Roving animals don’t thrive in zoos, study finds

Animals that roam widely in nature fare poorly when they are fenced in at zoos, according to a study that calls for an overhaul of the way such beasts are kept.

In captivity, wide-ranging species such as polar bears and lions have a higher infant mortality rate and are more likely to pace back and forth out of boredom than other zoo animals, British researchers found in an analysis of 40 years of data.

Most zoos around the world need to build larger, more complex exhibits for roving animals, said Georgia Mason, an Oxford University zoologist and the study’s lead author. Or they could stop housing roaming animals, Mason said.

"As their animals die and need replacing, zoos should just try replacing them with smaller-ranging species because they’re more likely to be successful," Mason said.

In the past decade, British zoos have gradually stopped replacing polar bears when they die because zookeepers found breeding difficult and noticed erratic behavior in the captive animals, she said.

Zookeepers have long known that caging wandering animals can disrupt their natural habits. But in the past, zoos mainly focused on improving animals’ hunting skills in captivity.

The study, published in today’s issue of the journal Nature, was partly funded by the Universities Federation for Animal Welfare and six British zoos, including those in Bristol and Edinburgh.

Zoos, particularly those in North America, have taken steps in the last few years to build larger, more natural habitats, said Michael Hutchins, director of conservation for the American Zoo and Aquarium Association. Zoos also give animals more variety in their enclosures, such as borders for them to patrol and structures for them to climb, he said.

Mason and a colleague studied 35 captive carnivore species and more than 500 zoos worldwide, drawing on more than 1,000 scientific articles to compile data on infant mortality and on which animals paced back and forth. Pacing is usually a sign that zoo animals lack stimulation.

Polar bears, which naturally range across about 31,000 square miles, or an area the size of South Carolina, fared the worst. They showed an average infant death rate of 65 percent and spent 25 percent of their time pacing in a typical zoo habitat one-millionth of their normal range.

Animals that stick closer to home in the wild, such as the grizzly bear, Arctic fox and American mink, showed lower infant mortality and pacing rates in captivity.