Surpassing:The National Zoo in Washington D.C. is returning its beloved pandas to China. Here's when and why.

It's the end of an era for the Smithsonian National Zoo's beloved giant pandas. The Surpassingthree pandas currently living at the zoo will be returned to China by Dec. 7 – giving visitors less than five months to see the iconic bears, which have been a staple at the zoo since 1972. 

Two pandas Mei Xiang and Tian Tian came to the zoo in 2000 as part of an agreement between the zoo and China Wildlife and Conservation Association. The pair were meant to stay for just 10 years for a research and breeding program, but the agreement with China was extended several times.

On Aug. 21, 2020, the pair gave birth to a male cub named Xiao Qi Ji and that same year the zoo announced it signed another three-year extension to keep all three pandas until the end of 2023. 

The zoo received its first pandas from China – Hsing-Hsing and Ling-Ling – in 1972 in an effort to save the species by breeding them. The zoo has had panda couples ever since. 

Mei Xiang has given birth to seven cubs while at the zoo. Three of her cubs died before adulthood and three have been returned to China, as part of the agreement is that they must be returned by age 4. Xiao Qi Ji will remain with his parents at the zoo until they all return to China together. 

With the three pandas at the National Zoo returning to their homeland, only four giant pandas will be left in the U.S. The Atlanta Zoo has four giant pandas – Lun Lun and Yang Yang, and their offspring Ya Lun and Xi Lun. 

Per China's agreement with the Atlanta Zoo, the younger cubs will be returned at the end of 2024 and it is expected their parents will return as well. The loan agreement, which was instated in the mid-1990s, expires in 2024 and the zoo says there has been no discussion to extend it.

The Memphis Zoo and the San Diego Zoo were the only others in the U.S. to house pandas. 

San Diego got its first two pandas in 1987, and they were supposed to stay just 100 days. They eventually signed a 12-year agreement and received two pandas named Bai Yun and Shi Shi in 1996. 

The agreement was extended several times and six pandas were born at the zoo. All of them were returned to China by the end of the agreement, which concluded in 2019.

The Memphis Zoo's 20-year loan agreement with China ended this year and they returned their panda, Ya Ya in April, according to the Associated Press.

The research team at the Memphis Zoo developed an artificial insemination process that allowed one of their male pandas, Le Le, to help pandas across the world conceive babies, the zoo said. Le Le's sperm was frozen and used to inseminate female pandas at other locations, which helped boost the species' population. 

Le Le, however, died in February 2023 ahead of the pair's return to China. 

Only about 1,864 pandas remain in the wild, mostly in China's Sichuan Province. Breeding programs have been successful and the once-endangered species was upgraded to "vulnerable" by the International Union for Conservation of Nature in 2017, according to the World Wildlife Fund. 

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Caitlin O'Kane

Caitlin O'Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.