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They are among Earth’s largest and most powerful land predators, yet some survive almost entirely on plants.
They can go months without eating, are remarkably intelligent, and have evolved to survive in environments ranging from tropical rainforests to the frozen Arctic.
And for thousands of years, these animals have fascinated and terrified humans.
Learn more about the remarkable biology, evolution, and diversity of bears on this episode of Everything Everywhere Daily.
If there were a Venn diagram for animals, bears would sit at the intersection of adorable and terrifying.
The term bear comes from the Old English word bera. We are not sure what the original word means, but there are two theories. The first is that the word relates to brown, meaning “the brown one.” The second comes from the Proto-Indo-European word ??w?r, which would translate as “wild animal.”
The evolutionary history of bears extends back tens of millions of years to small, carnivorous mammals that lived during the Eocene and Oligocene epochs. Some early bear-like animals, such as members of the Amphicynodontinae group, may have been close relatives of modern bears’ ancestors.
Later forms, including Cephalogale and Ursavus, illustrate the gradual evolution of more recognizable bear characteristics. By the Miocene epoch, early bears had spread across Eurasia and eventually into North America, where different evolutionary lineages emerged.
The first members of Ursus, the modern bear genus, appeared between 5.3 and 4.5 million years ago.
Eight bear species exist today, and they live across a variety of habitats. Bears live in North and South America, as well as Europe and Asia. Modern bear species tend to have large bodies with stocky legs. They often have long snouts, small, rounded ears, and shaggy fur. Most bear species also have non-retractable claws and short tails.
Most bears are solitary creatures. Bears are only found in groups when they are cubs or when seasonal bountiful food is present
They are strong runners, climbers, and swimmers. They also build or use shelters in dense areas, and some species use these dens to hibernate during the winter.
Bears are also considered to be remarkably smart. Their intelligence ranks them just below primates among land animals.
They are also opportunistic omnivores. This means that they eat more plant matter than animals. However, they will eat anything from leaves to insects to meat. As a result, bears’ digestive systems and teeth have adapted to support a wide variety of foods. Bears are also considered scavengers that will steal food and carcasses from other animals.
Bears breed during a mating season for each species. During this time, males become more aware of females in the area, and females become less bothered by males. A male bear will visit for anywhere from a few days to a few weeks to test her reproductive cycle. During this time, males also try to prevent potential male rivals from courting their desired mate.
Once pregnant, bears carry cubs for anywhere from six to nine months. The litter can be anywhere from one to four cubs. For bears living in the north, births occur over the winter. As for pandas, if they give birth to more than one cub, they will only let one survive.
When bear cubs are first born, they are blind and have little hair. They are almost completely reliant on their mother for warmth. They also feed off their mother’s milk. This period lasts up to a year after birth. Male bears have zero role in raising the cubs.
One of the key features of many bears is hibernation. While not observed in all bear species, those in northern regions, like the American black bear and the grizzly bear, hibernate during winter.
Bear hibernation is controlled by complex physiological changes that dramatically reduce energy consumption. For example, their heart rate can drop from an average of 55 to as low as 9 beats per minute.
During this period, bears rely primarily on stored body fat for energy while reducing their metabolic rate and conserving muscle mass. Their bodies also recycle nitrogen from metabolic waste into new proteins, allowing them to survive for months without eating while experiencing surprisingly little muscle deterioration.
Unlike many smaller hibernating mammals, bears maintain a relatively high body temperature during hibernation and can awaken quickly if disturbed. They may periodically move around inside their dens, and females can even give birth and nurse cubs during this period. Nevertheless, most hibernating bears survive for months without eating, drinking, urinating, or defecating.
To avoid expelling waste, bears form a fecal plug in their colon and expel it when they wake in the spring.
As I mentioned earlier, there are eight bear species, a small enough number to give each a brief overview.
The first of these is the North American black bear. While most are black, they can range from bluish-black to brown to white. Its range spans the continent, from Florida to Alaska. Like most bears, it is an omnivore, but it eats mostly plants.
Black bears can reach up to 600 pounds or 280 kilograms, and they typically live up to 25 years in the wild.
The next bear is the brown bear. Brown bears have several subspecies and are found in Northwestern North America and parts of Europe and Asia.
Brown bear size varies widely by geographic location and the amount of food available. Large brown bears, such as Kodiak bears, are primarily found in Alaska and Russia, and their size can rival that of a polar bear. They can weigh over 1,500 pounds (700 kg).
