New York, Sep 24 (IANS): Chimpanzees who are separated from their mothers early in life and raised by humans as pets or performers are likely to show behavioural and social deficiencies as adults, say researchers.

In a year-long study, scientists from Lincoln Park Zoo in Chicago, Illinois, observed 60 chimpanzees to find that experiences during the first four years of life can shape behavioural and welfare outcomes well into adulthood.

Of their study group, over 35 of the chimpanzees were former pets or performers.

"We found 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," explained Steve Ross, director of the Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo.

Specifically, chimpanzees with high human exposure in life tended to engage in less social grooming with their group mates - a critically important behaviour for social bonding in chimpanzees.

"Strikingly, these effects were expressed years, sometimes decades after their lives as pets and performers were over," Ross noted.

"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.

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 cannot fit in with the other chimpanzees," researchers concluded.

The findings of the research project was published in the open access journal PeerJ.