Video: Sumatran tiger cubs make first public at Smithsonian's National Zoo in Washington

Two cubs from highly endangered species had to pass swimming test before they could be allowed out in main enclosure.

Large or small, cats are graceful, specialized, and powerful animals. Yet, they are among the most endangered. Zoo conservation biologists are working with colleagues on lions' home ground in Africa, and tigers' in Asia, to develop the scientific understanding necessary for effective conservation. Zoo scientists are studying the ecology, behavior, and reproductive biology of tigers, lions, and many other cat species, including cheetahs, clouded leopards, and fishing cats.

Learn more or book plan your trip at  http://nationalzoo.si.edu/animals/greatcats/