LONDON (AFP) - He is performing handstands and eating constantly, and she is spraying her home with alluring scents - all the signs point to mating season for Britain's giant pandas.
Experts at Edinburgh Zoo in Scotland, which acquired the pair from China in December 2011, believe the mating window of just a few days each year will take place in the next three weeks.
Female panda Tian Tian, whose name means Sweetie, failed to mate with Yang Guang (Sunshine) last April, but the zoo has made some changes which it hopes will up their chances this year.
"We're doing everything we can to get a pregnant panda," Iain Valentine, director of giant pandas for the Royal Zoological Society of Scotland, told AFP. "I've got high hopes of this year."
The lights in their separate enclosures have been timed to simulate natural light levels outside, and Tian Tian's hormone levels have been closely monitored since Jan 1. And since last month, the pandas have been given time in each others' enclosures which allows them to pick up scent marks, a crucial part of the courtship.
Yang Guang is filling up on bamboo in anticipation of the big event, building up his muscle reserves and performing handstands to mark trees, walls and rocks with his scent.
The higher the scent, the stronger the panda, and the more likely a potential rival would be deterred. And at nine years old, Yang Guang is in peak physical condition.
"He needs good muscle tone because in the wild, he would be competing and moving across large areas of land, and fighting," Mr Valentine said.
For her part, Tian Tian has been scent marking around her enclosure to let her beau know that she is ready to mate, and the normally quiet pair have been calling out to each other.
"This year, we've been taking the male and putting him into the female enclosure, where he's picking up her chemical cues. And that gets him all pumped up," Mr Valentine said.
The pandas look on course to mate around the same time as last year, at the end of March or the beginning of April. The cameras that monitor their movements for eager fans will be switched off to give them some privacy, but nothing is left to chance.
"We're going for a natural mating, and we'll be repeating the process with artificial insemination," Mr Valentine said.
The zoo will not know until the second half of August if Tian Tian is pregnant, and then they will only have three weeks before a tiny, blind, bald baby panda is born. And that would not necessarily spell success.
Two pandas in a zoo in Tokyo had a baby last year, the first giant panda cub there for 24 years, but it died of pneumonia a week later.
The Tokyo pandas, female Shin Shin and her companion Ri Ri, mated again this week, although Ueno Zoo in Tokyo did not afford their pandas quite the same privacy as Edinburgh did - it posted a 30-second video of the panda hanky panky on its website, www.tokyo-zoo.net.
Pandas, whose natural habitat lies in mountainous southwestern China, have a notoriously low reproductive rate and are under pressure from factors such as habitat loss. China has about 1,600 pandas living in the wild.