Pictures of Big Cat Crossing at the Philadelphia Zoo

Amur tigers walk across a passageway after a new conference at the Philadelphia Zoo, Wednesday, May 7, 2014, in Philadelphia. The see-through mesh pathway called Big Cat Crossing is part of a national trend called animal rotation that zoos use to enrich the experience of both creatures and guests. (AP Photo/Matt Slocum)
May 7, 2014 9:22:35 AM PDT