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Bei Bei the giant panda celebrates last birthday at National Zoo before China move

Washington — Bei Bei, a giant panda at the Smithsonian National Zoo in the nation's capital, turned 4 years old on Thursday, marking a bittersweet milestone that signals the end of his time living in the U.S. 

One of the zoo's fan favorites, Bei Bei's caretakers marked his birthday with a cake laced with all the trimmings: fruit juice, fiber biscuits, pears, bananas, carrots, sweet potatoes and a sugar cane topping. 

Born in 2015 to parents who will remain at the zoo, Bei Bei is the product of a breeding agreement between the Smithsonian and China that calls for offspring of adult pandas born in the U.S. to be transferred to China once they hit their 4th birthday. 

Spectators sang "Happy Birthday" as Bei Bei clawed into the frozen fruit and veggie concoction, made by the Zoo's Department of Nutrition Science.

Bei Bei's 4th Birthday by Smithsonian's National Zoo on YouTube

"His number one favorite treat is sugar cane," said Mariel Lally, an animal keeper at the National Zoo who works primarily with the pandas at the "Asia Trail" exhibit. 

"This is a very big cake for him," said Lally. Usually Bei Bei gets a small serving of about 24 ounces of frozen fruits a few times a week. The type of cake he enjoyed Thursday is reserved for birthdays.

According to Lally, Bei Bei's typical diet consist mostly of bamboo, and he eats about 60 pounds a day during the summer, nearly a quarter of his weight for the 244 lb. young panda. 

The zoo's panda habitat is home to Bei Bei's parents, Mei Xiang and Tian Tian. Both have lived at the Smithsonian National Zoo since December 2000. Bei Bei, their third surviving cub, has two older siblings who have both moved back to China in recent years. 

Because the offspring born in the U.S. eventually enter a breeding program, they move to China just before they hit sexual maturity. Back in China, the pandas help contribute to the panda population and support larger educational and conservation efforts

Bei Bei's parents are allowed to continue to live in the U.S as long the agreement is in effect. The current agreement expires in December 2020.

While there is no specific date for Bei Bei's departure just yet, the zoo is in talks about the logistics of how he will make the trek.  

"We're expecting sometime in the next upcoming months, most likely before the end of the year," said Lally.  

In the meantime, spectators have a least a few months to see Bei Bei before he heads overseas.

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