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Bears of North America
Sun bears, brown bears, sloth bears, spectacled bears, American black bears, Asian black bears, panda bears, and polar bears - these are the world's eight species of bears. They are all part of a family scientifically called Ursidae. Only three of these species live in North America. Do you know which ones?
North America is home to 1) American Black Bears (Ursus americanus), 2) Brown Bears (Ursus arctos), and 3) Polar Bears (Ursus maritimus). Each bear species has its own scientific name, and in the case of brown bears, many of its isolated populations have regional names as well.
Each of the North American bear species are distinctively different from each other and are unique to their habitats. Within each species there are also differences such as size, color, and diet based on where they live and the abundance of quality nutritious foods; even the season can make a difference.
The evolution of bears as we know them today began about 30 million years ago. Those ancestors, known as Ursavus, were part of a family called Miacids that also included canines. Although scientifically debated, it is believed that bears evolved from a canine approximately 5.3 million years ago. The earliest known bear ancestor is Ursus minimus, a small bear that steadily grew in size and diversity as it spread across Asia and Europe over time. Further evolution of North American bears differs and more information is provided for each of these species below.
The American Black Bear (Ursus americanus)
The American black bear is the smallest and most widely distributed of the North American bears. There are approximately 600,000 black bears native to North America, and they live in most of the United States, all of Canada and in parts of Mexico.
Habitat: Black bears originally lived in a wide variety of habitats due to their large geographic distribution, but now they are typically found in largely forested areas and mountainous terrain. This is because they have had to learn to adapt to man as we expand into their home ranges. Black bears tend to be the most timid of the North American bears due to their smaller stature, but they are still a strong and bold opponent. Though known to attack when provoked, for the most part however, black bears generally give humans a wide berth.
Evolution: It is believed that black bears evolved directly from Ursus minimus. They first existed in Asia, and those black bears that migrated across the Bering Land Bridge about 500,000 years ago became known as the North American Black Bear.
Description: Black bears have a convex (straight) face when seen in profile. Its eyes are small and the ears are tall and well-rounded. They can see and hear much better than a human and they have an excellent sense of smell that can range up to 20 miles. Black bears do not have the prominent shoulder hump which characterizes the brown bear, and their rumps are higher than their shoulders. Black bears have 42 teeth: 12 incisors, 4 canines, 16 premolars and 10 molars. The canines are long and well pointed; the premolars are rudimentary or even missing; and the molars have flat crowns.
The black bear is plantigrade, meaning it walks on the soles of its feet. They are also able to walk standing upright like a human. There are five toes on each foot, each armed with a strong, curved, nonretractable claw. The black bears front claws are about 1 1/4 inches in length.
Lifespan: The average life span of a black bear in the wild is 18 years. The oldest known wild black bear was 39 years old and the oldest black bear in captivity was 44 years old.
Size: The size of a black bear varies greatly based on their geographic area, food source, age, sex, health, and season. Black bears weigh anywhere between 90 and 875 pounds. The 875 pound bear is the largest known black bear and it was discovered in Pennsylvania. Males are larger than females and tend to average 400 pounds, while a female's average weight is 175 pounds. Black bears stand 27 to 36 inches high at the shoulder, and are 4 to 5 1/2 feet in length. When standing up, they are about five to seven feet tall. Black bear males will continue to grow until they are 10 to 12 years old.
Fur: The black bear is also unique in that it comes in a wide range of colors. A typical black bear has long, lustrous jet-black hair over most of the body from its head down to its tiny tail. On its muzzle and around its eyes, the hair is light-colored. Their fur is soft and dense with long, thick guard hairs. About 25% of black bears have a splash of pure white on their chests.
This splash may vary from just a few hairs to an area about a foot across. This white patch comes from their Asian ancestors. Black bears also come in almost every shade of brown including cinnamon, rust, and bright blond. A population of black bear that live on certain islands in western Canada and in British Columbia, known as the Kermode bear, has white fur. Another population that lives in Alaska, called the Glacier bear, has black fur that is tinted blue.
