Panda cam star Bao Bao's bittersweet rite of passage

The 18-month-old panda cub Bao Bao is leaving her mother Mei Xiang to live on her own.

It may be hard for us humans -- especially mothers -- to understand, but that's how it happens in the wild, and so the zoo is following nature, reports CBS News correspondent Jan Crawford.

Last week they spent nights together, but their days apart -- Bao Bao in one yard, mom in another.

"This is a natural thing. Mama's not sad at all. It may be more of an adjustment for the cubs but we do know they get past it very quickly," said panda keeper Nicole MacCorkle at Smithsonian's National Zoo.

In the wild, panda cubs usually leave their mothers for good at about the age of two.

The zoo says the early signs of separation were obvious.

"They spend less time together. They have less interest in each other. And it's a little bit sad to us. But we watch Mei Xiang, and when Bao Bao comes over to nurse, Mei will push her away," National Zoo senior curator Brandie Smith said. "She's like, 'you're a grownup now. Go, you know, eat your own bamboo.'"

That was another sign; when Bao Bao started eating solid food, like bamboo and sweet potato. And her training was improving.

CBS News cameras watched as Bao Bao followed commands inside a cage used for drawing blood from adult pandas. She's asked to stretch out her arm and squeeze the metal rod. She gets close.

For panda fans everywhere, Bao Bao is a star, her life documented on the Panda Cam.

From her earliest days, we've watched Bao Bao learn to crawl, get checkups and play outside with the occasional tumble.

The video of her first snow day has more than 5 million hits on YouTube.

"We've noticed that Bao Bao is definitely more independent and she's been more independent since the day she was born. And it's actually great because the weaning process is going so quickly, so simply," Smith said.

Timing is critical. It's breeding season for pandas and Mei Xiang will only be fertile one to two days. If Bao Bao is still around, there's a chance Mei won't breed.

It's nature's explanation for why mother and cub must separate, but the finality is challenging for human emotions.

"The world changes when you are a parent and you see things differently. But we're parents of little humans and Mei Xiang is a parent of a little panda and this is the stage where the little panda needs to go and be a big panda," MacCorkle said.

"We are taking our cues from Mei. Mei is telling us that it's time for Bao Bao to go. And we're letting that happen. We're helping her set Bao Bao off on her own," Smith said.

Bao Bao and Mei Xiang will continue to live in the panda house but when she turns 4 years old, she'll go to China as part of an agreement with the Chinese government and there she eventually will have cubs of her own.