The smaller of the giant panda twins born in Washington, D.C.'s National Zoo over the weekend has died, the zoo announced Wednesday, illustrating the challenges of keeping panda twins alive.
"This is a hard loss for us," zoo director Dennis Kelly said at a press conference. "It's hard to keep these tiny creatures thriving."
Captive panda twins are difficult to keep alive because the mother usually is overwhelmed by caring for two. So zoos have developed a strategy of rotating the twins between mom and an incubator every few hours.
When it works, each baby gets enough time with its mother to be fed by her. If necessary, the zoo supplements her milk with a mixture of infant formula, puppy food, and water.
The demise of the smaller, weaker twin mimics what would happen in the wild.
"A fundamental rule of nature is survival of the fittest," said Marc Brody, founder and president of Panda Mountain, a nonprofit group that works to conserve and restore panda habitat in China's Wolong Nature Reserve.
"When a mother panda has twins in the wild, the mother will only care for the stronger cub, sacrificing the weaker baby to help ensure the more vigorous cub survives," said Brody, also a National Geographic grantee.
The swapping procedure has worked many times in China, zoo officials said. And a pair of panda twins born at the Atlanta Zoo in 2013 is thriving, too. (See “Is Breeding Pandas in Captivity Worth It?”)
But the tactic also "causes a strain on the cubs," Brody says, "and sadly one cub was not strong enough to survive."
Over the past day, the smaller cub had lost weight, was exhibiting possibly respiratory issues, and appeared weak overall. Its condition declined further on Wednesday afternoon, and "despite extreme efforts on the part of our dedicated staff, we weren't able to change things," chief vet Don Neiffer said during the press conference.
Neiffer added that Mei did not show a preference for the larger cub—he says she was resistant about swapping the twins in general.
A necropsy will determine the exact cause of death, Neiffer said.
Meanwhile, Mei Xiang's remaining cub is "doing great," said Neiffer—"very robust and very strong."
Though giant pandas may doing well in captivity, it's a bleaker picture in the wild. Possibly as few as 1,600 giant pandas still roam the mountainous forests of central China, largely due to the fragmentation of their habitat by human development. (See more panda pictures.)
"All of this reminds us that without restoring lost habitat and reconnected fragmented habitat with wildlife corridors, the future for wild pandas will be most challenging," Brody says.