Pandas belong to the Ailuropodinae, the oldest family of the most primitive lineage of bears.  Fossils of the oldest ancestral panda, Ailuropoda lufengensesis, are about eight million years old.  These fossils were found in southern China.  The earliest pandas were small, forest-dwelling creatures for millions of years until about the time of the late Pliocene three million years ago, when larger pandas developed.  Pandas about half the size of modern giant pandas, Ailuropoda microta, were widespread throughout southern China about 600,000 years ago and were replaced by a larger species, Ailuropoda melanoleuca baconi, that was even larger than the modern giant panda.  The modern giant panda evolved during the late Pleistocene.  The fossil evidence suggests that in the late Pliocene and early Pleistocene, some 2 to 3 million years ago, the ancestral pandas were widely distributed over much of eastern and southern China as far north as Beijing.  They ranged into what is now Taiwan, northern Myanmar (Burma) and northern Vietnam.

During their long evolution, pandas adapted to exploit the widespread and reliable plant resources of southern Asia.  As they did so they lost many of the carnivorous and omnivorous traits of their ancestors and developed specialized adaptations for feeding on plants.  One of the most stable food plants, for hundreds of thousands of years, has been bamboo.  Recent ancestors, and the giant panda in particular, became increasingly dependent upon bamboo as a sole food source.  Although bamboo can only be partially digested, and there are other more nutritious foods available, bamboo was apparently a constant and reliable source of food through changes in climate and changes in season.   Evolution favored reliability at the cost of variety; but even bamboo in its many species provided ample variety.  The major drawback for thousands of years was that most of a panda’s time awake had to be spent feeding.   A more serious drawback arose as human populations expanded.  Specialization reduces options, and as the bamboo forests disappear the pandas are unable to adjust to other food sources.  Omnivorous food habits have been the successful strategy of almost all the other bears, but the pandas lost that strategy and can never get it back.

Like the other tropical bears, the early pandas were evolving in competition with other efficient predators, primarily the large cats.  Unable to compete for prey species, and being preyed upon themselves, the early pandas evolved specializations in the direction of tree-climbing and the utilization of plant foods.  We don’t know what their diets consisted of, but the ancestral pandas were likely not as specialized in diet as the giant panda.  Giant pandas forage almost exclusively on bamboo.  There are a few records of pandas eating other plants or occasionally utilizing carrion such as deer, but about 99 percent of the diet consists of the stems and leaves of bamboo.

Despite bamboo’s poor digestibility, the security and reliability of the bamboo forests enabled the giant panda to specialize on bamboo as its sole source of food.  When food became scarce in one area, pandas could move to another area where it was plentiful.  Bamboo would still be a stable food source except for the rapid expansion of humans in southern Asia and the development of agriculture.  As humans increasingly dominated the landscape the giant panda was forced to retreat.  Today only about 1000 giant pandas remain.  They live in six remote and isolated mountain regions and spend the summer in higher elevations above 2200 meters.  In these regions they live in temperate montane broadleaf forests and broadleaf/conifer mixed forests up into the subalpine conifer forests.  Bamboo species are common in these forests and are often the dominant form of vegetation.   There may be as many as 33 species.  However, they are primarily small or dwarf species less than 5 meters in height, and only about 15 species are widely available and preferred.  Even the best of this habitat is marginal in relation to what pandas need and what was once available to them.  There was a severe bamboo die-off in the late 1970's and early 1980's during which many pandas had to be rescued from the wild as they neared starvation.  In the Min Mountains 138 pandas were found dead during this period by one rescue team.   The rescued pandas and their offspring survive in zoos.

Pandas move up and down in elevation during different seasons in order to select certain bamboo species.  The growing shoots are most nutritious. Once the shoots are fully grown they become tough and fibrous and pandas move upward in elevation to where emerging shoots of other species are available.  They continue to eat new shoots as long as they are available and then concentrate on leaves during summer when they are most numerous.  In winter they rely more on stems and whatever leaves are not dead.  In the winter they generally depend on lower areas, between 1200 to 2000 meters, where they also mate and give birth.  This lower elevation habitat is particularly threatened by the continued expansion of the human population in China.

Some links with more information on pandas include:

• GeoZoo
• The Bear Den
• WWF Factsheet
• San Diego Zoo and PandaCam
• Etling Panda site

Picture courtesy of Harriet Corbett, Rox Graphics, 866 Rd. 7RP, Powell, WY 82435, 307 645 3202, crowhart@wtp.net