Banham Zoo Siberian tiger births
A pair of Siberian tiger cubs have been born at a zoo in Norfolk.
Zoo keepers at Banham watched on CCTV as the endangered cats, also known as Amur tigers, entered the world on Friday.
Mike Woolham, animal manager at Banham Zoo, said there were fewer than 400 of the tigers left in the wild, which is "critically low".
The cubs' father Kuzma is ranked as one of the most important males in the international breeding programme.
It was thought important to breed Kuzma, born at the zoo in 2008, as his genes are rare in the captive population.
Mr Woolham said: "There are now thought to be more in-captivity in-breeding programmes than there are in the wild, which is a real tragedy."
The cubs are the first successful litter bred from the male and his mate Sveta, which arrived from Lisbon Zoo in Portugal two years ago.
Kuzma is the son of a tigress who drowned in a natural pool at the zoo in 2010 while pregnant.
Mr Woolham said the death was "dreadful" but the cubs' birth now "puts a lid on it".
Tigers are pregnant for around 100 days but Banham staff had to wait an extra six days for Sveta's cubs to arrive.
The mother and her babies, born with fur and striped markings, are being monitored via tiger-proof cameras as keepers do not enter the enclosures.
The cubs will be left to come out into the open enclosure of their own accord but probably will not be spotted for the next six weeks.
"We've got the CCTV cameras so we can see absolutely everything that is going on," said Mr Woolham.
"We have a monitor screen up outside the enclosure so Sveta and the cubs keep their complete privacy but the keepers and people coming to the zoo can see what's going on inside the cubbing box."
It will be six weeks before staff can get close enough to the cubs to tell their sex and name them.
The animals will be taken to another zoo when they reach 18 months to be paired with a mate as part of the Siberian tigers' international and European conservation programme.
Most of the wild population is found in the Russian Far East, roaming around the Amur River.
The tigers are under threat from hunters and the loss of natural habitat.