Veterinarians at the national zoo are waiting to find out if their female panda, Mei Xiang, is pregnant.
Pandas are fertile for just 24 hours --- once a year. so when one of the 4 female pandas in U.S. zoos gets pregnant, it's an exciting time for the zoos.
Giant pandas are extremely endangered and there are only 11 pandas in captivity in U.S. zoos.
Senior Curator Brandie Smith says, "This year her behavior seems to be a lot stronger than in previous years. She's building a huge nest and cradling toys. So this year we're a little extra hopeful that she may be pregnant."
If Mei Xiang is indeed pregnant, she is expected to give birth in the next three weeks.