her name means precious. here's tom foreman with the story. >> she's so warm. >> reporter: at just 17 pounds, 5-month-old bao bao is already a heavyweight in the world of conservation. >> 58 centimeters. >> reporter: a rare success in the long fight to preserve the giant panda. >> pandas are notoriously difficult to breed. >> reporter: ari thompson tends to bao bao and says there are many reasons. pandas are naturally solitary and usually don't mate well in captivity. artificial insemination is difficult and many don't make it. the panda's american journey, however, has been key to the species' survival.