Diet: Black bears are omnivores and eat grass, plants, fruits, nuts, insects, larvae, honey, fish, small mammals, and carrion. They will also occasionally kill young deer and moose calves. It is easy for black bears to become inappropriately conditioned to human and pet foods and when that happens, they will come back for more. This is problematic for the safety of people and for the bear. When human food and garbage is easily accessible, bears will abandon traditional food sources they need to eat to be well nourished, which can lead to health problems as a result of improper nutrition. Bears will also eat anything with a food odor which includes plastic and even glass which can damage their digestive track and ultimately result in death. If the same bear continues to return or gets aggressive about obtaining human foods or livestock it will be euthanized. People can prevent this from happening.
Social Tendency: Black bears tend to be solitary animals, except that mothers with cubs will stick together. Sometimes the bears will congregate together at large food sources, and when they do a hierarchy is established between the bears, with males being the most dominant. Otherwise, males just briefly coexist with females during mating season.
Mating: Male black bears become sexually mature between the age of three to four years old and females are sexually active between the ages of two through nine years old. Bears are polygamous meaning they typically have more than one mate. The peak mating season is from June to mid-July and females generally mate every other year, or longer if food is scarce. Interestingly, the fertilized eggs do not begin to become embryos until the fall and although gestation is 220 days, it only takes 70 days from embryo development until birth. If the mother does not gain sufficient weight to support the embryos, then she will abort. Pregnant bears will den during the winter and give birth while hibernating, usually in January and February. Anywhere from one to five cubs may be born, but most times it is two or three.
Cubs: Bear cubs born together are called a litter. Newborn cubs weigh approximately half to one pound, and they are born with very fine hairs but not fur. Bear cubs do not open their eyes until they are five to seven weeks old. Mom and cubs generally stay in their den until April; and the cubs will weigh between four to 10 pounds at that time. The mother will begin weaning her cubs at six to eight months old, but they will stay with their mother through their second winter until they are about 17 months old. During this time the cubs learn to survive from their mother and grow to a size where they can begin defending themselves against other bears and predators that seek out the small, young and sickly.
Hibernation: The length of time a black bear hibernates is dependent on weather and availability of food. It can range from three weeks to eight months; and it is possible for hibernating bears to wake up and come out of their den for a bit. During hibernation the bear's body temperature stays the same at 95 degrees Fahrenheit but its heart rate will drop from 40-50 beats per minute to just eight beats per minute and slows down metabolism. They do not lose their muscle tone, however, they do lose approximately 30% of their weight which is why they need to bulk up during the fall. Bears do not urinate, defecate or eat during hibernation. Pregnant females will give birth while hibernating.
Characteristics: American black bears are very intelligent and curious. They are clever problem solvers when it comes to getting in places where there is food, especially human food. 
Black bears can run about 25 miles per hour. They are excellent swimmers and they like to swim for fun as well as to fish. They are also strong climbers and will climb trees to feed, escape enemies, and hibernate in tree holes and root cavities. When a mother bear senses danger, she will often send her cubs up trees while she stands guard at the bottom. Black bears are the only North American bear that often climbs trees as an adult.
Communication: Black bears communicate by body posturing and they make various facial expressions and use of their mouths. They are also vocal and use sounds such as huffing, tongue-clicking, and grunting. Warning signs include pawing or slapping the ground, teeth-clicking and lip popping. Bears also mark their territories by scent, and will sometimes mark trees using their teeth and claws as a way of communicating with other bears.
North American Brown Bears (Ursus arctos)
The Brown Bear species is the most widely distributed bear across the globe. They can be found in many countries throughout Europe and Central Asia, China, Canada, and the United States. There are approximately 200,000 brown bears in the world; with Russia having the largest population at 120,000 bears. North America is home to about 55,000 brown bears; wherein Western Canada has roughly 25,000 bears, while the United States has about 30,000. Most of the U.S. brown bears live in Alaska with a small population of about 1,500 in the lower 48 states of Montana, Idaho, Wyoming, and Washington.
