Look at this face.Heinz-Peter Bader / Reuters

The nation’s capital received its favorite kind of news this week: panda news.

The National Zoo announced Wednesday night that giant panda Mei Xiang, mom to two-year-old and national treasure Bao Bao, may be pregnant, and could give birth as early as next week or early September. The zoo released a sonogram showing what veterinarians believe to be a developing fetus, and its director said everyone there remains “cautiously optimistic.”

The zoo is being cautious for a reason. Breeding captive pandas—and later caring for their offspring—is a difficult and fragile process. In the United States, only two captive pandas have successfully bred naturally: Gao Gao and Bai Yun at the San Diego Zoo. As recently as the 1990s, io9’s Jason G. Goldman wrote last year, only 30 percent of captive giant pandas successfully reproduced, and more than 60 percent of those cubs died in infancy.

Here’s what scientists discovered in their early efforts to naturally breed members of the endangered species, according to Panda International, a nonprofit conservation group:

[Pandas] either lost interest in mating the natural way or simply did not know how… timing is everything—and it is working against them. A female panda has a single estrous cycle once a year, in the spring… and she’s only actually fertile for 24 to 36 hours.

That’s a very small window. Paul Bisceglio described Mei Xiang’s particular breeding experience—a few months before she gave birth to Bao Bao—with Tian Tian, the zoo’s male giant panda, in Smithsonian magazine in 2013:

The two had become rambunctious leading up to the encounter, and spent days staring longingly at one another through the fence that divides their yards… Despite the flirtatious fireworks, though—and while it was the seventh year in a row the two had been put together to mate—the two pandas again failed to copulate. As she has in the past, Mei Xiang flopped on her belly like a pancake when she met with Tian Tian—the opposite of good mating posture, which would have her rigid on all fours—and Tian Tian went about his usual routine of stomping around and standing on her, clueless what to do.

When natural breeding fails, scientists turn to artificial insemination, which has become common in panda breeding facilities around the world. The latest technology allows scientists to track female pandas’ hormones and determine the optimal time to artificially inseminate them with freshly collected or frozen samples from male pandas. In April, Mei Xiang was artificially inseminated with semen collected from a giant panda named Hui Hui, who lives in a conservation center in Wolong, China, and another sample from Tian Tian. Her two cubs, Bao Bao and 10-year-old Tai Shan, who lives in China, are both products of artificial insemination.

Detecting pregnancy in pandas isn’t easy, either. The tiny fetuses are difficult to spot during ultrasound procedures. Pandas can experience something called embryonic diapause, in which an embryo becomes fertilized but takes some time to implant in the uterine wall and begin to develop. This can prolong the usual gestation period of 50 days to more than 160 days, according to Panda International. Pandas can also experience “pseudopregnancy,” in which female pandas exhibit the standard signs of being pregnant—they build nests, sleep more, eat less—but are not actually pregnant. When pandas become pregnant, they risk resorbing or miscarrying the fetus—“a substantial possibility” for Mei Xiang, the National Zoo said on Wednesday.

Humans also intervene in the care of newborn panda cubs, which are born blind, hairless and 1/900th the size of its mother—in other words, helpless. Pandas often give birth to twins, but lack the energy to care for two cubs. In the wild, that means one cub is left to die. Not so at breeding centers, where researchers help the mother take care of both. And some caretakers can get pretty creative, as the BBC reported about one Chinese facility in 2010:

Whenever a cub was abandoned after birth, keepers at the Chengdu centre swiftly moved it to an incubator. Panda mothers were tricked into caring for twins as staff stealthily rotated them between their mother and the incubators. The survival rate of cubs rose to 98 percent through this combination of maternal care and artificial support.


At the National Zoo, Mei Xiang will be receiving round-the-clock attention from zookeepers, veterinarians, and scientists for the next few weeks, as Baby Panda Watch 2015 kicks into high gear. And she’ll be getting lots of attention from outside of her enclosure, too, thanks to the zoo’s infamous panda cam.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.