SYDNEY, July 22, Xinhua - Scientists have made an important step toward explaining why China's iconic giant panda is such an obsessive eater - munching up to 15 kg of bamboo varieties everyday - with collaborators from the Chinese Academy of Sciences (CAS) and the University of Sydney, and it's all part of the panda plan.

Their findings, which were published Tuesday in the journal Functional Ecology, show that researchers now believe there is ' method to their madness', with the notoriously fussy eaters switching between different species and parts of bamboo plants to maintain a balanced diet and to reproduce.  

According to the research led by academics at the Chinese Academy of Sciences and co-authored by the University of Sydney's Professor David Raubenheimer, pandas will migrate vast distances to alternate between two different bamboo varieties and the particular nutritional properties they can provide.  

The four distinctive diets provide different levels of key nutrients, with shifts between the diets enabling the pandas to balance their calcium, phosphorus and nitrogen needs to successfully reproduce.  

"We were surprised to discover that pandas arrange their migratory and reproductive habits around the nutritional qualities of two specific bamboo varieties, arrow bamboo and wood bamboo," said Professor Raubenheimer, Chair of Nutritional Ecology at the University of Sydney's Charles Perkins Centre and a co-author of the research.  

The findings have profound implications for the conservation of China's wonderful national symbol, particularly given the accelerating environmental changes that threaten to transform the prevalence and location of the two bamboo species.  

"Pandas in the Qinling Mountains of China move from valleys up mountains in spring, and then move back again in autumn," Professor Raubenheimer said.  

There are more than 50 panda reserves in China, protecting 45 percent of the remaining giant panda habitats.   According to Jason Hakof, acting curator at Adelaide Zoo, a giant panda's diet is literally 99 percent bamboo. Some 13 kg or an average 3,500 bamboo stalks a day.  

Adelaide Zoo currently hosts Australia's current panda's Wang Wang and Funi, but Australians have been enthusiastic 'panda watchers' and its Zoos have had the honour to host giant pandas as residents from as far back as 1988 when Melbourne and Sydney's Taronga Zoo welcomed Xiao Xiao and Fei Fei, as part of a cultural agreement between Australia and China commemorating Australia's then Bicentenary.  

The giant panda has the digestive system of a carnivore, but has chosen to live almost exclusively like a vegetarian. Bamboo doesn't provide much energy, so giant pandas have to keep eating for up to 12 hours a day.  

"The summer forage contains high levels of protein, needed for muscle growth, but is very low in calcium, which is required for milk production and bone growth. By contrast, the winter forage has high levels of calcium but is low in protein.  

"It is only by migrating seasonally, therefore, that pandas can obtain enough of both essential nutrients to breed."   Adelaide Zoo has always been aware that pandas prefer to have variety in their diet, both in the wild and in captivity, says Adelaide Zoo's Alison Hassell.  

"Wang Wang and Funi have always showed that they prefer to consume different bamboo species and parts of the bamboo at certain times of the year. For this reason we try to always provide them with a variety of bamboo."  

In summer they tend to prefer more leaves and in winter, which is when they tend to bulk up, they prefer to eat the thick culm ( or stem) of certain species.  

Visitor numbers jumped more than 75 percent after Adelaide Zoo welcomed Adelaide's pandas in 2009 and the pair have become an important part of what makes Adelaide such a popular international destination.

"Our bamboo plantation grows 17 different species of bamboo to ensure that our pandas have the variety that they require. At any one time we hold four to five different species of bamboo in our specially designed cool room, within the panda building.  

Hassell said Adelaide Zoo is "always interested in any new research that comes out in regards to any animal that is within our care."  

"New research like this is a valuable tool which helps us continually improve animal husbandry and welfare practices."  

The CAS and Sydney University collaborators tracked six pandas in China's Foping Reserve with GPS collars over a period of six years, conducting behavioural and diet analysis during the four foraging cycles.

The nutritional balancing observed in the pandas is a key factor in the survival of the endangered species. Despite being exclusively herbivorous, the giant panda retains the simple stomach and short gastrointestinal tract of its carnivorous bear cousins. As a result, the preservation of its highly specialised diet is crucial to the continued existence of the species.  

"As this study has revealed, it is critical for us to understand the nutritional basis of food selection when managing endangered species. This is true not only for the giant pandas of the Qinling Mountains, but also, for example, for the highly endangered New Zealand kakapo parrot, spider monkeys in Bolivia and the wonderful mountain gorillas of Uganda," said Professor Raubenheimer.  

According to Sydney University, the study is the first to integrate 'nutritional geometry', pioneered by Professor Raubenheimer, which models diet-to-reproduction in the wild and has been used to analyze the feeding behaviours of many species, including mice, locusts, flies, spider monkeys, gorillas, grizzly bears and humans.