According to a study from Oxford University biologists Georgia Mason and Ros Clubb, the most serious problems seen in zoos, like high infant mortality rates and psychosis, stem from having not enough space. Animals who wouldn't naturally travel far in the wild tend to fare better than those who do.
But as it turns out, polar bears have one of the largest home ranges of any land mammal on the planet -- reaching upwards of 31,000 square miles. Researchers found that the typical polar bear zoo enclosure equates to one millionth of that size.
This would explain, they say, why confined polar bears often exhibit odd behaviors, like bobbing or pacing restlessly back and forth, and why 65 percent of their cubs born in captivity die within a month.
So having room to wander, as nature intended, isn't just a luxury for polar bears; it's likely an essential part of their biology.
"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," says Mason. "They might be designed in such a way that roaming makes their central nervous system develop properly."
To prevent the further suffering of polar bears in captivity, the researchers arrive to a simple conclusion:
"Our findings indicate that the keeping of naturally wide-ranging carnivores should be either fundamentally improved or phased out."