THE NORTH AMERICAN BLACK BEAR
The American black bear is a medium-sized bear native to North America. It is the continent's smallest and most widely distributed bear species. Black bears are omnivores with their diets varying greatly depending on season and location. They typically live in largely forested areas, but do leave forests in search of food. Sometimes they become attracted to human communities because of the immediate availability of food. The American black bear is the world's most common bear species.Despite living in North America, American black bears are not closely related to brown bears and polar bears; genetic studies reveal that they split from a common ancestor 5.05 million years ago. Both American and Asian black bears are considered sister taxa, and are more closely related to each other than to other species of bear. Reportedly, the sun bear is also a relatively recent split from this lineage.
Evolution
Despite living in North America, American black bears are not closely related to brown bears and polar bears; genetic studies reveal that they split from a common ancestor 5.05 million years ago. Both American and Asian black bears are considered sister taxa, and are more closely related to each other than to other species of bear. Reportedly, the sun bear is also a relatively recent split from this lineage.
The ancestors of American black bears and Asiatic black bears diverged from sun bears. The American black bear then split from the Asian black bear. The earliest American black bear fossils, which were located in Port Kennedy, Pennsylvania, greatly resemble the Asiatic species, though later specimens grew to sizes comparable to grizzlies. From the Holocene to present, American black bears seem to have shrunk in size, but this has been disputed because of problems with dating these fossil specimens.The American black bear lived during the same period as short-faced bears and the Florida spectacled bear. These Tremarctine bears evolved from bears that had emigrated from Asia to North America. The short-faced bears are thought to have been heavily carnivorous and the Florida spectacled bear more herbivorous, while the American black bears remained arboreal omnivores, like their Asian ancestors. The black bear's generalist behavior allowed it to exploit a wider variety of foods and has been given as a reason why, of these three genera, it alone survived climate and vegetative changes through the last ice age while the other more specialized North American predators went extinct. However, both Arctodus and Tremarctos had survived several other ice ages. After these prehistoric Ursids went extinct during the last glacial period 10,000 years ago, black bears were probably the only bear present in much of North America until the arrival of brown bears to the rest of the continent.
The ancestors of American black bears and Asiatic black bears diverged from sun bears. The American black bear then split from the Asian black bear. The earliest American black bear fossils, which were located in Port Kennedy, Pennsylvania, greatly resemble the Asiatic species, though later specimens grew to sizes comparable to grizzlies. From the Holocene to present, American black bears seem to have shrunk in size, but this has been disputed because of problems with dating these fossil specimens.The American black bear lived during the same period as short-faced bears and the Florida spectacled bear. These Tremarctine bears evolved from bears that had emigrated from Asia to North America. The short-faced bears are thought to have been heavily carnivorous and the Florida spectacled bear more herbivorous, while the American black bears remained arboreal omnivores, like their Asian ancestors. The black bear's generalist behavior allowed it to exploit a wider variety of foods and has been given as a reason why, of these three genera, it alone survived climate and vegetative changes through the last ice age while the other more specialized North American predators went extinct. However, both Arctodus and Tremarctos had survived several other ice ages. After these prehistoric Ursids went extinct during the last glacial period 10,000 years ago, black bears were probably the only bear present in much of North America until the arrival of brown bears to the rest of the continent.
Habitat
Throughout their range, habitats preferred by American black bears have a few shared characteristics. They are often found in areas with relatively inaccessible terrain, thick understory vegetation and large quantities of edible material. The adaptation to woodlands and thick vegetation in this species may have originally been due to the black bear having evolved alongside larger, more aggressive bear species, such as the extinct short-faced bear and the still living grizzly bear, that monopolized more open habitats and the historic presence of larger predators such as smilodon and the American lion that could have preyed on black bears. Although found in the largest numbers in wild, undisturbed areas and rural regions, black bears can adapt to surviving in some numbers in peri-urban regions as long as they contain easily accessible foods and some vegetative coverage. In most of the contiguous United States, black bears today are usually found in heavily vegetated mountainous areas.The spruce-fir forest dominates much of the range of the black bear in the Rockies. Important nonforested areas here are wet meadows, riparian areas, avalanche chutes, roadsides, burns, sidehill parks, and subalpine ridgetops. In areas where human development is relatively low, such as stretches of Canada and Alaska, American black bears tend to be found more regularly in lowland regions. In parts of northeastern Canada, especially Labrador, black bears have adapted exclusively to semi-open areas which are more typical habitat in North America for brown bears.
Relationship with humans
Although an adult bear is quite capable of killing a human, American black bears typically avoid confronting humans when possible. Unlike grizzly bears, which became a subject of fearsome legend among the European settlers of North America, black bears were rarely considered overly dangerous, even though they lived in areas where the pioneers had settled. Black bears rarely attack when confronted by humans, and usually limit themselves to making mock charges, emitting blowing noises and swatting the ground with their forepaws.Compared to brown bear attacks, aggressive encounters with black bears rarely lead to serious injury. However, the majority of black bear attacks tend to be motivated by hunger rather than territoriality, and thus victims have a higher probability of surviving by fighting back rather than submitting. Unlike grizzlies, female black bears do not display the same level of protectiveness to their cubs, and seldom attack humans in their vicinity. However, occasionally, attacks by protective mothers do occur.In almost every case where open dumps or handouts that had previously attracted black bears were ceased, the amount of aggressive encounters with bears have decreased precipitously over time. However, in the aforementioned case of the spree attack in Liard River Hot Springs, the attacking bear was believed to have been previously almost fully dependent on a local garbage dump that had closed and was starving as a result of the loss of that food source. Attempts to relocate bears are typically unsuccessful, as black bears seem to be able to return to their home range even without familiar landscape cues.
Reproduction and Development
Sows usually produce their first litter at the age of 3–5 years. Sows living in more developed areas tend to get pregnant at younger ages.[61] The breeding period usually occurs in the June–July period, though it can extend to August in the species' northern range. The breeding period lasts for 2–3 months. Both sexes are promiscuous. Males try to mate with several females but large, dominant ones may violently claim a female if another mature male comes near.Sows tend to be short tempered with their mates after copulating. The fertilized eggs undergo delayed development and do not implant in the female’s womb until November. The gestation period lasts 235 days, and litters are usually born in late January to early February. Litter size is between one and six cubs; typically two or three. At birth, cubs weigh 280–450 g (0.62–0.99 lb), and measure 20.5 cm (8.1 in) in length. They are born with fine, gray, downlike hair, and their hind quarters are underdeveloped. They typically open their eyes after 28–40 days, and begin walking after 5 weeks. Cubs are dependent on their mother's milk for 30 weeks, and will reach independence at 16–18 months. At the age of six weeks, they attain 900 g (2.0 lb), by 8 weeks they reach 2.5 kg (5.5 lb) and by the age of 6 months they weigh 18 to 27 kg (40 to 60 lb). They reach sexual maturity at the age of three years, and attain their full growth at 5 years.
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