Giant Panda Tian Tian is seen at the Giant Panda exhibit at the Smithsonian's National Zoo his mate Mei Xiang rests indoors August 7, 2013 in Washington, DC. Scientists at the National Zoo say Mei Xiang is experiencing hormone changes and showing increasingly obvious behavioral shifts indications that she could be pregnant. Mei Xiang has had only one successful pregnancy since 2005 when she gave birth to Tai Shan. AFP PHOTO/Brendan SMIALOWSKI (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
