Mei Xiang might be pregnant—or not.
The National Zoo says it's on 24-hours-a-day panda watch as a female giant panda shows behavioral changes consistent with a pregnancy or pseudopregnancy.
Volunteer behavior watchers have been monitoring Mei Xiang via panda cams all day and night since Aug. 7. Keepers say Mei Xiang is very lethargic, eating less and shredding bamboo for her nest. Zoo officials say the panda sometimes cradles and grooms her toys.
Keepers say the behaviors have been seen every year during this time, and could either indicate that she's pregnant or suffering a pseudopregnancy.
The National Zoo's resident female panda gave birth to a cub in September 2012, but it died after only a week due to lung and liver damage. Before that, Mei Xiang produced Tai Shan—affectionately known as "Butterstick" after his size at birth—in 2005. She has also had five failed pregnancies.
Veterinarians have tried, but failed, to perform ultrasounds.