Evolution: Brown bears, and their ancestor the cave bear, are believed to have evolved from Ursus etruscus, (a direct descendant of Ursus minimus) that originally lived in Asia 500,000 years ago. The brown bear likely moved into Europe and North Africa 250,000 years ago, and on to Alaska 100,000 years ago. They continued their journey east into Canada and the great plains of the United States, but it wasn't until about 13,000 years ago that brown bears migrated south into Mexico.
Threatened and Endangered Species Status: Although brown bears in general are considered a species of least concern, the population that continues to live in the lower 48 states, regionally known as grizzly bears, were placed on the U.S. Fish and Wildlife Service's Threatened and Endangered Species list on July 28, 1975. This isolated population of brown bear is considered threatened because of their population decline and reduction of their habitat to less than 2% of their traditional range due to excessive hunting and loss of food sources as humans ever expanded west across the United States. In Mexico, the grizzly bear became extinct as recent as 1964.
Current Habitat: The North American Brown Bear's habitat generally consists of forests, meadows, mountains, valleys, and coastal regions. Male grizzlies have large areas they consider their home range whereas female bears tend to stay within smaller ranges.
Description: All brown bears have dished-in facial profiles, small rounded ears, and obvious shoulder muscle humps. Their tails are short and stubby; and each forefoot has five curved claws. 
The front claws are often three to five inches long, whereas claws on the bears' hind feet are considerably shorter. Each adult bear has 42 teeth including four prominent, curved canine teeth, 12 incisors, 16 premolars and 10 molars.
Life Span: Brown bears in the wild generally live for 20 to 25 years. The oldest known wild brown bear lived to the age of 39 and the second longest was 35 years old. The longest living brown bear in captivity lived to the age of 35 years old. 
Size: A Brown bear's size varies the most of all bears. Their size differences are largely due to the area in which they live and whether there is an abundant quality food source. Coastal brown bears that live in Alaska and off British Columbia enjoy large salmon runs and can become as large as polar bears, weighing in at as much as 1,600 pounds. On average, coastal males weigh between 800 and 1,200 pounds while females range between 500 and 800 pounds. A coastal brown bear standing on all four feet is approximately 4 ½ feet at the shoulder and may reach nine feet in length. Standing upright, some male brown bears tower over eight feet tall.
Grizzly bears are proportionately smaller than coastal brown bears as their diet is more plant based and varies depending on the season. Grizzly males are larger than females. They stand about three and a half feet at the shoulder, average six to seven feet in length, and can weigh 800 pounds or more.
Fur: 
Brown bears come in a variety of colors ranging from black, dark brown, to blond, which is why they are often mistaken for black bears. Their hair is long and thick with conspicuous silver-tipped guard hairs. Some unique common names reflect their unique grizzled fur, such as the silver-tip, or golden bear due to a glossy gold streak that appears almost metallic in bright sunlight.
Diet: Brown Bears are omnivores. Although they are a formidable apex predator with no enemies except humans, they are opportunistic eaters and prefer not to put a lot of energy into catching prey. If they do go after an ungulate (hooved animal) they will take down the weak or young.
A coastal brown bear's diet consists of a lot of salmon; whereas a grizzly bear's diet is comprised of about 75% of plant foods. In certain areas in and around Yellowstone Park where there is an abundance of bison and elk, their diet is meatier.
Moths, whitebark pine nuts, ungulates, and salmon or trout are the best nutritional foods for a brown bear. However, depending on the season and food availability, brown bears also eat wolves and winter-killed animals such as elk, bison, and moose in the Spring; and grasses, a variety of plants and roots, leaves, berries, nuts, rodents, insects, ants, moths, fish, and carrion throughout the rest of the year. A brown bear's long, curved claws and powerful shoulders are well-suited for digging up these food sources.
