The National Zoo announced Wednesday that one of the twin panda cubs born on Saturday had passed away. The twin is still in good health according to the zoo's director. The cub that passed away weighed merely three ounces while the surviving twin was 4.8. Zookeepers planned to switch the cubs every four hours to allow for the mother to nurture each one. In the wild, panda mothers often raise one cub and let another perish.