Panda twins born in US zoo are strong and healthy
Zookeepers in Washington DC are optimistic about the survival chances of twin cubs born to giant panda Mei Xiang.
In more than three decades of trying to breed pandas at the National Zoo, there has been plenty of heartbreak, and more cubs have died than survived.
But now zoo officials do not just have an apparently healthy pair of twins, born on Saturday night, they have a template to follow that gives the cubs a strong chance of survival.
Pandas will not usually nurse twins if left to their own devices, as they will care for one and allow the other to die.
But in the past decade, Chinese breeders have devised a system - every few hours, they swap out the cubs, giving each one the critical time it needs to nurse and bond with its mother. Meanwhile, the other one is kept in an incubator.
Panda keepers at the Smithsonian's National Zoo will continue performing these delicate swaps as long as needed if Mei Xiang lets them.
By late Sunday afternoon, the twins had traded places three times without incident, with Mei Xiang cradling them in turn.
"If she gets aggressive toward us, we're not going to get that close," giant panda biologist Laurie Thompson said.
The swapping technique helped twin pandas born two years ago at Zoo Atlanta to survive. That was the second set of panda twins born in the US. The first, born at the National Zoo in 1987, both died within days.
Scientists in China have learned much more about panda breeding since then. Two decades ago, the survival rate for panda cubs was under 20%, but now it is more than 80%, zoo director Dennis Kelly said.
"We've all been involved in events that don't go so well, so we are ecstatic that things are going great," said Don Neiffer, the zoo's chief vet.
The cubs have squealed loudly when taken away from Mei Xiang - one of several signs that they are strong and healthy.
Although one weighed roughly 4oz and the other was just 3oz at birth, both are considered within the healthy range. They are blind, and pink in colour, with wispy white fur.
The second cub was given a serum drawn previously from Mei Xiang's blood because it had not had a chance to nurse. Keepers are prepared to bottle-feed the cubs if necessary, but they will not do it unless one of the pandas is underweight or has other health problems.
Mei Xiang has given birth to two surviving cubs, including Tai Shan, a male born in 2005, who is now in China.
Her daughter Bao Bao celebrated her second birthday on Sunday and put on a show for hundreds of delirious panda watchers as she devoured her "cake" - a frozen concoction made with honey, apples, carrots and bamboo.
Ling-Ling and Hsing-Hsing, the panda pair lent to the US by China after Richard Nixon's historic visit in 1972, successfully mated five times, but none of the cubs lived longer than a few days.
Mei Xiang gave birth to a cub in 2012 that died after six days.
The new additions mean that for the first time the zoo has five pandas in residence. In addition to Bao Bao, Mei Xiang and the new cubs, the zoo is also home to an adult male panda named Tian Tian. In the past, the zoo has never had more than three pandas at one time.
Tian Tian is the father of Mei Xiang's previous cubs. This time, she was artificially inseminated with semen from Tian Tian and another panda in China that was determined to be a good genetic match.
Zoo officials said it will be three to four weeks before the cubs' genders are known, and they will not be named until they are 100 days old, per Chinese tradition.