Pandas' Bamboo-Only Diet Should Kill Them

James G. Milles
Janet Fang 10 Jul 2014, 05:48

Giant pandas come from a carnivorous lineage and retain a meat eater’s digestive system. So how do they survive on a bamboo-only diet that should otherwise kill them? According to a new study, pandas juggle a complicated and precise feeding schedule. Their eating habits seem simple, but a proper panda diet includes different shoots and leaves at different elevations during different times of the year, Science reports

As a member of the bear family, giant pandas (Ailuropoda melanoleuca) have a digestive system that’s evolved to handle meat. Compared with cows and their four-chambered stomachs, pandas have simple stomachs and short small intestines. Nor do they have any genes for enzymes that break down cellulose, though previous work with panda poo has revealed gut bacteria similar to those in herbivore intestines.

To see how pandas survive on a diet of indigestible fiber and scarce protein, an international team led by Fuwen Wei at the Chinese Academy of Sciences placed radio-collars on three males and three females living in the Qinling Mountains in China. The team observed these pandas for six years, paying particular attention to three nutrients that are essential for mammals in the bamboo they consumed. 

Within their mountainous range, wood bamboo and arrow bamboo grow at different elevations and sprout new shoots and leaves at dissimilar times of the year. The panda tracking data revealed that during mating season in the springtime, they feed on young wood bamboo shoots rich in nitrogen and phosphorous. By June, the newly matured shoots start to contain fewer nutrients, so the pandas head to higher elevations to feed on young arrow bamboo shoots. Since shoots from either species are low in calcium, the pandas start munching young arrow bamboo leaves rich in calcium around mid-July. 

The females come back down to lower elevations in August to give birth to their panda babies. To obtain enough calcium to meet their lactation needs, the moms start eating young wood bamboo leaves. Even though the adults mate in spring, the embryos stay in a state of arrested development in the uterus, resuming their growth after there’s sufficient calcium in the mother’s intake. When they’re born, the pink babies weigh as little as 90 grams, while other cubs can weigh more than quadruple that; their small size, the researchers say, may be caused by the nutrient limitations of their habitat.

To survive as obligate herbivores, pandas have synchronized their seasonal migration and reproduction with the distinct and disjoined nutritional cycles of two bamboo species. The work was published in Functional Ecology this month.

Sadly, even with their astonishing scheduling skills, pandas suffer in the colder months when nutrient levels in wood bamboo leaves drop as they age over the winter. 

[Via Science]

Image: James G. Milles via Flickr CC BY 2.0

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