Appendix: Why does the giant panda have such an unusual behaviour?
Further study has revealed that the reason for this can, as with most aspects of the giant pandas activity, once again be laid at the door of the bamboo.
Because the bamboo is hard to digest, a panda must eat often to keep its alimentary canal filled and allow an uninterrupted flow of nutrients into its body. But a pandas gut has a finite capacity, and the animal can only eat so much before the digestive system is filled. The capacity of a giant pandas stomach is around 4.5 kg of bamboo, which happens to be the amount defaecated by a panda in five hours (bamboo travels the whole length of the pandas digestive tract in eight hours). So, any panda that sleeps more than fours hours will awake to a very empty stomach. Given the poor quality of the pandas diet and its need to maintain a steady trickle of nutrients into its system, an empty stomach is not the minor inconvenience it might be to most carnivores it is a matter of survival. This explains the animals need to work a shift of eight hours feeding and four hours sleeping through the day and night. The giant panda is quite literally constrained to feed around the clock.