Beginning at 4 p.m. Friday, about 40 volunteers will rotate shifts, logging Mei Xiang's behavior. The zoo says they have already observed her spending more time shredding bamboo in her den to make a nest.
The Smithsonian's National Zoological Park is operating a webcam but limited access initially to five minues per session because of the expected crush of interest.
Zoo scientists have determined Mei Xiang's hormone levels are nearing baseline, which indicates the end of either a real or pseudo pregnancy. She was artificially inseminated in January.
Pandas' hormone levels and behavior can indicate they are pregnant when they're not.
Mei Xiang gave birth to her only cub, Tai Shan, in 2005. He was sent to a breeding program in China earlier this year.
About 1,600 giant pandas survive in the mountain forests of central China. More than 160 of the animals are found n zoos and breeding centers, mostly in China.
Ultrasound Tests for Fetus
Veterinarians have been conducting frequent ultrasounds to look for a possible fetus, but so far nothing has shown up, Korpowski-Gallo said. Panda fetuses don't start developing until the last weeks of a gestation period.
Mei Xiang seems to enjoy the ultrasounds and continues to cooperate. Panda curator Lisa Stevens wrote on a recent blog post that Mei Xiang plays with her belly after the ultrasounds.
"The ultrasound gel makes her double over and rub her belly and ears vigorously, exhaling with pleasure," Stevens wrote on Wednesday. "Rolling on her back reminds one staff member of a breakdancing back spin as she scent anoints her body with the gel."
In the final days of her 2005 pregnancy with Tai Shan (TY-shawn), though, Mei Xiang wanted nothing to do with the ultrasounds, zoo keepers have said.
Tai Shan, the zoo's only cub that has survived, was sent to a breeding program in China earlier this year.
An online panda cam fixed on Mei Xiang will allow the public to view the possible birth, but the zoo warns each viewing will be limited to five minutes because of heavy traffic expected on the site.