Bonobos, Overgrooming and Captivity
Grooming is a natural behavior among all kinds of animals, both wild and in captivity. While grooming can serve a variety of functions, both physical and social, “overgrooming” (sometimes referred to as “hair-plucking”) most often occurs in captivity and other stressful situations. Overgrooming has been observed in various ways in captive primates, but many studies have relied on survey research. In this study, researchers directly observed a group of captive bonobos at Columbus Zoo and Aquarium in Ohio, “to assess the prevalence and distribution of hair plucking” and to see how variables like “age, sex, and dominance rank” might have an effect on it.
What they found was that overgrooming was present in this group of bonobos, but it was “not uniformly distributed.” It was a common behavior, present in about 21% of all bouts of grooming. Interestingly, wild-born individuals “were never observed to hair pluck and were rarely the recipients of plucking behavior.” This was despite the fact that wild-born individuals were housed with bonobos that frequently overgroom and so had observed the behavior. Otherwise, they found that adolescent males plucked more frequently than adult males, but there was not a significant difference between males and females. The researchers also found no link between dominance rank and hair plucking. In general, hair plucking was observed more often inside than outside.
Although the researchers note that overgrooming doesn’t seem to result in any “immediate negative health consequences” for the captive bonobos, it does indicate something may be wrong psychologically. While these researchers think that “an ape’s appearance and the response of zoo visitors is a separate but related issue,” this is something that will be very relevant for advocates. The study shows that captive bonobos exhibit overgrooming in a way that wild-born bonobos don’t, and that difference itself is worth investigating further.