The surprise birth of a panda cub over the weekend at the Smithsonian National Zoo in Washington, D.C., was cause for celebration, but also some concern.
Panda cubs are born hairless and helpless, the size of a stick of butter and 1,000 times smaller than their mothers - human infants are 20-30 times smaller.
Even if they aren't accidentally crushed by their parents, the tiny cubs are also at risk for infections. The zoo is cautiously optimistic this one will make it.
"This first week we are at 100 percent attention, watching to make sure she's taking care of her cub," said curator Brandie Smith of panda mom Mei Xiang.
"Every week that passes we become a little more confident."
The baby panda cub, who weighed just five ounces at birth and arrives with its eyes closed, will not be named for 100 days, in keeping with Chinese tradition.
Panda breeding is difficult, in captivity and in the wild.
Zoo Atlanta has had three cubs, and the San Diego Zoo has had six, including a cub born this year. A panda couple in Memphis has yet to have a cub.
No other U.S. zoos have pandas. All cubs born are considered property of China - the only place they roam free - and on loan to the U.S. for sizable annual fees.