| Edinburgh zoo pandas 'ready to mate'|
|Edinburgh zoo's two pandas are close to beginning their second tryst, after the zoo announced that their short-lived breeding season could start within hours.|
The zoo said that the "love tunnel" separating the neighbouring enclosures for the female giant panda, Tian Tian, and the male, Yang Guang, could be opened on Tuesday afternoon or during the night, to exploit their extremely tight 36-hour breeding season.
The pair's keepers and panda experts from Germany and China believe Tian Tian will be at her most fertile early on Wednesday morning, when the pair would again be put in each other's enclosures being released to meet directly.
Even if the zoo's efforts to coax the pair into a voluntary coupling succeed, biologists under the direction of a Chinese panda expert will try artificial insemination over Tuesday night or Wednesday to increase the chances of producing young.
As well as having a remarkably short breeding season, which accounts in large part for their very low population numbers – it is believed there are only about 1,500 left in the wild in addition to the 350 in captivity – there is also a risk that consummation will fail to produce young.
Tian Tian and Yang Guang – their names translate as Sweetie and Sunshine – have been under close scrutiny and supervision as their breeding season approaches. Tian Tian's sexual hormone levels have been measured daily to predict when they might peak.
In a gesture of politeness, and to allow zoo staff to work without the world's prying eyes, the "panda cam" which beamed live images of their enclosures over the web was switched off several days ago.
Iain Valentine, the zoo's director of giant pandas, said: "The annual panda breeding season is imminent and the next 24 hours are critical. Tian Tian is not quite ready yet, however, her hormones could peak as soon as this afternoon, this evening, overnight or early tomorrow morning – we are now that close. Yang Guang is more than ready and is a completely different animal to this time last year."
Valentine said the pair had been "communicating heavily" through a grate in a short tunnel which divides their enclosures inside a linking building; when they are sufficiently familiar with each other again, that gate will be opened.
"Last year we saw all the right signals at this stage – Tian Tian was calling out repeatedly to Yang Guang and both were heavily interested in each other," Valentine said. "When the door opens the pair will probably wrestle once more to assess each other's strength, which is vitally important for animals of this size and power, and then things should progress from there."
Valentine said Edinburgh's efforts were being supported by Prof Wang of the China Conservation and Research Centre for Giant Pandas in Wolong and specialists from the Leibniz Institute for Zoo and Wildlife Research in Berlin.
"Artificial insemination will follow on from the natural mating attempts, whether they mate naturally or not. We have several world-leading experts on artificial insemination and reproduction management of endangered species on hand to assist RZSS [Royal Zoological Society of Scotland] specialists," he added.
"Two teams will work simultaneously with Tian Tian and Yang Guang in their indoor viewing areas, firstly to get a fresh semen sample from the male and then to artificially inseminate the female.
"The timing of procedure is critical. As soon as Tian Tian hits peak her hormones will start to fall and artificial insemination will probably take place very soon afterwards; this again could be as soon as this evening, overnight or tomorrow morning."
The pair were loaned to the zoo for 10 years in a deal including a $1m (£653,000) per year fee to the Chinese, as a diplomatic gesture to cement the increasingly close economic ties between China, now the world's second largest economy, and Scotland.
The pandas flew into Edinburgh in December 2011, several months after the loan deal was formally agreed in tandem with multimillion-pound investment agreements by Chinese companies in the Grangemouth oil refinery near the Scottish capital.
Last year's first pairing failed, after the pandas' increasingly amorous advances ended without any intercourse.
A successful breeding of panda cubs would be immensely rewarding for the zoo; as the zoo's senior staff were in the latter stages of negotiating the loan, it emerged that in 2010 its owners, the Royal Zoological Society of Scotland, needed a £2m rescue loan after suffering a £1.5m loss and a sharp fall in visitor numbers.
Even one panda cub would be expected to draw large crowds, boosting the zoo's gate receipts and merchandising sales, and helping meet the significant costs of keeping the panda family.
In addition to the £653,000-a-year loan payments, the zoo has to specially import bamboo by air from Amsterdam, while spending more on staff costs, equipping and maintaining the pandas' £250,000 enclosures, and on a major panda-related marketing campaign.