Buzzing with success over the first panda cub born at Zoo Atlanta, veterinarians were on birth watch Thursday for a possible twin sibling.
There's a 50 percent chance that Lun Lun, a 9-year-old giant panda from China, will give birth to another cub in the next few days, zookeepers said.
Twins usually arrive within 24 hours of their sibling, but Lun Lun was in labor for a record 35 hours, meaning a twin could pop out later than usua, reports AP.
"There's some sign there's another cub in there, but we just don't know," said Dennis Kelly, the zoo's CEO. "So we're trying to be really vigilant."
In the meantime, Kelly said that Lun Lun, a first-time mother, was bonding well with her new cub. The tiny hairless bear will not open its eyes for another 75 days, and its gender might not be known for weeks. At 100 days, the zoo is planning to present the cub to the public and hold a naming ceremony for it.
In many ways, panda births in the U.S. are still uncharted territory. The birth was the fifth giant panda born at a U.S. zoo in the last six years, and only about 75 births have ever been recorded.
Lun Lun's pregnancy proved a particularly difficult task. The zoo had tried to impregnate her for seven years, finally announcing at the end of March that she was successfully artificially inseminated with semen taken from her male partner, Yang Yang.
Determining if there's a twin could be equally challenging. The babies are about the size of a squirrel and weigh only four ounces (113 grams). As one zoo aide said, it is like trying to detect a stick of butter in a 237-pound (107-kilogram) bear.
Along with media publicity, baby pandas often bring a boost in ticket sales.
Annual attendance could jump from 700,000 to 1 million as the cub grows older, Kelly said. Indeed, excited visitors who received an e-mail alert about the birth Wednesday night were already lining up to see the proud papa, who sat atop a wooden platform, marking his territory.
"This is really exciting," said Jackie Roberts, who came to the zoo with her sister and 2-year-old son Benjamin.
The attendance boost, though, is only expected to be temporary. Kelly warned that the staggering cost of caring for the pandas makes it unlikely the zoo will keep them beyond 2009, when their 10-year contract with China expires.
It costs the zoo at least $2 million (Ђ1.57 million) each year to house the pandas, including $1.1 million (Ђ860,000) in loan fees paid to China, which owns the animals. If the zoo cannot negotiate a reduction of those fees by 2009, it might return the pandas to China when the agreement ends. "It's not financially sustainable," Kelly said.
As for the cub, it could be key to helping revitalize the panda's dwindling numbers, Kelly said. There are only 1,600 to 3,000 of the endangered species remaining in the wild today, and 185 living in captivity.
"You never know," he said. "This cub may be responsible for dozens of offspring."