Many chimpanzees housed in zoos show abnormal behavior that suggest mental illness, according to a new PLoS One study.
The documented behaviors, which included self-mutilation, repetitive rocking, and consumption of feces, are symptoms of compromised mental health in humans, and are not seen in wild chimpanzees, the authors say. The study found that even chimps at very well regarded zoos displayed the disturbing behaviors.
"Absolutely abnormal behavior and possible mental health issues are most commonly associated with lab chimps," co-author Nicholas Newton-Fisher told Discovery News. "This is one of the reasons we were surprised to see the levels of abnormal behavior that we did -- in chimpanzees living in good zoos."
"We conclude that the chimpanzee mind might have difficulties dealing with captivity," added Newton-Fisher, a primate behavioral ecologist at the University of Kent's School of Anthropology & Conservation.
He and co-author Lucy Birkett used both direct observations and published sources to document the behaviors of 40 chimpanzees at six zoos in the U.S. and the U.K. The collected data, covering a two-year period, was then compared to observations made of wild chimpanzees, such as 1023 hours of documentation on wild chimps in Uganda.
All 40 zoo chimps displayed some form of abnormal behavior, according to the researchers. The chimps would poke at their own eyes and other body parts, bang themselves against surfaces, pull out their hair, pace, drink urine, and do other things not associated with wild chimpanzee populations.
All of the study chimps were "kept in what are often considered the best captive conditions," Newton-Fisher said, explaining that the primates are "socially housed, fed a varied diet according to a varied schedule, provided with environmental enrichment" and more.
While other studies demonstrate that improving the environment for captive chimpanzees can help to reduce behavioral concerns, zoo confinement itself appears to be inherently problematic for these intelligent animals.
"I have lived and worked in East Africa, following free-living chimpanzees through the forest on a daily basis," said Newton-Fisher. "With that experience, personally I find it hard seeing chimpanzees in zoos."
But he admits that zoos often provide a sanctuary for chimpanzees acquired from sources such as laboratories and the pet trade. It would be difficult to release these human-raised animals back into the wild.
"I would rather see those chimpanzees kept in the best conditions we can manage rather than see them euthanized," he said. "In some rare circumstances, perhaps from sanctuaries from within habitat countries, it may be possible to release chimpanzees into the wild, but I think for many captive chimpanzees this is not a sensible option."
A recent study also found that zoo visits boost a child's science and conservation education more than books or classroom teaching alone. Over 50 percent of all school children aged between 7 and 14 showed improvements in their knowledge of animals, habitat and conservation after just a single zoo visit.
"The research clearly shows the valuable role that zoos can play in children's science learning," said Eric Jensen, a professor of sociology at the University of Warwick who urges families to visit zoos over the long holiday weekend and during other free times.
Great Ape Trust scientist Sue Savage-Rumbaugh, however, suggests that zoos need to pay more attention to the mental health of their chimp charges.
"Efforts to improve captive welfare in apes have focused upon the need for social companions, adequate cage space, fresh fruits and vegetables, variety in the diet, and some type of enrichment," Savage-Rumbaugh explained.