The UK’s only female giant panda had been expected to give birth at the weekend.
But tests have now revealed she may no longer be carrying a cub – the second year running that the zoo’s hopes for a baby panda have been dashed.
In a statement Iain Valentine, director of giant pandas for the Royal Zoological Society of Scotland (RZSS), admitted it could be “bad news” but stressed Tian Tian may yet still give birth.
He said: “As you are all probably aware, giant panda Tian Tian is now past her due date and the evidence suggests that this may be bad news.
“She is still displaying some of the behaviours of a pregnant panda, but the scientific data from the urine analysis of her hormones is becoming more atypical.
“There is still a chance she will give birth to a live cub as her progesterone levels have not yet returned to base.”
Following what appeared to be a phantom pregnancy last year, Mr Valentine said that scientific data suggested Tian Tian had really been pregnant – fake pregnancies are quite common in pandas.
“I must stress – as there has been a lot in the news recently about pandas faking it – that this was definitely not a pseudo or phantom pregnancy,” he said.
A team of panda experts have flown in from China to oversee the pregnancy and Mr Valentine said all were in agreement on Tian Tian’s pregnancy.
Mr Valentine added:
“Although it is still very new, the scientific data does suggest the last point she should have gone into labour was over the weekend. Unfortunately, this did not happen.”
Zoo experts will continue to monitor Tian Tian closely over the coming days and hope to know more towards the end of the week as her cycle comes to an end. The zoo said the panda enclosure will remain closed during this time.
Last week, Dr Frank Goeritz, a German scientist who artificially inseminated Tian Tian, reportedly said the latest hormone test indicated the birth would occur over the weekend.
While Tian Tian’s keepers pointed out they were unable to verify the exact date she would be giving birth, a spokesman for the zoo said they had their “fingers crossed” the cub would arrive.
A number of special measures were also taken to maximise her chances of undergoing a successful labour – a no-fly zone was reportedly observed around the zoo to avoid disturbing the animal, while Tian Tian was also removed from public viewing earlier this month.
A Notice To Airmen was published by the Civil Aviation Authority, asking pilots not to fly in the area if possible and to reduce noise from low-flying planes and helicopters.
Pandas typically give birth to twins in the wild. Yet because they are only able to raise one at a time, the mother often leaves one to perish. If a second cub is born, it will be hand-reared by keepers at the zoo.
Ten-year-old Tian Tian has successfully had twins already, in 2009.
Tian Tian, which means Sweetie, and male Yang Guang (Sunshine) arrived on loan from China in December 2011. They were the first giant pandas to live in the UK for 17 years.
The last pandas in the UK, Ming Ming and Bao Bao, left a zoo in London in 1994 after failing to mate.
The hoped-for birth of Edinburgh’s panda cub came after two previous attempts by the zoo to get Tian Tian to conceive.
Animal protection charity OneKind last night called on RZSS to give up trying produce a cub via artificial insemination.
OneKind’s policy director Libby Anderson said: “We are sorry to hear this pregnancy has not worked out. But we think now is the time to leave these animals in peace.”