Giant panda twins Mei Lun and Mei Huan boarded a plane in Atlanta headed for Chengdu early Thursday morning, taking with them 375 pounds of bamboo, eight gallons of water and 25 pounds of treats — sugarcane, bananas and biscuits — for the 38-hour journey.

The 3-year-old twins born in the Atlanta zoo are the first surviving giant panda twins in the United States. They are the daughters of Lun Lun and Yang Yang, who arrived in 1999 on loan from China.

According to an agreement reached by the two countries, panda cubs born in the US to parents on loan from China are to be returned to China before turning four to take part in breeding projects.

After a layover in South Korea, Mei Lin and Mei Huan will arrive on Saturday at their new home at the Chengdu Research Base of Giant Panda Breeding, where their parents were born and their older brothers and sister, Mei Lan, Xi Lan and Po, now reside.

"This is a milestone to be celebrated," said Raymond B. King, president and CEO of Zoo Atlanta. "While the Zoo Atlanta family and their many fans will miss seeing Mei Lun and Mei Huan in Atlanta, we're very proud to see two more Atlanta-born giant pandas go to join such an important program."

"It's a tribute to the success of the Zoo Atlanta giant panda program and to the commitment of our international partners who are helping us save this species," he said.

Recently the International Union for the Conservation of Nature upgraded the giant panda's status from "endangered" to "vulnerable", but the species remains heavily reliant on conservation programs.

Fewer than 1,900 giant pandas are estimated to remain the wild in China's Sichuan, Shaanxi and Gansu provinces, where they face continuing threat from habitat fragmentation and loss from human activity such as deforestation. More than 1,200 of China's remaining wild giant pandas live inside nature reserves, many of which are supported by US zoos.

Once the twins leave, there will be 13 pandas still in the US — four in Atlanta (the twins' parents and their new sister twins born on Sept 3), four in Washington, three in San Diego and two in Memphis.

The National Zoo in Washington will be saying goodbye to its panda cub Bao Bao in 2017.

hezijiang@chinadailyusa.com