Friday, September 2, 2011

Asian Black Bear

The Asian black bear (Ursus thibetanus), also known as the moon bear or white-chested bear is a medium-sized species of bear, largely adapted for arboreal life, which occurs through much of southern AsiaKorea, northeastern China, the Russian far east andHonshū and Shikoku islands of Japan. It is classed by the IUCN as a vulnerable species, mostly due to deforestation and active hunting for its body parts. The species is morphologically very similar to some prehistoric bears, and is thought by some scientists to be the ancestor of other extant bear species.Though largely herbivorous, Asian black bears can be very aggressive toward humans, and have frequently attacked people without provocation. The species was described by Rudyard Kipling as "the most bizarre of the ursine species.".Asian black bears are close relatives to American black bears, with which they share a European common ancestor which is thought to have diverged 3 million years ago, though genetic evidence is inconclusive. Both American and Asiatic species are considered sister taxa, and are more closely related to each other than other species of bear. The earliest American black bear fossils, which were located in Port KennedyPennsylvania, greatly resemble the Asiatic species The first mt DNA study undertaken on Asian black bears suggested that the species arose after the American black bears, while a second study could not statistically resolve the branching order of sloth bears and the two black species, suggesting that these three species underwent a rapid radiation event. A third study suggested that American black bears and Asian black bears diverged as sister taxa after the sloth bear lineage and before the sun bear lineage. Further investigations on the entire mitochondrial cytochrome b sequence indicate that the divergence of continental and Japanese black bear populations might have occurred when bears crossed the land bridge between the Korean peninsula and Japan 500,000 years ago, which is consistent with pale ontological evidence.
Asian black bears are similar in general appearance to brown bears, but are more lightly built and more slender limbed.The skulls of Asian black bears are relatively small, but massive, particularly in the lower jaw. Adult males have skulls measuring 311.7–328 mm (12.3–13 in) in length and 199.5–228 mm (7.9–9 in) wide, while females have skulls measuring 291.6–315 mm (11.5-12.4 in) long and 163–173 mm (6.4-6.8 in) wide. Compared to other bears of the genus Ursus, the Black bears typically inhabit deciduous forests, deserts, mixed forests and thornbrush forests. They rarely live in elevations of more than 12,000 feet (3,700 m). They usually inhabit elevations of 11,480 feet (3,500 m) in the Himalayas in the summer, and will climb down to elevations of 4,920 feet (1,500 m) in winter. They sometimes occur at sea level in Japan.
The fossil record indicates that black bears once ranged as far west as Germany and France, though the species now occurs very patchily throughout its former range, which is now limited to the Asian continent. Black bears occupy a narrow band from southeastern Iran eastward through Afghanistan and Pakistan, across the foothills of the Himalayas in India, toMyanmar. With the exception of Malaysia, black bears occur in all countries in mainland Southeast Asia. They are absent from much of east-central China, though they have a patchy distribution in the southern and northeastern part of the country. Other population clusters exist in the southern Russian Far East and into North Korea. South Korea has a small remnant population. Black bears also occur in Japan's southern islands of Honshu and Shikoku and on Taiwan and Hainan.
There is no definitive estimate as to the number of Asiatic black bears: Japan posed estimates of 8-14,000 bears living on Honshu, though the reliability of this is now doubted. Although their reliability is unclear, rangewide estimates of 5–6,000 bears have been presented by Russian biologists. Rough density estimates without corroborating methodology or data have been made in India and Pakistan, resulting in the estimates of 7–9,000 in India and 1,000 in Pakistan. Unsubstantiated estimates from China give varying estimates between 15–46,000, with a government estimate of 28,000projections of the skull are weakly developed; the sagittal crest is low and short, even in old specimens, and does not exceed more than 19–20% of the total length of the skull, unlike in brown bears, which have sagittal crests comprising up to 41% of the skull's length. Although mostly herbivorous, the jaw structure of Asian black bears is not as specialised for plant eating as that of pandas: Asian black bears have much narrower zygomatic arches, and the weight ratio of the twopterygoid muscles is also much smaller in Asian black bears. However, the lateral slips of thetemporal muscles are thicker and stronger in black bearsWithin Sikhote-Alin, the breeding season of black bears occurs earlier than in brown bears, starting from mid June to mid August. Birth also occurs earlier, in mid January. By October, the uterine horns of pregnant females grow to 15–22 mm. By late December, the embryos weigh 75 grams.Sows generally have their first litter at the age of three years. Pregnant females generally make up 14% of populations. Similar to brown bears, Asian black bears have delayed implantation.Sows usually give birth in caves or hollow trees in winter or early spring after a gestation period of 200–240 days. Cubs weigh 13 ounces at birth, and will begin walking at four days of age, and open their eyes three days later. The skulls of newborn black bear cubs bear great resemblance to those of adult sun bears. Litters can consist of 1–4 cubs, with 2 being the average.Cubs have a slow growth rate, reaching only 2.5 kg by May.Black bear cubs will nurse for 104–130 weeks, and become independent at 24–36 months. There is usually a 2–3 year interval period before females produce subsequent litters.The average lifespan in the wild is 25 years, while the oldest Asian black bear in captivity died at the age of 44.

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