Mei Xiang at the National Zoo in January.
"Mei Xiang is our female giant panda and she is on the monitor on the right and we are looking at what we hope is a pregnant giant panda," says Brandie Smith, a senior curator at the panda exhibit at the National Zoo.
Mei Xiang was inseminated at the end of January, and now zookeepers are waiting to see if she's pregnant. Sometimes it's hard to tell.
"That’s the complicated thing," says Smith. "Pandas are either pregnant or they go through something called a pseudopregnancy. And in a pseudopregnancy almost everything is the exact same as if she were having a baby. Her hormones are the same; we track her hormones every day. Her uterus develops, and the wall thickens as if she were pregnant. She gets very lethargic – she does all of these things whether she’s pregnant or not."
It's not clear why this happens, but panda embryos can take a while to implant in the uterus. So the panda's internal system may just be playing it safe – just in case there’s an embryo floating in there that hasn’t settled yet. Regardless of the reason – pregnancy or fake-pregnancy – behavioral changes will be apparent.
"Comparing pandas to humans, at least the ones I know, she's not crabby when she's pregnant, but she’s spacey,” says Smith. "A look in her eyes that says she’s not quite engaged with us and the world around her."
Smith says Mei Xiang is getting pickier with her food too.
“There's very little that can get her to move so we can train her, so now we have a panda who will only work for pears."
Smith also says that Mei Xiang appears to be getting nursery ready.
"She builds a nest, which she does out of bamboo. She shreds bamboo in her den. There's another thing she does which is absolutely adorable, she cradles her toys. She actually cradles them, she tends to them and cradles them, and she's doing that now and it’s an amazing behavior."
Zookeepers have to keep close track of this because pandas don’t have due dates.
"You can't just count down 9 months, plus or minus two weeks," Smith says. "With pandas it can be as brief as 2-3 months or 9 months is the record."
Zookeepers do an ultra sound on Mei Xiang every day. An ultra sound on a panda is very similar to an ultra sound on a human, says Smith.
"We have the same equipment we put gel on her belly - I guess the difference is we shave the belly of a panda and we don't shave the belly of a human. We’re hoping that we can see a fetus."
No luck yet – panda fetuses are the size of a peanut, and when they're born they are about the size of a stick of butter.
There is one telltale behavioral sign that might tell zookeepers whether Mei Xiang really will be a mom again.
"Behaviors change a little as she approaches birth. She becomes very restless. She would start pawing at things. And once we see those behaviors starting we’ll come in and be prepared for a birth."
Volunteers are watching around the clock, looking for the ultimate sign that Mei Xiang is really pregnant.
"Well we will know when she has a cub," says Smith. "If she’s pregnant or not -- we'll hear the squealing on the monitors."
Zookeepers estimate she could give birth between now and possibly the middle of July.