Hill, A. N., Nash, L. T. 2007. Social and hygienic functions of grooming in captive Papio hamadryas. American Journal of Primatology 69(S1), 107. (30th Meeting of the American Society of Primatologists Scientific Program, Abstract #157)
Social grooming may have both social and hygienic functions. For this analysis, we assume the ‘pick’ grooming method is more effective at cleaning than stroke and social grooming on parts inaccessible to the groomee is hygienic. Grooming was observed in one male and four female hamadryas baboons at the Phoenix Zoo for 60 hours of focal interval sampling (30-sec) recording grooming type (social/autogroom), method (pick/stroke/both), body part (accessible/inaccessible) and partner. Chi-squared tests of association among variables during social grooming were done on the pooled data that corrected for temporal autocorrelation of grooming method. Only 2% of the 1.6 hours of autogrooming was in ‘inaccessible’ body parts while 94% of 14 hours of social grooming were on inaccessible parts, suggesting that both emphasize hygiene. Grooming type was significantly associated with grooming method, with more ‘pick’ and less ‘both’ occurring in self grooming [χ2(2)=47.5, p<0.001] relative to social grooming, suggesting a more mixed hygienic and social function of social grooming. For social grooming, there was no association of method and accessibility [χ2(2)=0.4, p>0.05]. Grooming up the dominance hierarchy greatly exceeded grooming down. Examining bouts of ‘pick’ and ‘stroke’ only, grooming down was 90% pick but grooming up was only 60% pick [χ2(1) =15.96, p<0.001]. This suggests a balance between social and hygienic functions for grooming up while grooming down may be primarily a cleaning ‘service’.