Q&A: Edinburgh's giant pandas
Since they took up residence in Edinburgh Zoo, they have become two of the city's best-known characters.
Yang Guang and Tian Tian, the giant pandas, arrived in a 10-year loan deal from the Ya'an reserve in Chengdu, China, on 4 December 2011. The pair, who are are both aged 10, have since attracted visitors from around the world.
Tian Tian conceived for the first time in 2013, but the pregnancy failed. Now the zoo says it believes she is pregnant again and may give birth at the end of the month.
When did Tian Tian become pregnant?
Tian Tian was artificially inseminated on 13 April after she failed to mate naturally.
Experts began to analyse hormone and protein levels on a daily basis in Tian Tian's urine. In July, Edinburgh Zoo announced she had conceived although was not technically pregnant.
On 12 August, Iain Valentine, director of Giant Pandas for the Royal Zoological Society of Scotland, said the latest scientific data did suggest Tian Tian was pregnant and may give birth at the end of the month. Two Chinese experts with experience of dealing with panda births are due to arrive in Scotland later this month to support the Edinburgh Zoo team monitoring Tian Tian.
But Mr Valentine cautioned that the late loss of a cub remains a possibility.
Has Tian Tian been pregnant before?
Tian Tian has given birth to cubs before and Yang Guang has also fathered cubs. But this took place in China before their arrival at Edinburgh Zoo.
They were unsuccessful during 2012's mating season and the following April Tian Tian was artificially inseminated. The zoo says it had been able to confirm she became pregnant in 2013 although believes it she reabsorbed the foetus late term. This is a common occurrence in giant pandas in both zoos and the wild.
How long does a panda pregnancy last?
Pandas normally mate in April or May and the female gives birth in August or September. Both Yang Guang and Tian Tian were August cubs.
Unusually, though, pandas sometimes have what's called delayed implantation which means the length of time from mating to giving birth can be extended because the female panda's body may respond to adverse conditions.
Could there be twins?
Pandas quite often have twins, although, in the wild, the mother would decide quite early which cub was stronger and the other wouldn't survive.
In captivity, every effort is made to rear both cubs. And Tian Tian has had twins in the past.
Would the panda cub or cubs remain in Edinburgh?
Edinburgh Zoo has a financial arrangement with the Chinese authorities.
The zoo will keep Yang Guang and Tian Tian for 10 years at an annual fee of £600,000.
As part of the deal, any cubs will remain in Edinburgh for two years before being sent back to China. At that age, cubs would be independent of their mothers in the wild.
When will the public be able to see any new panda cub or cubs?
It could be several months before Tian Tian and a new panda cub or cubs will be seen by the public after a birth.
Visitors to Edinburgh Zoo need to obtain a free timed ticket to see the panda enclosure. Because of the possible pregnancy, viewing of the indoor dens of the enclosure were closed to the public at the start of August this year. The zoo said this was because it was a "critical time" in Tian Tian's potential pregnancy and she was showing sensitivity to noise.
The outdoor viewing areas remained open but zoo officials say the entire panda enclosure will be closed to visitors from 16 August until further notice. It says visitors with pre-booked tickets for dates after 15 August will be contacted by email with details on how to re-arrange their bookings.
Edinburgh Zoo has indicated the enclosure could reopen several weeks after a birth, with only Yang Guang on view in the first instance.
Why do giant pandas seem to find it so difficult to breed?
The number of giant pandas is very small, perhaps 1,600 in the wild and another 300 in zoos.
One important reason for their decline has been destruction of the bamboo forests where they live in south-west China.
The Chinese recognise that pandas need to be able to move around freely and so are trying to link up existing areas which are presently broken up by roads or railways.
It is also true that female pandas will only mate during a 36-hour window each year.
In the wild, they might have several partners in that period. In captivity, zoos are using artificial insemination to replicate those breeding opportunities.
Some ecologists have argued that pandas are already doomed to extinction because their limited diet makes it impossible for them to adapt.
Optimists say they've already survived for eight million years - considerably longer than humans.
Why did Yang Guang and Tian Tian come to Edinburgh?
There was considerable diplomatic effort on the part of the Scottish and UK governments, with the zoo also making its own case.
Edinburgh Zoo argued that they had suitable staff and could call on outside experts who would work together on panda breeding and conservation.
Since the agreement was reached, staff from Edinburgh have been working closely with Chinese panda specialists.
Scottish keepers have been to the panda breeding centre near Chengdu in Sichuan Province and panda conservationists from China have come to Edinburgh.
Aside from conservation, the giant pandas represent a potential financial lifeline for Edinburgh Zoo which had been suffering falling visitor numbers before Tian Tian and Yang Guang arrived.
In the first year of the Edinburgh pandas, the zoo enjoyed a 50% increase in its visitor numbers, more than enough to cover the cost of payments to China. A report last year from Scottish Enterprise estimated they will generate almost £28m for the Edinburgh economy during their 10-year stay, with an additional £19m being spent in the wider Scottish economy.