Why Is It So Hard to Breed Giant Pandas?

Over the weekend, giant panda Mei Xiang gave birth to twin cubs at the Smithsonian National Zoo, to the delight of conservationists and keepers (and everyone who loves roly-poly fur balls). Just three days earlier, veterinarians weren't even sure if Mei Xiang was pregnant, though they spied what they believed was a developing fetus on an ultrasound.

Now, the two tiny cubs are being swapped every three hours between their mother's care and an incubator, in an attempt to keep the fragile babies alive. It's an exhausting process to get to this point, one that takes months (sometimes years) of careful monitoring and planning. We often hear about how difficult it is to successfully breed giant pandas in captivity, but why is it so damn hard to make some babby pandas?

1. Pandas only ovulate once a year.

The window for knocking up a lady panda is pretty narrow, said Pierre Comizzoli, a veterinarian and reproductive physiologist with the National Zoo. Female giant pandas are able to conceive only once a year, within a period of 36 to 40 hours.

2. Male pandas can be kind of shitty in bed.

Comizzoli told me they always try to encourage natural breeding when a female is ovulating, but sometimes the male pandas don't get the job done.

"Our male has never really been able to breed with the female properly," Comizzoli said. "We always offer the male a chance to breed with the female, but at some point we have to make a decision to artificially inseminate because we don't want to miss the opportunity."

3. There's no such thing as a panda pregnancy test.

After artificial insemination, predicting whether or not a female panda is pregnant is about as accurate as a horoscope, Comizzoli told me. The progesterone levels in a female panda are the same whether she is pregnant or not, he explained, leading to what's dubbed a pseudo-pregnancy. The female will exhibit all of the same signs of a pregnancy (building a nest, sleeping longer, eating a bit less) but with no fetus in her womb.

"We don't really know what hormone is the indicator of pregnancy," he said. "But we know for sure that when this production of progesterone starts to decrease, then we are approaching either the end of her pregnancy or the end of the pseudo-pregnancy."

4. Panda fetuses can be confused with poop on an ultrasound.

Panda fetuses don't develop a whole lot in the uterus. They're very tiny in proportion to their mothers, Comizzoli said. Those mothers are also built in a way that complicates things further, he explained.

"They have really large abdomens that have a lot of bowels filled with bamboo fiber and stuff like that," he said. "It's really difficult to detect the presence of the uterus and to see in the uterus the presence of a fetus."

That's why when vets kinda, sorta thought they saw a fetus in last week's ultrasound, they were pretty psyched.

5. The length of a giant panda's pregnancy can vary.

Unlike some other mammals (including humans), which have a fairly standard gestation period, a female panda can be pregnant for anywhere from less than three months to a little over six months, Comizzoli said. This is because the giant panda tends to give birth when environmental conditions are optimized, to ensure the survival of the cubs, he explained.

6. Panda cubs are born completely helpless.

Human babies are notoriously ill-equipped for survival when they're born, compared to some other mammals like cows and deer that give birth to babies who can already freaking walk. But giant panda cubs make even human babies look pretty far advanced. The tiny, blind, hairless little guys are completely helpless, especially for the first two weeks of their life, Comizzoli told me. That's why the keepers are currently pulling duty with Mei Xiang to feed and coddle the cubs.

"We are still in a really critical period of time because the cubs are extremely vulnerable and fragile," Comizzoli said. "Three years ago we lost a cub at the age of six days because there was a malformation. But so far the mother is dealing pretty well with the cubs one at a time."

After clearing all those hurdles to get to this point, the panda keepers and vets are working around the clock to try to ensure these cubs grow up healthy, like Mei Xiang's older offspring Bao Bao, who celebrated her second birthday on Sunday: