Beijing, China (CNN) -- Two of the world's most famous pandas received a celebrity's welcome in China Friday after being shipped from the U.S. aboard the aptly named FedEx Panda Express.
Amid tight security, throngs of photographers fixed their lenses on Tai Shan, 4, and Mei Lan, 3, as they arrived in Chengdu, China after a 15-hour journey.
They were returned to China as part of a longstanding agreement between China and the U.S. Under the deal, China retains ownership of adult pandas and any offspring, which are to return to China when they reach two years old. While Tai Shan and Mei Lan were born in the U.S., their parents are Chinese.
After the welcoming ceremony in southwest China, Tai Shan and Mei Lan will part ways. They will both enter one month of quarantine to allow them time to adjust to their new home and bamboo diet.
On clearing quarantine, Tai Shan will be taken two-and-a-half hours to Wolong's Bifengxia Panda Base, just outside the city of Ya'an. Mei Lan will be driven to the Chengdu Research Base of Giant Panda Breeding in Chengdu.
According to panda conservation expert Dr. Lu Zhi of Peking University, the timing of the intercontinental move comes at an appropriate time.
"It's a change. Animals need to adapt, but this is the right age to change," Lu told CNN.
Adapting to life in Sichuan will require some adjustment. Mei Lan will be assigned a Chinese tutor to teach her commands in Sichuan dialect, while Tai Shan will be immediately immersed in Mandarin.
The pandas' new responsibilities will include breeding future generations of pandas as part of efforts to conserve the species.
The public is already voting online for a suitable partner for Mei Lan. As of Thursday afternoon, panda Yong Yong held a comfortable lead.
Tai Shan and Mei Lan have already accomplished a lot for young pandas. During their time in the U.S. they won fans well beyond the borders of their respective zoos. A YouTube video of cub Tai Shan's sneeze got more than 51 million hits and counting.
Upon their arrival in Chengdu, U.S. Consul General David Brown praised the pandas diplomatic achievements.
"Ever since Tai Shan was born in Washington, D.C. in 2005, and Mei Lan in Atlanta, Georgia in 2006, both pandas have become endearing goodwill ambassadors for China in the United States," Brown said. "They, along with their parents and the other pandas on loan from China...occupy a special place in the U.S.-China relationship, which has matured and expanded over the past 30 years."
Their arrival in Chengdu comes amid frosty relations between the United States and China.
Tensions between the two have recently escalated over various issues, including Washington's plan to sell weapons to Taiwan, which Beijing considers a renegade province. China has threatened sanctions on American companies involved in the arms sales.
In recent weeks, the two countries also have traded sharp words over China's Internet policy, after the search engine company Google threatened to pull out of China, citing censorship and hacking attacks.
China is also fuming over plans by U.S. President Barack Obama to meet the Dalai Lama. Beijing accuses the Dalai Lama of advocating for Tibetan independence from China.
China's history of giving pandas as diplomatic gifts to other countries dates back more than a thousand years.
During the Tang dynasty, the Chinese gave the first set of pandas to the Japanese emperor.
In 1972, after President Nixon's historic visit to China, Mao Zedong sent the first set of pandas to the United States.
In the mid-80s, China decided to stop giving pandas away, instead choosing to loan them in exchange for millions of dollars that would be used in panda conservation efforts.