Mating tests begin on Edinburgh's giant pandas Edinburgh Zoo on Monday started daily tests to pinpoint the best time for its pair of giant pandas, given to Scotland by China, to try to produce a cub. Zoo-keepers are collecting urine and vaginal samples from female panda Tian Tian, whose name means Sweetie, to check her oestrogen levels. Female pandas are only interested in mating for three days a year and Tian Tian is expected to be in heat at some point between the start of March and early May. The tests will help work out the best time to start encouraging her to breed with Yang Guang (Sunshine), who arrived in the Scottish capital alongside her to great fanfare in December. "It is vital for us to have as full a picture as possible of when Tian Tian is receptive to mating, as the window will only be three days," said Iain Valentine, director of research and conservation at Edinburgh Zoo. Although not with each other, both pandas have bred before and we are fairly optimistic we can achieve a successful panda breeding. Signs have been positive to date and Tian Tian has had time to get used to the scents and sounds of Yang Guang. The zoo hopes the pair, which have received thousands of visitors in the past three months, will make use of a "tunnel of love" built between their separate enclosures. Pandas' reproductive systems make breeding notoriously difficult and there are fewer than 1,600 of the endangered species left in the world, according to the World Wildlife Fund. Females can only become pregnant during a 12- to 24-hour period during the entire year, and the males' proportionally short penises mean a precise position must be achieved for mating to be successful. Conservationists have tried a range of methods, from artificial insemination to pornography and viagra, in a bid to boost numbers. Tian Tian and Yang Guang are in Edinburgh on a 10-year loan from China, following five years of high-level political and diplomatic negotiations.