On his first birthday Thursday, giant panda cub Mei Sheng (search) delighted visitors by playing for the first time in snow delivered to him at the San Diego Zoo (search). He also sat on his ice cake, wrestled with his mom, got his coat incredibly dirty, and didn't read any of the more than 700 birthday wishes sent him via e-mail from as far away as Ireland and Argentina.

His guests still couldn't resist him.

"Darling!," exclaimed Erin Anderson, who was visiting with her three children and their grandma. "Isn't he cute?"

The cub has become quite a little celebrity since his birth a year ago. He is only the second panda born in the United States to survive to his first birthday. Mei Sheng's half-sister, Hua Mei (search), celebrated the same milestone in 2000.

But researchers at the San Diego Zoo say Mei Sheng, whose Chinese name means "Born in the U.S.A." as well as "Beautiful Life," has been a very different baby from his half-sister.

For starters he complained more and was more demanding. He was also a little shyer -- preferring to stay close to his mom, Bai Yun, rather then venture out of the den.

"It just underscores the need to not generalize about an animal like this until you have a very robust sampling," said Doug Lindburg, the zoo's giant panda team leader.

On Thursday, Mei Sheng exhibited some of that shy behavior-- at first hiding behind a bush and sniffing tentatively at the snow when he found his habitat turned into a winter wonderland. Quickly, however, he followed his mother's lead and started clawing snow off the trees and delighting visitors with belly slides and gymnastic attempts that left him sprawled on his back.

In 12 months, Mei Sheng has grown from a 4-ounce newborn the size of a stick of butter to a 54-pound fur-ball. He's learned to walk and to climb trees. He's still nursing, but he is eating apples and carrots and bamboo leaves, said senior giant panda keeper Kathy Hawk.

He has also endeared himself to the public and to keepers, who call him their "Baby Boy," "Mr. M" and "Goof-ball." Oh, and "Pooper," which he responds to.

Hawk said next year is a big year for Mei Sheng, too. He'll likely be weaned, start eating the more solid parts of bamboo, and be separated from his mother, mimicking the separation process that goes on in the wild.

He's also working on kicking the shy thing

Thursday he seemed well on his way, charming visitors with his frolicking.

"Today they're putting on a really good show," said regular visitor Joan Grant, who came decked out for the celebration in everything panda: earrings, T-shirt, watch, socks, and necklace.

Judy Trest couldn't resist the pandas either, taking more than 300 pictures on her digital camera. And, the cub's enclosure was punctuated with frequent "oohs" and "awws." The line to see him stretched out of the exhibit.

"He's cute. I want to hold him," said Nicole Boyd, 13, who was visiting from Sacramento.

Zoo officials say Mei Sheng is more than cute, however. They say they attach great significance to the fact that another cub has survived to his first birthday. Only about 1,600 pandas are thought to live in the wild and about 170 in captivity, most in China, according to zoo officials.

In the United States only four zoos have pandas -- San Diego, Washington, D.C., Atlanta, and Memphis, Tenn. All the pandas are on loan from the Chinese government, which owns the adult pandas and any offspring. Any cubs born in the U.S. are supposed to be returned to China when they turn 3-years-old.

Under that agreement, San Diego's first panda Hua Mei went to the Wolong Giant Panda Protection Research Center (search) in southwestern China earlier this year, and there are hopes she is now pregnant. Mei Sheng would technically go back to China in two years, but zoo officials say they are hopeful he will be allowed to stay longer because China's breeding program is going so well and there may be less public pressure to send the second U.S.-born panda back.

More than hoping to keep Mei Sheng, however, zoo staff say they hope their success at panda breeding will spread to other zoos and that the panda population will grow.

For now, however, giant panda team leader Lindburg said, "There's one more panda in the world."