But that's starting to change. Though these langurs aren't officially endangered, there are fewer in the wild than people once thought. So zoos are working hard to boost the langur population. Beth Schwenk plays matchmaker to America's langurs. Philadelphia Zoo keeper Beth Schwenk tracks down the family history of every spectacled langur in U.S. zoos.
Zoos use studbooks to make decisions, like when to breed certain animals.
Our goal is to build the population from about 40 to 75 . . . By helping to manage the population of zoo langurs, Beth hopes to build public support for langurs in the wild. In a remote swamp, Carel van Schaik tracks tool-using orangutans. Years ago, an exhausted Carel van Schaik almost gave up on his study of Sumatran orangutans. To get to the orangs, he had to wade through chest-deep water and battle the constant buzz of mosquitoes.