ATLANTA (AP) — Zoo Atlanta officials say two giant panda cubs are being rotated between their mother and an incubator to ensure the newborn twins are properly fed and getting an equal amount of nurturing.

Lun Lun, a 15-year-old giant panda, gave birth to the cubs Monday. An ultrasound confirmed her pregnancy in June, but officials say they were unaware she was having twins until the second cub was born minutes after the first.

The cubs are the first giant panda twins born in the U.S. since 1987.

Zoo Atlanta's deputy director, Dwight Lawson, says both cubs appear healthy. But officials are taking precautions because of a high infant mortality rate among baby pandas.

Lawson says the cubs won't be named until they are 100 days old, in keeping with a Chinese tradition.