Public viewing was halted last week in the hope that male Ri Ri – who zookeepers confirmed has looked friskier in recent days – will take advantage of the fleeting window that female Shin Shin is in heat.
“There’s really only a couple of days a year when a panda can get pregnant,” a spokesman from Ueno Zoo’s education department said.
“Pandas are solitary animals and the only time you will see them together is the mating season.
“Usually they just sit apart from each other chewing their food, but Ri Ri has been looking more amorous of late.”
The cuddly creatures, both 10 years old, have a choice of two rooms in which to snuggle up to one another, although officials insist they will not interfere with the courting process.
“There is a spare recreational room for them out the back,” said the spokesman. “But we won’t be giving them any special food or dimming the lights for them.
“Nobody knows what kind of mood to create for animals to feel romantic,” he added. “They don’t just get into the mood with soft lighting like humans.”
Shin Shin, who was brought from China five years ago, just before the devastating tsunami in Japan’s north-east, gave birth to a baby in 2012 but the cub died from pneumonia six days later. She had a phantom pregnancy in 2013 and the pandas have not bred since.
Giant pandas are notoriously clumsy at mating, with males said to be bad at determining when a female is in the right frame of mind and often befuddled at knowing what to do next.
In the event the animals do feel compatible, sex is frequently over too quickly to impregnate the female, who is only receptive to the proposition for two or three days a year between February and May.
“It’s true the females are picky,” the zoo spokesman said. “In their natural habitat, they get to select the male.”
According to estimates, less than 2,000 giant pandas remain in the wild, in three provinces in south-central China.
Should Shin Shin rebuff Ri Ri’s advances for a third straight year, Ueno Zoo will consider artificial insemination, the official confirmed.
“It remains an option but we’ll see how they get on first,” he said.