CREDIT: DANA PFEFFERLE
Many primates spend up to a fifth of their time going through one another's fur. This grooming behavior helps keep them healthy both physically and mentally--relaxing the animals and helping cement social relationships. Now a study of the so-called Barbary apes finds that the stress reduction benefits the groomers even more than the groomed.
A team led by primatologists Ann MacLarnon and Stuart Semple of Roehampton University in London followed 11 female macaques on the Rock of Gibraltar over 2 months, recording grooming behavior and collecting feces to analyze the stress hormone cortisol. The animals who tended others the most--both in terms of time spent and number of animals groomed--had the lowest cortisol levels, they report in the 7 June issue of Biology Letters. The busiest groomer, who averaged almost 16 minutes per hour, had half the cortisol levels of one that only spent a few minutes at it.
For those on the receiving end, there was no correlation between cortisol levels and grooming. The team suggests that more active groomers are less stressed because they have stronger social support networks. Psychologist Robin Dunbar of the University of Liverpool in the U.K. says, "This is a very timely study because we really don't understand what makes grooming so worthwhile for groomers."
