Appendix: Another animal that feeds on bamboo all year round:
One other species relies on the bamboo throughout the year: the aptly named bamboo rat, Rhizomys sinense. The genus Rhizomy's comprises three species, found from southern China westwards across Indochina to Assam, and southwards to the island of Sumatra. Around 40 cm long, it is covered in a dense, soft pinky-grey fur, with small, piggy eyes and the most enormous set of yellow-brown buck teeth'. The short legs bear large digging claws. The bamboo rat is rarely seen above ground, preferring to spend its time in the extensive burrow system each family group excavates for itself around and beneath the bamboo stands. Large mole-hills around 40-60 cm in diameter and the occasional wilted bamboo stem are the only physical evidence of the animals presence. One burrow system in the Choushuigou area of Wolong measured around 175 cm sq. The tunnels are about 15-17 cm in diameter, just enough to let the animals move easily through them, although they do widen in places to serve as nests (normally lined with bamboo leaves) and as latrines. The burrows lie some 15 cm below the surface. When excavated, the burrow systems are surprisingly extensive, with blind alleys and infilled older tunnels. There is anecdotal evidence that male and female bamboo rats may inhabit separate tunnel systems for most of the year.
The bamboo rats have developed specialized behaviour which they use to feed on their chosen food with the minimum risk from predators. They tunnel close to a bamboo clump and, while still beneath the surface, use their enormous incisors to snip a stem from the rhizome. They then lie on their back or side in their tunnel and use their front paws to lead the stem in to their continuously moving incisors, snapping away frenetically until most of the bamboo is consumed. From above ground, all that can be seen is the somewhat disconcerting sight of a bamboo stem sinking slowly beneath the surface of the earth. Very occasionally bamboo rats will venture out at night to snip off a bamboo stem, dragging it back to their burrow and stopping up the hole with stones and soil.
Whether the bamboo rat and giant panda compete for bamboo as a food resource is not so certain. But on the face of it, they must compete. They both eat stems, and stems would seem to be a finite resource. It has been pointed out, however, that the activity of the bamboo rat is somewhat analogous to the human gardeners habit of pruning blackcurrants and other soft fruit cutting out the old wood stimulates the plant to produce more fresh shoots. So the bamboo rat may unwillingly doing the panda a favour, thinning out the bamboo stands and stimulating the plant to produce more fresh shoots. This is probably true of the umbrella bamboo, whose shoots the giant panda finds particularly delicious.