Teaching an endangered zoo animal to love again
6 July 2014 Last updated at 04:29 BST
A quarter of the world's mammals and 41% of amphibians are now threatened with extinction, according to the International Union for the Conservation of Nature.
The organisation has assessed some 71,000 different species of animals, but says that figure needs to be more than doubled to get a real picture of the global threat to wildlife.
But how do you go about counting wild animals? And what happens when animals are struggling to breed?
Well, every year, a group of international students converge on the Smithsonian's Conservation Biology Institute in a remote part of Virginia to find out more.
The BBC's Jane O'Brien went out to join them.
Produced by David Botti