Chimpanzees that are raised as pets or performers from an early age face behavioural problems that last a lifetime, researchers have found.
In the US, it is legal in most states to own chimpanzees as pets, even though they are an endangered species and can pose a huge threat to health and public safety. It is estimated that over 700 chimpanzees are kept as pets in the US.
Experts have long known removing a chimpanzee from its mother early on has an adverse impact, however less is known of the long-term effects.
Researchers at the Lincoln Park Zoo looked 60 chimpanzees to assess the long-term impacts of separation from an early age and found it results in behavioural and social deficiencies that last well into adulthood.
Published in the journal PeerJ, the team spent 14 months studying animals with a range of personal histories in zoos across North America. Of these, 35 were either pets or performers.
Steve Ross, director of the Fisher Centre for the Study and Conservation of Apes at Lincoln Park Zoo, said: "Unusually for a study on this topic, we looked at the degree of human and chimpanzee exposure on individual chimpanzees along a continuum.
"This showed that those chimpanzees with more atypical beginnings to their lives, spending much more time with humans than with their own species, tended to behave differently than those that stayed with their family through infanthood."
Chimpanzees with high human exposure spent less time social grooming with other chimpanzees – sometimes for decades after being reintroduced to their own species.
"One of the startling aspects of these findings is that these behavioural effects are so long-lasting," he said. "Chimpanzees which have found new homes in accredited zoos and good sanctuaries continue to demonstrate behavioural patterns that differentiate themselves from more appropriately-reared individuals. As a result, the process of integrating them with other chimpanzees can be challenging, stressful and even dangerous at times."
Ross warned that their findings should encourage people to stop keeping chimpanzees as pets due to the detrimental effect it has on the animals throughout their lives.
"Chimpanzees are incredibly intelligent and sensitive animals. Denying them access to members of their own species, during the critical infanthood period, results in behavioural outcomes that last a lifetime. Even with the best possible care as adults, they often can't fit in with the other chimpanzees."