Polar bears, lions, tigers and other large carnivores that roam over huge territories in the wild become stressed and psychologically scarred when kept in zoos, a study suggests.
Scientists have found a direct correlation between the level of stress an animal suffers in a typical zoo enclosure and the size of its territory in the wild. The biggest, most wide-ranging carnivores suffer the most. Georgia Mason and Ros Clubb, zoologists from the University of Oxford, say their discovery should prompt zoos to reappraise the way they keep big cats, large bears and other crowd pullers.
"Our findings indicate that the keeping of naturally wide-ranging carnivores should either be fundamentally improved or phased out," they write in the journal Nature.
Dr Mason and Dr Clubb investigated 35 animal species by reviewing data on stereotypical behaviour such as pacing up and down and infant mortality published in more than 1,000 scientific papers. They conclude that the animals most likely to suffer problems are also the ones with the biggest natural territories. "Our results show that a particular lifestyle in the wild confers vulnerability to welfare problems in captivity," they say. "Among the carnivores, naturally wide-ranging species show the most evidence of stress and/or psychological dysfunction in captivity, a finding that is a cause for concern, given the difficulties of conserving such species in situ."
Zoos have radically altered the way they keep large carnivores over the past few decades. Most zoos now have bigger and more varied enclosures and have introduced activities that make captivity less monotonous such as variable feeding times. Yet the Oxford study suggests such measures may not be enough for animals that would naturally roam over many thousands of square miles. A typical zoo enclosure for a polar bear, for instance, is about a millionth of the size of its natural territory.
Dr Clubb says she was surprised by the findings because until now the inability to hunt was thought to be the biggest problem for captive carnivores. "Because of this, zoos have concentrated on stimulating hunting-like behaviours to try to improve their welfare," she says. "But our results suggest that it's even more important to give these animals more space, or the day-to-day changes in environment they'd experience if they were ranging naturally."
The Oxford study was criticised yesterday by one of the organisations that helped to fund it. The Federation of Zoos, a scientific wildlife charity, said the findings were "open to misinterpretation".The federation said captive breeding programmes of large carnivores demonstrated that many zoo animals were able to rear their offspring successfully. Miranda Stevenson, the federation's director, said experience had also shown that improving the captive environment of an animal could significantly reduce the level of pacing, an indicator of stress. "Many federation collections keep large carnivores in large and complex enclosures ... and breeding results are excellent," she said.
Infant mortality in the wild among tigers, for instance, was comparable to the level of infant mortality in captive-bred animals. "There is no evidence that neonatal captive infant mortality [in tigers] is higher than that in the wild," Dr Stevenson said.
Dr Mason said the Oxford study did find that infant mortality was higher in wide-ranging species in captivity, suggesting that zoos were not a good place to breed some threatened carnivores. "It's vital to get this right, as these animals are in double jeopardy. Wide-ranging carnivores are particularly hard to conserve in reserves in their natural habitat so it's especially worrying that they are also the most prone to welfare problems in captivity," Dr Mason said.Reuse content