The UK's only male giant panda has started showing signs of readiness to mate.
Yang Guang (Sunshine) recently began doing handstands against trees, walls and rocks, and scent-marking as high up as possible - known as displays of virility in the wild.
Experts at Edinburgh Zoo are now hoping Yang Guang and the female Tian Tian (Sweetie) could be ready to mate within the next month.
At the zoo, Yang Guang could be seen looking through a closed gate linking his enclosure with Tian Tian's.
He was also reclining on his rock eating bamboo, increasing his daily intake from 80lb per day to 110lb. This will go up to 220lb as breeding gets closer. His goal is to drive his weight up, as in the wild he would need enough energy to travel to female territories and compete against other males.
Meanwhile, Tian Tian has started calling out to him, which is common during the breeding season.
Female pandas ovulate once a year, giving a narrow window of less than 48 hours in which they can get pregnant.
Keepers are able to predict when both giant pandas are ready to breed by a combination of behavioural observation and hormone testing, but to date no hormonal changes have been seen in either panda. The pandas were introduced to each other last April but they did not end up fully mating.
Edinburgh Zoo, where the pandas have lived since their arrival from China in December 2011, has employed a number of measures to synchronise the breeding cycles of the pandas, including controlled lighting, urine testing for hormone levels and enclosure swapping.
The pair are the first giant pandas to live in the UK for 17 years.