Giant Pandas in the wild are known to eat at least 26 different plant species, but this is not true. More than 99% of their food they consumed consists of bamboo, the umbrella and arrow bamboo. They eat 10 to 20 kg of bamboo each day, and spend 10 to 16 hours a day feeding. They gorge themselves on springtime shoots; and the proportion of leaves and stems consumed varies throughout the year.
Although the giant panda has some efficient adaptations in its body to facilitate digesting bamboo, most of the bamboos energy is not available to it. The pandas digestion of bamboo is almost suicidally inefficient. It is unable to digest cellulose and other structural carbohydrates in the bamboos cell wall, and with its short gut giving a low retention time to extract whatever nutrients are available from the plants cells. To compound the problem, the nutritional
content of bamboo is not very high (see table). Therefore, the giant panda has to consume prodigious quantities of bamboo to meet its daily nutritional requirements.
Some researchers weighted total daily droppings from wild pandas in Wolong. Using captive study giant pandas and other information, they are able to work out the amount of fresh bamboo a panda ate in any given time period. From their data, the amount of food giant pandas eat varies from day to day. In spring, when pandas start eating new umbrella bamboo shoots, one of their most favourite foods, the average weight of bamboo consumed rockets.
When feeding on succulent new shoot, the giant panda takes in more water than it needs; they rarely drink. At all other times of the year defaecation causes the elimination of more water than the giant panda can take in by eating bamboo. They are therefore constrained to drink one to four times a day. They do not eat snow to obtain water; they would lose far too much body heat to make this behaviour worthwhile.
The giant panda can easily climb trees like a bear, and yet nobody has ever seen a giant panda scaling an oak tree to eat those highly nutritious nuts. Some researchers reported that giant panda will walk quickly through stands if nutritious wild parsnip to feed on a nearby clump of much lower quality bamboo. No one knows why the giant panda does not eat those food that can make its life a lot less difficult (see Energy Budget), but it may be that the millennia which honed the pandas behaviour and physiology into a specialist feeder also withered the animals curiosity. The giant pandas brain seems only recognise two categories of plant in its environment: bamboo (=food) and other vegetation (= non-food). The other plants may actually be better for it does not seem to have ever crossed its mind.
Nevertheless, this fixation of food does not extend to animal protein. Given the pandas large bulk, low calorie diet, it is not surprising to find that the former carnivore has a taste of flesh. Following bamboo die-back in 1983 in the Qionglai Mountains, many pandas were lured to traps by mutton or goat cooking on open fires. The smell was apparently irresistible to them. Even in the absence of these human hand-outs, panda dropping do sometimes contain animal remains. Some researcher discovered the hair of golden monkey in one pandas droppings, and the hooves, bones and hair of musk deer in another. Villagers in Wolong informed researchers that they had seen a giant panda catch and eat a bamboo rat. It is a fact that giant panda are capable of quite a turn of speed when they put their mind to it, perhaps enough to run down a young musk deer or smaller mammals. Most remarkable of all, a few pandas can turn rogue. Once in Wolong Research Station, a female giant panda love to eat goat. Before it was being transferred to the research station she had managed to raid several farms and to kill and eat up to thirty-five goat and sheep.
The captive pandas food is more variable than the wild pandas. It is mainly due to not many zoos can supply enough bamboo to their giant pandas, especially the arrow bamboo from pandas mountain home. So, the zoos (in China) also feed their pandas with bottles of milk, eggs plus other fruits, and also corns, Gaauliangmi (rice) and Wowotou (bread).