners.
Young (n=16, 2-7 years old) and old animals (n=7, 15-22 years old) did not differ in regard to dominance rank position (means: 11.7 vs 11.0; p>0.1) but young monkeys performed hair-pulling-and-eating more often than did old ones (means: 19.4 vs 1.2; p<0.05). Young females tended to show this behaviour more frequently than young males (means: 23.3 vs 16.4; p>0.1).
It was concluded that hair-pulling-and-eating is an aggressive behavioural disorder in captive rhesus monkeys, reflecting psychogenic adjustment problems in an unnatural environment.
(Supported by NIH Grant RR-00167).

Reproduced with permission of the Editor of Primate Report.