Liu Yu, a researcher at Wolong National Natural Reserve, one of China's three research and conservation centers for giant pandas, said cooperation has proved effective.

"Mei Xiang and Tian Tian are the second pair of giant pandas at the US National Zoo in Washington. Under a cooperative research and breeding agreement, we have been working with US scientists to improve semen cryopreservation technology with the aim of raising the fertility rate of giant pandas," said Liu.

Mei Xiang, one of two pandas on loan to the US National Zoo in Washington, gets to grips with a slice of frozen fruit. Fang Zhe / Xinhua

He explained the rental procedure: First, a foreign zoo has to contact the China Wildlife Conservation Association and provide evidence and the necessary certificates to guarantee a safe and healthy stay. The association will then relay its assessment of the bid to a higher body, the Forestry Administration of China.

Next, a high-level Chinese politician will discuss the matter with a foreign counterpart. If a deal is struck, the association will select the pandas from three major habitat areas, including Wolong Natural Reserve.

"There is a line we never cross when choosing pandas; core species - those that have lived in the wild - won't be chosen, because we have to monitor their life patterns and they are extremely valuable to our own research and preservation," said Liu.

"We only send 'good-looking' pandas to foreign zoos. The judges have to decide whether the panda's 'shoulder strap' is robust and whether the dark, circular markings around the eyes are large enough. Also, if we loan a pair of pandas, we have to ensure they aren't closely related."

Once a lease agreement has been signed, the pandas are transferred to the destination with the utmost care, usually by FedEx, a courier service with wide experience of transporting the animals.

"When we receive a request to transport pandas, we provide a unique, customized solution to show our capability in shipping the cargo," said Tony Zhou, corporate communications manager at FedEx Express.

The most recent case of international panda transport took place in March. Two pandas, Damao and Ershun, were carried from Chengdu in Sichuan province to Toronto, the first time since 1985 that pandas have visited the city's zoo.

The members of the FedEx flight crew on the specially decaled MD 11F Freighter, the "FedEx Panda Express", were specifically chosen because of their experience of transporting large animals. An experienced loadmaster also traveled with the pandas to ensure the animals boarded and disembarked safely.

Before the flight, shipping enclosures were constructed to ensure safe and easy handling. The enclosures were 198 cm long, 142 cm wide and 137 cm high, and weighed approximately 360 kilograms. They had removable side panels to allow the attendants easy access to the pandas. The enclosures were placed in the pandas' habitat a few days before the flight to ensure that the animals had become accustomed to them before departure on March 25.

Ershun and Damao each had their own enclosure. Indeed, they were the only cargo on the plane. The spacious containers provided the pandas with plenty of room to move around and plexi-glass insets allowed them to see what was happening outside their enclosures. Necessary foodstuffs were also transported, including staples such as fresh water, bamboo shoots, and apples.

"For the flight, FedEx had a loadmaster with five panda shipments under his belt, including the first ever FedEx panda flight back in 2000. A veterinarian and two attendants had access to the pandas at all times during the flight. With their food stores and a comfortable cabin temperature, the pandas must have had an enjoyable journey halfway across the world," said Zhou.

Police escort

Upon arrival in Toronto, the pandas were escorted by police escort from the airport direct to the zoo. Damao and Ershun will stay in Toronto for five years before moving to Calgary Zoo for a further five years.

FedEx said the panda delivery service is free, and the company feels honored to be called upon to ensure safe passage, thus indirectly helping with the efforts to save the endangered species.

But while these measures have clearly helped to elevate the brand image overseas, the foreign zoos are also well aware that their efforts will be rewarded by a constant stream of visitors.

In 1999, the arrival of the Yangyang and Lunlun gave Zoo Atlanta an international reputation overnight and the visitor numbers rose by 60 percent.

"When the pandas arrive in a new country, our research staff will stay at least six months to record their mating behavior, eating habits, exercise preferences, sleep patterns and other characteristics. These detailed studies and research findings are always shared with our foreign counterparts," said Wang.

The plight of the pandas is a cause celebre worldwide, of course, but nowhere more so that in China and the most-famous recipient nation, the US. According to NetEase, one of China's main Internet portals, by October, the China-US Panda Workshop in Beijing had trained nearly 1,300 panda conservation professionals, with 100 of them traveling to the US to work alongside their US counterparts. Meanwhile, every zoo in the US has invested an average of $614,000 in research and education programs.

Contact the writer at zhanglei@chinadaily.com.cn

He Na contributed to the story.