The National Zoo in Washington announced Friday the surviving cub born to resident pandas Mei Xiang and Tian Tian last week is male.
Mei Xiang gave birth to fraternal twins last Saturday, but the smaller cub — also a male fathered by Tian Tian — died on Wednesday.
Zoo official Wendy Smith told reporters the surviving cub is thriving.
"Best of all, what we see is when the cub squeals, Mei pays attention," said Smith. "So we know she's taking care of it. She's nursing. I mean, she's been in that den since she gave birth, so not going out to urinate, to defecate, to eat anything. Today, all these days later, even as she tried to make her way out, squeals from that cub brought her right back. It took her a few tries to get out."
Officials say the deceased cub was examined by the staff. They say the most likely cause of death was complications associated with aspiration of food, resulting in the development of pneumonia.
Keepers say the surviving cub is doing well, gaining weight and growing.
The twins' birth captured international attention as giant pandas are among the world's most endangered species. Mei Xiang was artificially inseminated with sperm from Hui Hui, a panda in China and from the National Zoo's Tian Tian.
Giant pandas, native to China, have a very low reproductive rate, especially in captivity. There are about 300 giant pandas in captivity and roughly 1,600 in the wild.