Pandas roam to find better bamboo

By Signe Cane 25 July 2014
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Giant pandas strike nutritional balance in their diet by migrating to find different types of bamboo

PANDAS INFAMOUSLY SURVIVE on a very limited diet of 2 species of bamboo and it has baffled scientists as to how the mammals survive on such a nutritionally poor diet.

Now, new research from China and Australia has shown that giant pandas (Ailuropoda melanoleuca) are willing to wander far and wide in order to get the nutrients they need.

“Pandas need to migrate between different habitats in order to balance their diet for reproduction,” says study co-author Prof David Raubenheimer, a nutritional ecologist at the University of Sydney.

Pandas travel to vary their bamboo diet

Six pandas were tagged with GPS collars at the Foping Reserve in the Qinling Mountains, about 200km from the city of Xi’an in China. The region is a key conservation area with a high density of wild giant pandas.

The researchers tracked the pandas for six years, noting foraging and mating habits, as well as analysing samples of their food and dung. The results were published recently in Functional Ecology.

When spring comes in the Qinling Mountains, pandas move from the valleys to higher up into the mountains, and then trek back down in autumn. This annual migration cycle was mystifying until researchers started examining the kinds of bamboo pandas eat in these different areas.

At certain times of the year pandas switch to eating either the shoots or leaves of two bamboo species – wood and arrow.

During summer pandas look for bamboo shoots rich in protein, available at higher altitudes. However, this leaves them deficient in other aspects.

“Levels of calcium available in their food in summer are so low they must be drawing on calcium in their bones,” David explains.

To supplement the missing mineral which is vital during breeding season for bone support and lactation, pandas descend back into areas where calcium-rich bamboo leaves can be found.

Thus the seasonal foraging cycle is a smart strategy for maintaining the nutritional balance that allows pandas to stay healthy and make babies.

“The general picture has always been that bamboo is a low quality food for pandas, but that’s not strictly speaking true,” says David. “They’ve adapted to eating it.”

A giant panda munches on some bamboo leaves at the Bifenxia Panda Reserve in China. (Credit: Carolyn Barry)

Pandas threatened by habitat loss

While these endangered bears still have a digestive tract characteristic of their carnivorous relatives, their highly specialised bamboo diet became advantageous at a time when forests were abundant and hunting prey actually took more effort than sitting around and munching on leaves all day, David explains.

Currently the population of wild pandas is estimated at 1600, and they are struggling to maintain their diet in the face of environmental changes affecting the availability of the two bamboo types.

David emphasises that an understanding of the pandas’ seasonal nutritional demands at different habitats is critical for better protection of the species.

“In terms of conservation, it means that both seasonal foraging areas need to be preserved.”