In the fall, brown bears go through a phase called hyperphagia where they eat massive amounts of food to bulk up in order to have enough fat reserves to hibernate for the winter. They may gain as much as three pounds a day. Unfortunately, the bears will also eat human food and garbage when it is inappropriately available. Eating human foods can lead to nutritional and health problems, as well as a safety problem for people and the bears.
Social Tendency: Brown bears tend to be solitary animals but not territorial. When there is an abundant food source, like salmon in Alaska, coastal brown bears do not mind tolerating other bears. However, they do establish a pecking order, or hierarchy, where the strongest bears get first choice of fishing and relaxation areas. 
This hierarchy generally begins with male bears, then females with cubs, then single adult bears, and extends all the way down to the weakest and youngest bears who sometimes must wait for their turn to fish or get the poorest areas to feed and reside. Occasionally a male bear will give up his feeding spot to a mother bear with cubs in order to avoid a conflict that could result in injury.
Mating: Brown bears begin to breed when the females become 4 or 5 years old. 
Bears are polygamous meaning they typically have more than one mate, and their cubs can be from different fathers. The peak mating season is from May to mid-July and female brown bears generally mate once every three years. Although a brown bear's entire gestation period can be up to 270 days, the fertilized eggs do not begin to become embryos until the fall and it only takes 6 to 8 weeks from embryo development until birth. Not all impregnated females will develop embryos if food was too scarce and their bodies did not obtain sufficient fat to sustain them. Pregnant bears will den during the winter and give birth while hibernating, usually in January and February. Anywhere from one to four cubs may be born but most often there are two or three cubs in a litter.
Cubs: Newborn cubs weigh approximately 1 to 1 ½ pounds, and are born with very fine hairs but not fur. Bear cubs do not open their eyes until they are five to seven weeks old. Mom and cubs generally stay in their den until about April before emerging; and often stay nearby their den for some time afterward. The mother will begin weaning her cubs at the age of five months, but they will stay with her until they are 2 to 3 years old. Mother brown bears are fiercely protective of their cubs. Females are fully grown by 9 years old and males by 14 years. 
Denning: It is common for a grizzly bear to choose a den site that is hidden by dense vegetation and often at the base of a large tree or on a north-facing slope. The dens usually have a small doorway just large enough for the bear to squeeze through, then a small hallway or tunnel to its sleeping chamber. The bear will line the chamber with pine tree branches or other available material which helps retain the bear's body heat and keep it warmer. The dens can take up to a week to make and often require a lot of dirt to be moved by the bear. The small entrance and chamber cavity also help to keep the den warmer. Depending on the winter conditions, sometimes the entrance will get covered over with snow.
Hibernation: Brown bears will hibernate during the winter months in most parts of the world. The length of hibernation depends on a few factors: whether it is a pregnant female that births her cubs during hibernation; as well as how cold the winters are and whether or not food sources are plentiful. This hibernation period can be as long as 6 months or as little as a few weeks. Shorter hibernation periods are a result of warmer temperatures and ocean currents that bring warmer weather.
The body temperature of a hibernating brown bear drops slightly from its normal temperature range of 98.6 to 100.4 degrees to approximately 91.4 degrees. Its heart rate will go from approximately 45 beats per minute down to about 10-20 beats per minute; while the bear's breathing reduces significantly from 6-10 breaths per minute to just one breath in 45 seconds.
Unique Characteristics: Brown bears are very intelligent. They have excellent memories and are able to return to food sources they were shown as cubs. A brown bear's eyesight is very similar to a human's, and Native Americans say they have hearing that is acute enough to hear a pine needle fall from a tree. Their sense of smell is very strong and they are able to detect food many miles away. Brown bears are able to run at speeds greater than 30 miles an hour both up and down hill. They can cover 60 feet in as little as 1.6 seconds. They are also very good swimmers. Brown bears can climb trees though it is very rare for adult bears to do so because of their size and the shape of claws. Bear cubs, however, are known to be good climbers, especially in times of danger.
