A panda born at Atlanta's zoo and returned to China for breeding will end up being a father, not a mother as originally thought.
Zoo Atlanta staff and a researcher from the panda research centre in China where Mei Lan now lives examined the panda 19 days after its birth and determined the panda was female, said Rebecca Snyder, curator of mammals at Zoo Atlanta.
But researchers in China recently noticed male reproductive organs and determined Mei Lan is male.
It is difficult to determine the sex of giant pandas early on and mistakes are not uncommon, Ms Snyder said.
Generally, the Chinese try to examine cubs within a day or two of their birth because they are slightly dehydrated and have less fur, which makes a close examination of the genital area easier, she said.
"With Mei Lan we waited quite a while before we took him the first time because that was Lun Lun's first cub and she was doing a really good job taking care of him and we didn't want to risk disrupting her behaviour," Ms Snyder said. "So we waited until Lun Lun was leaving him regularly before we did the first exam."
A male panda's testes generally descend after he is three years old, but before that there are few obvious signs of gender, Ms Snyder said. That happened in Mei Lan after he had departed for China in February 2010.
Ms Snyder said she is not aware of any name change planned for Mei Lan, whose name means Atlanta Beauty.
Plans for Mei Lan would not have been any different had they known he was male - Zoo Atlanta's agreement with China requires that pandas be returned at three years old, and Mei Lan would still have gone to Chengdu Research Base, the same facility where he now lives.
"He's still valuable genetically," Ms Snyder said. "He'll just be a dad now instead of a mom."