population. giant panda cubs in u.s. zoos go to a breeding program in china once they turn 4. bei bei born here, and for years now, we've been reporting on him, a growth chart right in front of our eyes. laurie thompson, on the right, was one of the first to hold bei bei, and she's traveling back with him. >> i'm going to be going with bei bei to china. and on the plane, i'm just going to make sure that he's well fed and that he's happy in his crate. >> reporter: a specially designed crate just for him. plenty of bamboo to eat on the way. >> it's going to be really hard to say good-bye. and for me, i'll be the last one of the group to say good-bye to him, so, i'm sure once that really hits me, i'll probably have a little cry. >> reporter: and today, after bei bei left, the workers at the zoo hugging. a lot of hard work and love from that team. safe travels. i'm david muir. i hope to see you tomorr every few hours it seems