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.he 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.