ATLANTA (AP) — Zoo Atlanta officials say a pair of twin newborn Giant Panda cubs are gaining weight because they are nursing well with their mother.

The twin males born to Lun Lun and her partner, Yang Yang, are the first giant panda twins to be born in the U.S. since 1987. Lun Lun delivered the cubs Monday evening.

Rebecca Snyder, the zoo's curator of mammals, said in an update Thursday that they are thriving on their mother's milk.

Snyder said the cubs lost weight after the birth -- which is normal -- but gained weight steadily since then and are now nearing their birth weights. She said that's a good sign that they are healthy and will continue to grow and remain strong.