Yang Guang, a male giant panda chews on bamboo inside his enclosure at Edinburgh zoo in Scotland April 4, 2012. Staff at the zoo are hoping for a successful mating between Yang Guang and the female giant panda Tian Tian, as female pandas ovulate just once a year with a narrow window of 36 hours in which they can mate. REUTERS/David Moir (BRITAIN - Tags: ANIMALS SOCIETY)