Why Giant Panda Twins Don't Always Fare Well

Mei Xiang, the giant panda at the National Museum in Washington DC, gave birth to a lively squeaking cub on Friday last week and a day later she delivered the cub's twin, which was stillborn.

The giant panda reportedly cradled her stillborn cub, grooming it for 17 minutes before letting it fall lifeless to the floor. On Sunday, zookeepers and veterinarians at the National Zoo gave the surviving twin a positive health evaluation.

But why did one cub survive while the other died?

In the case of Mei Xiang, the healthy cub's twin was severely deformed and was never alive in the womb, according to the National Zoo, which also said that stillbirths in giant pandas are quite rare.

"The animal had extensive abnormalities around its head and was missing its brain," the Washington Post said of the stillborn cub.

Twins are common among giant pandas. In the wild and in other zoos around the world a giant panda mother will give birth to twins about 50 percent of the time, according to Rebecca Snyder, the curator of mammals at Zoo Atlanta, who spoke to National Geographic last month.

Panda twins born in the wild will suffer a grim fate. The mother will determine which of the cubs is healthiest and devote her time and energy to it, abandoning the weaker of the twins.

Marc Brody of China's Wolong Nature Reserve, which breeds pandas in captivity, told National Geographic on Saturday that "Immediately a mother panda knows it's a tough world out there and goes for the survival of the fittest."

A giant panda also gestates for between just three and five months, giving birth to some of the most extremely premature babies in the animal kingdom. Newborn giant pandas are about the size of a stick of butter and way merely 1/900th of their mother's weight. Blind and hairless, they are unable to move on their own until about 80 days old.

As such, a newborn panda will need round-the-clock attention from the mother. The cub will feed as many as 14 times a day for up to 30 minutes at a time. It is believed that the mother is unable to produce enough milk to sustain two cubs at once. Also, because the cub is completely dependent on the mother, handling two cubs at once can also be challenging test of dexterity.

"[The mothers] have to hold the cubs and position them for nursing in the first couple of weeks. Sometimes they're just not capable of getting them positioned and one of them fails," Snyder said.

In July, Zoo Atlanta's giant panda Lun Lun gave birth to twins. Panda twins born in captivity stand more of a chance of survival than if they were born in the wild. At a zoo, pandakeepers will never allow the mother to have both of the cubs at once. Zoo staff will keep one cub in an incubator and manually nurse it if necessary.

"If we're not able to swap them out as frequently as we want to, then we'll supplement them with a little bit of formula to make sure they're getting enough to eat," Snyder said.