Polar Bear (Ursus maritimus)
Polar bears live in the Arctic and areas that surround the Arctic such as Canada, Russia, Greenland, Norway, and the United States. They are the largest of all eight bear species as well as the largest land-based predator in the world. Polar bears are also the only bear species that are marine mammals. It is estimated that there are between 22,000 and 31,000 polar bears in the world today. This makes them classified as a vulnerable species.
Habitat: The Polar Bear is the true King of the North, reigning as undisputed ruler of the frigid waters and frozen wastelands at the top of the world. Because of the vastness of sea ice, a polar bear's home range tends to be much larger than that of other bears. Not only do they have to compensate for a home that is constantly changing and moving, they must go where the seals are. The strength of the sea ice also affects how far a polar bear must travel.
Evolution: Polar bears evolved from brown bears about 150,000 years ago. They are a very specialized species, meaning their evolution was to adapt to their habitat of Arctic sea ice and seals as a primary source of food. Because of this specialization, it is unknown whether polar bears will be able to adapt over time to the lessening of sea ice and warmer climates.
Description: Polar bears are huge, long-necked, pear-shaped animals with sloping heads that appear small. Their ears are short and situated below the crown of the skull. Polar bears have a total of 42 teeth including four long canines, 12 incisors, 16 premolars and 10 molars. Their eyes, nose, lips, and claws are black. Polar bears can hear as well as humans and have good long-distance vision. It is their sense of smell that is exceptional. They can smell a seal up to one mile away or one that is buried under three feet of snow.
Polar bears are long-legged plantigrades, meaning they walk on the entire soles of their feet. There are five toes on each foot and claws are relatively short but thick and curved to help them hold on to prey, dig, and to run and climb on ice. Polar bear feet average 12 inches wide which helps distribute their weight when walking in snow or on thin ice and are also webbed to help them swim better. The pads of their feet are covered with small soft bumps and short insulating hairs that provide traction as the bears walk or run across the ice. Polar bears walk with a distinctive shuffling gait and are surprisingly quick and agile for such large animals.
Life Span: While it is rare for polar bears to live beyond 25 years, the oldest known wild polar bear died at age 32.
Size: Adult male polar bears stand about 4 to 5 feet tall at the shoulder with their length between 8 to 10 feet, and weigh between 800 to 1,600 pounds. Adult females are smaller than males, weighing in at 330 to 550 pounds and measuring 6 to 8 feet in length. However, a pregnant female can weigh as much as 1,100 pounds. The largest polar bear on record weighed in at 2,209 pounds in 1960.
Fur: Although polar bear fur appears white, it is actually translucent. Generally, the fur yellows with age. Polar bear hair is hollow and oily so that they can easily shake water and ice off after swimming. Under their fur, the skin is black so they can absorb the sun's heat. A polar bear has a layer of fat up to four inches thick beneath the skin that serves both as insulation and an energy source, especially when food is scarce. Males have long hairs on their forelegs which increase in length until they are 14 years old. It is thought that this foreleg hair is meant to attract females. Polar bears will overheat at temperatures above 50 degrees Fahrenheit; and shed their hair during the warmer months of May through August. Then their new winter coat will start growing in.
Diet: Polar bears are the largest land carnivores currently in existence. They are hypocarnivores meaning that their diet is mostly meat. In fact, polar bear food consists of 90% meat, most of which are seals but will also include rodents, muskox, reindeer, birds, other polar bears, and carcasses of whales and walruses. The remaining 10% is made up of seaweed, berries, roots, and bird eggs, however none of these are a good source of fatty nutrition and are usually consumed when the bears are not able to find or catch meat. Mature polar bears tend to eat only the calorie-rich skin and blubber of the seal, while younger bears consume the protein-rich red meat. Polar bears are very stealthy hunters both on ice and in the water. They usually hunt seals from where the edge of sea ice meets water, catching them as they come up to breath. They will also sneak up on seals while they are resting on the ice, or raid a mother's birthing den. After feeding, polar bears wash themselves with water or snow.
