Children Watch Hybrid Bears at National Zoological Park, by National Zoological Park (U.S.), 1950's, Smithsonian Archives - History Div, Children watch hybrid bears through iron bars at the National Zoo during the 1950's. Older enclosures such as these were commonly used to display zoo animals. Although these types of enclosures are not the most visually appealing, they were practical for keeping a clean environment essential for the health of the animals. Today, as zoos modernize, enclosures that exhibit several species in a more naturalistic setting are more popular..