The only female giant panda in the UK will not give birth to a cub this year.

Experts say Tian Tian "resorbed her pregnancy in late term", which is common in giant pandas.

She was artificially inseminated at Edinburgh Zoo for the third time earlier this year.

While male panda Yang Guang failed to successfully mate with Tian Tian, the zookeepers opted for artificial insemination after the failure of a more natural process.

But in a statement this morning, the zoo said: "Based upon our scientific data, the window has now passed during which Tian Tian would have given birth".

The CEO of the Royal Zoological Society of Scotland, Chris West, said: "Tian Tian is still showing behaviour of a pregnant panda, being sleepy and off her food, but we now must assume she has resorbed her pregnancy in late term".

"This year we believe we have achieved the world's most comprehensive hormone analysis of an individual female giant panda".

The zoo adds that it will conduct "an exhaustive review and consult with other colleagues".

Yesterday, Tian Tian marked her 12th birthday.

Giant pandas - an endangered species - have unusual reproductive habits, which has caused many challenges in terms of conservation.

The difficulties include short fertility windows and very fussy mating habits. Zoologists have also been unable to conclusively identify the gestation period.

This is as a result of a process known as 'delayed implantation', where the fertilised egg remains in the reproductive tract for a certain period of time before implanting in the womb and beginning the process of full growth.

The period between mating and birth has ranged from 95 days to 160, and it has been suggested that this can result in the cub being born in more favourable birthing conditions.