The Wolong study involved only eighteen animals, a small population by any standards, but it is enough to give us some idea of the giant panda's population dynamics. The data are based on radio-collared animals and from direct and indirect sightings. Panda density in the 35 km square study area was about one animal per 1.9 km square, or one animal per 1.24 km square if considering only the twelve residents and only the 15 km square of Sinarundinaria bamboo where the pandas spent most of the their time. As a panda need only about 0.5 km square of Sinarundinaria to live on indefinitely, it is clear that the Wolong environment could actually support more than twice the number of pandas it does. In other words, food is not a limiting factor on panda numbers in Wolong.
Knowing the relative proportion of different age classes in a population is useful in assessing the health of a population whether it is stable, increasing or declining. Too high a proportion of young animals and too few adults of breeding age could indicate that there are not enough adults to sustain population levels. Equally, too few young animals indicates that the breeding adults are for some reason not producing young. Some researchers identified three age classes in the Wolong population of giant pandas: infants (birth to 1.5 years, the age at which they leave their mothers); sub-adults (1.5 years-5 years); and adults (5 years plus). The relative proportion of the Wolong age classes was two infants; four independent sub-adults; and twelve adults (seven males and five females). The fact that there were six animals below breeding age indicated steady recruitment in the Wolong population.
Available information is too sparse to say anything about the mortality rates of giant panda populations. Large carnivores of giant panda size, such as bears, live for about twenty to thirty years. Information on giant panda longevity is sparse as most toes have not kept giant pandas for this length of time, but one female in Beijing Zoo died around 30 years of age and another female in Nanjing Zoo lived for twenty-nine years. Pandas in toes outside China have a much shorter lifespan, seldom surviving longer than fourteen years.
There are many reasons for infant death, some of them due to the mother herself if conditions in captivity are anything to go by. One captive female crushed her offspring, while another partially ate one of her cubs soon after birth. In the wild, females have to leave their young unattended for long periods in order to feed and this means the little ones are open to attack from such predators as leopards, golden cats, yellow-throated martens and weasels. Even when infants are old enough to leave the den they are still small enough to be vulnerable to attack from the larger predators and this may be true even of sub-adults up to about 2 and a half years of age, weighing about 50 kg. Cubs, especially those still taking milk, may also starve if they become separated from their mother among the dense stands of bamboo. They depend on her for a milk supplement (during the weaning period) and for helping them to find the right bamboo.
Although the young are vulnerable to predators there is nothing to indicate that this is a major mortality factor. The giant panda diseases like some parasitic infestations, such as roundworm, may weaken members of the older generation and kill them. However there has been no evidence of major outbreaks or serious levels of illness. All of these pressures pale into insignificance in the face of the biggest killer of giant pandas Man. Humans kill pandas for their skins, sometimes using traps set for musk deer. But even worse is the constant war of attrition waged against, panda habitat in the name of timber products and ever more crops. Loss of natural habitat produces a slow decline in panda numbers as well as regular sharp losses during mass bamboo die-backs, when pandas in areas disturbed by Man have few alternative food sources.