The National Zoo's giant panda Mei Xiang, who was artificially inseminated, has started to show some changes in her behavior that may be a sign that she’s in fact pregnant — or having a false pregnancy. (Skip Brown/Smithsonian's National Zoo/Skip Brown/Smithsonian's National Zoo)

The National Zoo is closing its Panda House starting Wednesday, and possibly for the rest of the month, because giant panda Mei Xiang might be pregnant.

Zoo experts said Mei Xiang, who is 21, started to show changes in her behavior this week that might be a sign she’s pregnant — or having a false pregnancy. Her levels of progesterone are rising, which is usually an indication of possible pregnancy, zoo spokeswoman Devin Murphy said.

On Wednesday, the panda also showed another sign. Officials said she chose to stay inside rather than go into her yard to eat bamboo. “That’s unusual,” Murphy said.

It’s tricky to get a giant panda pregnant.

They are in estrus for only 24 to 72 hours each year. Because the window is so short, zookeepers have to be ready. Plus, pandas often have false pregnancies, triggering elation but then disappointment among panda watchers.

Typically when a female giant panda is pregnant, she will spend more time sleeping and less time eating. Pregnant pandas also become more sensitive to noise, which is why officials decided to close the Panda House.

“We want to make sure she has a nice, quiet environment for now,” Murphy said.

She’s also licking her paws and cradling toys — two more signs she could be pregnant. And officials said she has “also started building a small nest of shredded bamboo in her den” and adds to it at night.

In March, Mei Xiang was artificially inseminated using semen from Tian Tian.

Officials said they won’t know for sure if she’s pregnant until about the end of August. The Panda House will stay closed until she returns to normal behavior or after there’s a panda cub, zoo officials said.

Zookeepers have been doing regular ultrasounds for the past month but “haven’t seen anything yet,” Murphy said. Mei Xiang is on the older side for giving birth, but officials said there are giant pandas that have successfully given birth when they were older than her.

Officials said zoo visitors can still see Bei Bei, who was born in 2015, and Tian Tian outside in their yards and watch Mei Xiang on the panda cam. Mei Xiang has two other surviving offspring besides Bei Bei: Tai Shan and Bao Bao.