Although the immediate welfare consequences of removing infant chimpanzees from their mothers are well documented, little is known about the long-term impacts of this type of early life experience. In a year-long study, scientists from Lincoln Park Zoon observed 60 chimpanzees and concluded that those who were removed from their mothers early in life and raised by humans as pets or performers are likely to show behavioral and social deficiencies as adults.
The multi-institutional research project, published today in the open-access journal PeerJ, was led by Steve Ross, PhD, director of the Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo. Over the course of 14 months the researchers studied 60 chimpanzees with a range of personal histories, all of whom were living in a variety of zoos accredited by the Association of Zoos and Aquariums (AZA) and sanctuaries participating in the North American Primate Sanctuary Alliance (NAPSA). Of their study group, over 35 of the chimpanzees were former pets or performers.
The results suggest that chimpanzees raised primarily around humans with less experience around their own species during the first four years of life, tend to show reduced social competencies as adults than those with more natural early histories. Specifically, chimpanzees with high human exposure in life tended to engage in less social grooming with their groupmates, a critically important behavior for social bonding in chimpanzees. Strikingly, these effects were expressed years, sometimes decades after their lives as pets and performers were over.
"Unusually for a study on this topic, we looked at the degree of human and chimpanzee exposure on individual chimpanzees along a continuum," explained Ross. "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."
The study follows decades of research that has demonstrated the importance of maternal care for primates, but is among the first attempts at a more holistic approach to understanding not only how both human and chimpanzee exposure can affect behavioral development, but how those effects are expressed much later in life.
Zoos and sanctuaries are often the recipients of ex-pet and ex-performer chimpanzees when their owners deem them too difficult to provide care. Ross, who is also the founder of Lincoln Park Zoo's Project ChimpCARE, has helped facilitate the transfer of more than 30 chimpanzees from private homes and entertainment complexes to more species appropriate habitats and social groups within accredited zoos and sanctuaries since 2009.
"One of the startling aspects of these findings is that these behavioral effects are so long-lasting," said Ross. "Chimpanzees which have found new homes in accredited zoos and good sanctuaries continue to demonstrate behavioral 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."
Despite the fact that chimpanzees are an endangered species, and can pose health and public safety risks, it remains legal in most of the United States to own a pet chimpanzee. Ross expresses hope that these findings will add to growing evidence against such practices.
"Chimpanzees are incredibly intelligent and sensitive animals," he said. "Denying them access to members of their own species, during the critical infanthood period, results in behavioral outcomes that last a lifetime. Even with the best possible care as adults, they often can't fit in with the other chimpanzees."