After housing giant pandas for a quarter-century, Zoo Atlanta in Atlanta, the U.S. state of Georgia, announced on Friday that its four iconic black and white bears will return to China in mid-October, in tandem with the expiration of the zoo's giant panda agreement with China at the end of that month.

"While Zoo Atlanta will certainly miss Lun Lun, Yang Yang, Ya Lun, and Xi Lun, and their departure is bittersweet, they have created a momentous legacy here in Atlanta and around the world, leaving their mark not only in the hearts of their friends and fans, but on the scientific and zoological communities' understanding of the behavior, biology, and care of this rare and treasured species," said Raymond B. King, president and CEO of the zoo, in a press release.

This year marks the 25th anniversary of the Zoo Atlanta giant panda program.

"Dating to the mid-1990s, even prior to the arrival of Lun Lun and Yang Yang in 1999, Zoo Atlanta's partnership with colleagues in China has a longtime history of collaboration and information sharing that has benefited the care, study, and conservation of giant pandas," the zoo noted in the press release.

Zoo Atlanta said its panda cooperative conservation program has been notably successful in terms of future contributions to the population of the species.

Seven giant pandas have been born at the zoo since 2006, including two pairs of twins. The offspring of Lun Lun and Yang Yang are Mei Lan (born 2006), Xi Lan (born 2008), and Po (born 2010); twins Mei Lun and Mei Huan (born 2013); and twins Ya Lun and Xi Lun (born 2016).

Mei Lan, Xi Lan, Po, Mei Lun, and Mei Huan already reside at the Chengdu Research Base of Giant Panda Breeding in China and have since all become parents themselves, according to the zoo.

The zoo will host a big farewell event on October 5 with special activities bidding the giant pandas farewell. Prior to their departure, the beloved bears will be viewable at the zoo's Arthur M. Blank Family Foundation Giant Panda Conservation Center.

Zoo Atlanta, which attracts around one million visitors each year, is home to more than 1,000 animals representing more than 200 species from around the world, many of them endangered or critically endangered.

The four giant pandas at Zoo Atlanta were once the only members of the rare species in the United States before the arrival of two Chinese pandas in California in June, which marks a new round of giant panda protection cooperation between the two countries. Yun Chuan and Xin Bao, the first to enter the United States in over two decades, made their eagerly-awaited public debut at San Diego Zoo on August 8.

Giant pandas are one of the world's most endangered species. Nearly 1,900 pandas now live in the wild, mostly in the provinces of Sichuan and Shaanxi in China, up from 1,100 in the 1980s.