Scotland's giant pandas could be ready to mate within the next month, according to zoo experts.
Both the female Tian Tian (Sweetie) and the male Yang Guang (Sunshine) have already started to show important changes in their behaviour, indicating their readiness to mate soon, panda specialists at Edinburgh Zoo said.
Yang Guang recently began doing handstands against trees, walls and rocks, scent-marking as high up as possible - known as a display of virility in the wild.
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Meanwhile Tian Tian has already started calling out to the male - which is common during breeding season.
Experts 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.
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 pandas were first introduced to each other last April, however they did not end up fully mating. Female pandas are in season for less than 48 hours.
Iain Valentine, director of giant pandas and strategic innovations for the Royal Zoological Society of Scotland, said: "We're delighted that both Tian Tian and Yang Guang have started to scent mark and call, both clear behavioural indicators of courtship and mating behaviour.
"Although both giant pandas are showing these changes in their behaviour, it is still early days yet and way too early to give any accurate prediction on timings, however, early indicators do suggest the breeding season will probably fall in March this year.
"In reality we could be as little as four weeks away, although equally the big day could still be as far off as eight weeks.
"This year we will combine both natural and assisted reproduction methods. This follows the best practice methodology adopted by other panda-keeping zoos around the world and gives our giant pandas the best possible chance of success."