The death of an 8-day-old panda at the National Zoo is a good reminder that "nature is in charge," says Pierre Comizzoli, a research biologist at the National Zoo who was part of the team looking into the death of the zoo's baby panda on Sunday. "It might have happened in the wild, too."
About 75% of pandas born in the United States survive their first year, a figure similar to the rate of other animals, Comizzoli says. The overall survival rate for cubs born in Chinese breeding centers, where most captive breeding is done, is between 35% and 48%, according to the Chengdu Research Base for Giant Panda Breeding.
MORE: Panda cub seen on camera at National Zoo
In Washington, D.C., the zoo's female giant panda Mei Xiang, 14, gave birth on Sept. 16. Veterinarians had been monitoring mother and her three-and-a-half-ounce cub via camera. The cub was found dead Sunday morning after keepers heard sounds of distress from Mei Xiang. A necropsy showed the cub had liver problems and fluid in its abdomen, but it's too early to say if that contributed to the death, according to the zoo's chief veterinarian, Suzan Murray. Final tests results won't be available for two weeks.
It's a small window of opportunity and if you miss it, you have to wait another year --Pierre Comizzoli
There are an estimated 1,400 to 1,600 pandas living in the wild in China and an additional 350 or so in captive breeding programs in China and elsewhere.
Pandas are difficult to breed in captivity because the females are fertile for only one 36-hour period per year, generally sometime between March and May.
"It's a small window of opportunity and if you miss it, you have to wait another year," Comizzoli says.
To make sure the zoo doesn't miss it, Mei Xiang's urine is tested to see if she's nearing ovulation. "She's followed on camera, so whenever she pees anywhere, someone immediately goes into the pen and collects the urine," Comizzoli says.
Mei Xiang has a mate, Tian Tian, 15, whose sperm has been used to father two cubs previously. However, he's proven to be "unskilled" at natural breeding, Comizzoli says. "We always give him a chance. We thought year-by-year he might learn, but unfortunately 36 hours isn't enough for training," he says, so the zoo artificially inseminated Mei Xiang with Tian Tian's frozen sperm.
She gave birth once before, in 2005, to a healthy cub named Tai Shan, now living at the China Conservation and Research Center for the Giant Panda in Wolong, China.
Mortality is high in the first two weeks of any animal's life, Comizzoli says. After that, animals "have a good chance of survival. That means that there are no genetic abnormalities and that the baby is OK."
Panda infants are especially fragile because they're born so tiny -- about the size of a stick of butter. An adult female panda can weigh around 200 pounds. In captivity and in the wild, panda mothers are known to crush or smother their babies as they nurse. That didn't happen in Mei Xiang's case.
"They're born very small in comparison with their mothers, and they're born relatively underdeveloped, and they do take a tremendous amount of care on the part of their parents," says San Diego Zoo spokeswoman Christina Simmons. San Diego has had a highly successful breeding program for pandas since 1999. The zoo's sixth cub was born July 29.
Up to 40 staff and wildlife experts were involved in helping Mei Xiang conceive and were monitoring her after the cub's birth. "We were all so happy together, and now we're all sad together. But at the same time we're trying to see what we learned this time," Comizzoli says. The fact that the cub was born from frozen sperm "is a partial success" and will help further breeding efforts, he says.
There has been an outpouring of support for the staff on Facebook and Twitter. The Panda habitat is currently closed to zoo visitors, so it has not become a site of mourning for the public.
Captive breeding of pandas took off in China about 15 years ago, Comizzoli says. Through improved diet, disease elimination and better tests for ovulation and sperm viability, breeding programs flourished. China has two main programs and allows pandas to be housed at zoos around the world that take part in the breeding program, mostly through the exchange of frozen sperm.
China has moved to protect wild panda's natural habitat, establishing several panda reserves and cracking down on poaching and illegal lumber harvests in the iconic animal's mountain homeland. However, pandas are still considered an endangered species by the the International Union for Conservation of Nature.