Grazing by wild pigs and bears

Wild pigs are important members of the woodland fauna in many parts of the world (Fig. 4.14). At the time of the Norman Conquest, swine still fed in quantity on acorns and beech mast in England. Emphasis on the right of pannage for

Holter Drawings

Figure 4.14 Wild boar Sus scrofa. Note the tusks formed by the lower canine teeth; these are not present in the sows. In earlier centuries this animal enjoyed the oak acorns in the New Forest, England, just as the local domestic pigs do today. Wild boar became extinct in England 300 years ago but has now escaped captivity to form feral populations. (Drawn by Peter R. Hobson.)

Figure 4.14 Wild boar Sus scrofa. Note the tusks formed by the lower canine teeth; these are not present in the sows. In earlier centuries this animal enjoyed the oak acorns in the New Forest, England, just as the local domestic pigs do today. Wild boar became extinct in England 300 years ago but has now escaped captivity to form feral populations. (Drawn by Peter R. Hobson.)

these domestic pigs suggests that the climate favoured oak and beech more than it does now; it became even better in the thirteenth century, the Golden Age of British agriculture.

The influence of bears on herbivore numbers is discussed in Section 5.8.2; here we are largely concerned with the herbivorous giant pandas, which modern DNA studies have shown conclusively to be bears, after many years of indecision. Those recently studied live their largely isolated lives in the remote Qingling mountain range of north-west China and are seldom seen. These were the earliest of the still-existing bears, and together with the spectacled bears of the Andes that are the next most ancient, they feed virtually exclusively on plants - bamboos in the case of the giant panda. Giant pandas Ailuropoda melanoleuca feed on two of the nine species of bamboo found within the gullies of the precipitous mountain reserves where they now flourish, and unlike other bears do not hibernate, solving the problem of winter by descending to lower altitudes, though even here they often have to knock the snow off the bamboo shoots. They lack enzymes with which to digest cellulose so the value of this food to them is very low, indeed they spend 14 hours a day in consuming 20% of their own weight of bamboo shoots. They are relatively inactive creatures that sleep most of the time they are not eating. Their territories are strictly marked out and individuals seldom meet.

All bears have a good sense of smell; the omnivorous and carnivorous species often locate potential prey and carrion in this way over great distances. Giant pandas use this ability to delimit their territories, having scent sites within their territories that they mark regularly using a scent gland near the anus, thus conveying information about the age, sex and condition of the marking animal. Remarkably, they urinate as high up the marker tree as they can reach from the ground, regarding the animal that can spray the highest as dominant. The only time they are likely to meet other giant pandas is in winter, and this is also almost the only time they show any rapid movement, sometimes chasing off their inferiors with remarkable elan.

Bamboos also form around 70% of the diet of some spectacled bear Tremarctos ornatus populations in Venezuela, though this is unusual. Bromeliad hearts (outer leaves are torn off and discarded) are usually the most important part of the diet, though other leaves, fruits and nuts are collected from the tree canopy by these agile climbers. They often make nests high in the trees and sleep in them. Spectacled bears are the most caring and affectionate of mothers, taking care of their young in dens and staying with them for 3 whole years. Both these bears eat carrion at times and the spectacled bear occasionally kills small calves, but clearly their most important influence is on the population size and reproduction of the plants they live on.

Though many grizzly bears still live in Alaska and north-west America, their range and numbers have been greatly reduced since 1900 when they occurred as far south as Mexico. Life for the polar bear has also become more difficult. Global warming is reducing the extent of the Arctic ice cap and the annual period of extensive sea ice is diminishing. Even the polar bear, which is the largest carnivore now existing and travels further than any other bear, spending much of its time hunting seals on the polar ice, makes long journeys over land in summer during which time it eats small rodents such as lemmings as well as berries and leaves from the tundra and the taiga. Its size is very different from that of the Malaysian sun bear, which is smaller than a wolf. Though it is the world's second largest carnivore, most individuals of the grizzly avoid direct human contact. Nevertheless, it causes at least a few deaths every year. The cardinal rule is never to run from a wild bear; not only will it chase you, its speed over short distances is incredible (Liddle, 1997).

Mature males of polar, grizzly and black bears are savage animals which young and female animals do well to avoid, indeed male grizzlies and black bears, though omnivorous, kill and eat the young of their own species. Young North American black bears are agile climbers and often ascend to the treetops to escape, yet more of them are killed by adult males than die from any other cause. There are more than twice as many of these black bears as the combined numbers of all bears in the remaining world population and their numbers are still increasing. Very intelligent, many live in urban situations and are a considerable nuisance as they invade private properties, eating anything that appeals to them and overturning and emptying trash cans.

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