Clearly, red pandas are on a tight energy budget for much of the year. Not surprisingly, they have several strategies to help make energetic ends meet. Pralad Yonzon, working in Nepal, and Ken Johnson, George Schaller, and Hu Jinchu, working in China, found that red pandas spend as much as 13 hours a day searching for and eating bamboo. In contrast to the giant panda, which Johnson's team also studied, red pandas are very selective about what part of the bamboo plant they eat. The red panda selects only the tenderest young leaves and shoots and thoroughly chews each mouthful to increase digestibility.
Giant pandas eat virtually every part of the bamboo plant except the roots and barely chew at all.
Brian McNab, a physiological ecologist working with National Zoo animals, discovered that to cope with a low-energy diet and cool environmental temperatures, red pandas have evolved an extraordinarily low metabolic rate, expending almost as little energy as a sloth. They also are able to temporarily lower their metabolic rate even more at very cold temperatures. A tight energy budget driven by the reliance on low-energy food also influences reproduction in the red panda. Reproduction is energetically expensive, so red pandas reproduce in the late spring and summer when tender, more digestible bamboo shoots and new leaves are available and temperatures are warmer. John Gittleman and I, working with the National Zoo's red panda collection, found that although food energy is more available during gestation and lactation, red pandas still produce small litters, averaging just two cubs each.