Polar bears, lions, tigers, cheetahs and other wide-ranging carnivores do so poorly in captivity that zoos should either drastically improve their conditions or stop keeping them altogether, biologists from Oxford University report today in the journal Nature.
Zookeepers have long recognized that some species thrive in captivity while others languish. Today the researchers, Dr. Georgia Mason and Dr. Ros Clubb, say the problems -- including high infant mortality and a tendency to pace around and around in the cage -- are directly related to the size of the animal's home range in the wild.
The typical zoo enclosure for a polar bear is one-millionth the size of its home range in the wild, which can reach 31,000 square miles, the authors said. Some captive polar bears spend 25 percent of their day in what scientists call stereotypic pacing, and infant mortality for captive animals is around 65 percent.
The director of the Central Park Zoo in Manhattan, Dr. Dan Wharton, praised the report but said many zoos had already begun work to provide more variety and stimulation for their animals.Continue reading the main story
In 1998, he noted, a redesigned polar bear exhibition opened in Central Park. The exhibit has a gravel pit where the zoo's three bears can dig for food, a snow bank, a redesigned pool and machinery that can turn it into an artificial river.
Last May, the Bronx Zoo opened a new tiger exhibit that incorporates new concepts in architecture and enrichment programs, including a spinning ball scented with various odors.
''There is a heroic effort afoot to create exhibitions so that zoological gardens can present animals with their complete behavioral repertoire,'' said Dr. Wharton, a biologist with the Wildlife Conservation Society, which runs both zoos.
''It's not perfect yet,'' he continued, ''but there is a profession-wide effort to bring everything to bear on it -- architecture and knowledge of the animal's behavior, social structure and habitat.''
Dr. Mason, the Oxford researcher, said animals that had comparatively smaller ranges, including grizzly bears, American mink, red and Arctic foxes, and Eurasian lynxes, seemed to do well in captivity.
The direct relationship of home range size to abnormal behavior and high infant mortality in captivity existed independent of factors like the size and design of the enclosure and feeding schedules, the researchers report. They based their findings on an analysis of some 1,200 journal articles covering four decades of observations of animals in the wild and at 500 zoos worldwide.
It is unclear why natural home-range size is so important.
''It could be that some carnivores roam because they are very sensitive to changing prey densities, or some species find roaming pleasurable, so they roam,'' Dr. Mason said. ''They might be designed in such a way that roaming makes their central nervous system develop properly.''
At the least, zoos must do better at providing mental stimulation and enrichment for their wide-ranging carnivores and other animals to compensate for the loss of room to roam, the Oxford biologists said. Zoos unable to do so should not keep those species, they added.
Dr. Marc Bekoff, an animal ethicist who studies animal behavior patterns at the University of Colorado, called the new study ''one of the most important papers I've seen on carnivores' well-being in captivity,'' and added, ''Zookeepers will have to reckon with the results.''
But Dr. Michael Hutchins, director of conservation science for the American Zoo and Aquarium Association, which accredits American zoos, said he found ''broad generalizations'' and ''real weaknesses'' in the study. He noted that it did not list all the species in question.
Other studies have shown that the three factors most important in causing stress were a lack of variety in diet, lack of barriers that allow an animal to hide from view, and inconsistency in its relationship with its caretakers, Dr. Hutchins said.
A number of American zoos have already built large, naturalistic enclosures that provide stimulation for the animals, he said. They have also begun feeding large carnivores whole carcasses so they can engage in more natural feeding behavior and encouraging caretakers to be more consistent in their treatment of the animals.
''I haven't seen any evidence of pacing at these facilities,'' Dr. Hutchins said.
Dr. Mason praised efforts that successfully compensate for the loss of a large natural home range. ''That's what zoos should be aiming for,'' she said.Continue reading the main story