Zoo staffers found the cub dead on Monday, and a necropsy showed it suffered "head trauma," though veterinarians were unable to say how it happened.
The three male cubs were born Aug. 6. The zoo, however, did not announce the births until yesterday, because they wanted to wait until it looked like they would be OK.
Zoo officials sought to dispel any notion that the cub was killed by its mother.
"The cub's mother, Lulu, has previously raised a total of five cubs in two successful litters in 2005 and 2007.
Sumatran tigers are an endangered species, according to the International Union for Conservation of Nature. Like most cats, tiger cubs rely largely on their mothers' care for their first year of life, Bernabe said.
"Every birth of these tigers in a zoo is significant and not without risk," she said.
The cubs have not been part of a regular zoo exhibit, but officials hope
to put the surviving two on exhibit by December. Videos charting the progress
of the cubs are available http://lazoo.org/animals/new/tigercubs.html.