Caged in. Polar bears are the animals that do worst in captivity.

Zoo Carnivores Need More Space

Carnivores such as polar bears, tigers, cheetahs, and lions are especially poorly suited for life in a zoo, according to a new study. The more an animal roams in the wild, the researchers found, the worse it fares in captivity.

Some animals thrive in captivity, but other species die young, don't reproduce, and show bizarre, repetitive behaviors. Captive polar bears, for instance, spend much of their day pacing back and forth, and clouded leopards pluck their fur out. Researchers believe these animals suffer because they're too confined to carry out their normal routines. Behavioral biologists Georgia Mason and Ros Clubb of the University of Oxford, U.K., reasoned that how well animals adapt to zoo life might vary with how they live in the wild.

The researchers examined more than 1200 studies on 35 species of carnivores. In the 2 October issue of Nature, they report that the larger the home range, the higher the frequency of pacing and the more infant deaths in captivity. Among the worst off were polar bears, which have a home range of 1000 square kilometers or more--about 1 million times bigger than their average enclosure, Mason says. They paced about 25% of the day and had an infant mortality rate of 65%. In contrast, brown bears, with a minimum range of 0.5 square kilometers, spent only 10% of the day pacing and had negligible infant mortality. Foraging time and general activity in the wild did not appear to affect pacing or infant mortality. Neither did time spent hunting, which Mason and Clubb had predicted would be the biggest problem for zoo carnivores.

Mason suggests that bigger enclosures might improve the welfare of wide ranging animals, but she also says that zoos should consider housing fewer of these animals and more of the animals that do well in captivity.

This is the "most extensive" work on the well-being of captive carnivores, says behavioral ecologist Marc Bekoff of the University of Colorado, Boulder. The results are not surprising, says Bekoff, but it's the first rigorous scientific study to demonstrate that "wide-ranging animals don't like their freedom compromised." But Michael Hutchins, the director of conservation and science at the American Zoo and Aquarium Association, finds the methodology "highly simplistic" because it fails to address varying zoo conditions and management that can greatly affect animal welfare.

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Georgia Mason
Marc Bekoff
Michael Hutchins