Social Tendency: Although polar bears are mostly solitary animals, they are not territorial. Adults have even been known to play together and sleep in an embrace. Cubs are especially playful and like other bears they will play fight to prepare for mating competitions when they are older. In areas like Churchill, Manitoba, polar bears gather to wait for the ice to be blown in and hardened to take them back out into the Hudson Bay.
Mating: Female polar bears become sexually mature at the age of four years in most areas. Males usually reach sexual maturity at six years; however, because competition for females is fierce, many do not breed until the age of eight or 10. Mating takes place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas. A male may follow the tracks of a breeding female for 60 or more miles, and once he finds her he often has to fiercely fight with other males to breed with her. Polar bears are usually polygynous, meaning that they will have more than one mate and it is possible for cubs to be born from different fathers. Because polar bears evolved from brown bears, they are able to mate with brown bears and produce fertile offspring.
The gestation period is between 195 to 265 days. After mating, the fertilized egg remains in a suspended state until August or September. During this time, the pregnant female eats large amounts of food to gain enough weight to sustain her and the cubs while in their den.
Cubs: Cubs are born between November and February. Like other bear cubs they are born with their eyes closed, however, polar bear cubs are born with light down fur for warmth. Cubs weigh less than 2 pounds at birth and generally a litter consists of two cubs. 
They will remain in the den until mid-February to mid-April. When the mother breaks open the den to come out the cubs will weigh between 22 and 33 pounds. Mother and cubs will stay near their den for about 12 to 15 days, before they begin the long walk to the sea ice. Depending on the timing of ice-flow breakup in the fall, she may have fasted for up to eight months. Mother bears generally wean their cubs at the age of 2 ½ years when she will either chase them away or abandon them. After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months.
Hibernation: With the exception of pregnant females, polar bears are active year-round and do not hibernate. During summer and fall months when there isn't ice to hunt seals from, polar bears often go without eating and live off their fat reserves. Pregnant females usually will make a den on land a good distance from the sea. They choose the sides of mountains or where there is a good slope. Dens are usually made in soft snow, but sometimes in the permafrost when there is not yet snow. Permafrost is a thick subsurface layer of soil that remains frozen throughout the year. In the den, the mother bear will enter a hibernation-like sleep but will also be awake at times. Her body temperature will remain the same at 98.6 degrees Fahrenheit, but her heart beat will drop from 46 beats per minute to 27 beats.
Characteristics: Polar bears can run at speeds over 25 miles per hour and swim tirelessly at speeds conservatively estimated at six miles per hour. Polar bears are able to jump eight feet out of the water to surprise a seal; and can swim underneath the ice and break their way back up. These white bears have been sighted at sea swimming strongly more than 100 miles from the nearest landfall. 
Communication: Mother bears are very loving and protective of their young. To communicate with the cubs she will make moans and chuffs. Chuffs are when the bear blows through the nostrils, producing a breathy snort. This sound is non-threatening and often used to reassure the cubs. When in distress cubs and subadults will squeal, bawl, bleat (a wavering cry), or scream. Nervous bears will make huffing sounds and snorts. While growls, hisses, and roars are an indication of aggression. Polar bear feet also leave a scent on the ground that allows them to keep track of each other.
Just like the evolution of the bear, there are a lot of opinions and conflicting statistical statements about bears in general, particularly concerning brown bears. There is a great amount of resources available, like Wikipedia, bear websites, books, and publications, and it is a good idea to refer to several sources when making your own conclusions.