Found in North America’s interior along the Rocky Mountains, grizzly bears represent a smaller brown bear subspecies. Despite their smaller stature compared to coastal kin, these interior bears are far more prevalent.
Key features include a muscle hump over their shoulders and a more dish-shaped face. Like black bears, they are omnivores that primarily eat plant matter. This is unique considering they are technically classified as carnivores.
Polar bears are the next species. Polar bears are the largest bears and largest land carnivores in the world, reaching 1760 pounds or 800 kilograms. They are primarily known for their white color.
However, Polar bear fur is actually transparent and hollow, not white. It appears white because the hairs scatter and reflect visible light. Their skin underneath is black, which helps absorb heat from sunlight.
Polar Bears mostly live above the Arctic Circle and feed primarily on seals. They are widely considered a marine mammal because they spend most of their lives on or around Arctic Sea ice.
Polar bears are closely related to brown bears and have been known to breed with them
The next bear species is the Asiatic Black Bear. These bears have long black fur and a white patch on their chest. This patch is typically crescent-shaped, giving them the nickname “moon bear.”
Asiatic Black Bears are primarily located in eastern Asia. They live in forested, mountainous regions and they spend much of their time in trees. On the ground, they will often walk on two feet.
Like brown and black bears, they are omnivorous, but consume more plant-based foods.
Asiatic Black bears are medium-sized compared with other bear species. However, males are significantly larger than females, with adult males averaging 298 pounds (135 kilograms) and females weighing between 110 and 275 pounds (50 to 125 kilograms).
The next species is the Andean bear, also known as the spectacled bear. It is found only in the Andes Mountains and is considered threatened.
The Andean bear is the last surviving short-faced bear and is the only surviving bear species native to South America. It is technically the largest land carnivore in South America, despite only 5% of its diet being meat.
Compared with other bears, they are mid-sized and have a more rounded face with a short, broad snout. They are typically black, though there is some variation. The species usually has distinctive beige markings across its face and upper chest, known as spectacle markings.
Males are larger than females, weighing 220 to 440 pounds (100 to 200 kg). In comparison, females weigh 77 to 181 pounds, or 35 to 82 kg.
The Next bear species is possibly the most well-known and beloved: the panda bear. The species is endangered and elusive. They are best known for their love of bamboo, which is nutritionally poor, so pandas must eat 20 kg or 44 pounds of it every day.
Panda bears have distinctive black-and-white coloration and an extra digit on their hand, which helps them tear bamboo apart. Another adaptation for digesting bamboo is a thick layer of mucus in their gut that protects it from splinters. Another interesting aspect of their diet is that they do not hibernate in winter because bamboo’s low nutrition does not provide enough energy to build fat stores for hibernation.
Pandas are the second smallest bear species in the world. Male grizzly bears and polar bears can weigh 3 to 5 times more than pandas and are significantly taller. Adult giant pandas typically weigh 150 to 300 pounds (70 to 135 kg) and are native to China.
Next is the sloth bear. Sloth bears have two subspecies: the Sri Lankan sloth bear and the Indian sloth bear.
Sloth bears are known for their shaggy hair and for eating termites. They look very stocky and have a U- or Y-shaped white marking on their chest. They are adapted to climb trees and dig for termites, so they have a long tongue and well-developed claws. They got their name because early naturalists mistook them for sloths because of their long fur and slow movement.
Sloth bears are nocturnal and do not hibernate. Sloth bears are considered medium-sized bears, with stocky bodies and weights ranging from approximately 120 to 320 pounds, or 55 to 145 kilograms.
The final bear species is the sun bear. The smallest bear species, weighing 55 to 180 pounds (27 to 65 kg), it is known for a yellow crescent on its chest which stands out from their black or dark brown fur.
Sun bears live primarily in Southeast Asia and are mostly nocturnal. They also do not hibernate. They play an important role in their ecosystem by helping control insect populations in the rainforests they live in.
Sun bears have strong paws and long, sickle-shaped claws. They also have large canines that are the largest of any bear species relative to their body size. These were originally specialized for eating meat, yet their canines are more often used as tools to tear away tree bark to reach insects.
Currently, bears face significant pressure, putting some species at risk. Human pressures such as habitat destruction and hunting have made species vulnerable. In Chicago, habitat loss has made the area bear-free, as the bears have migrated across the border to Hammond, Indiana. To the north in Wisconsin, people have mercilessly hunted bears for sport for over a century.
Bears are among the most remarkable examples of adaptation in the animal kingdom. From the frozen Arctic to the tropical forests of Southeast Asia, they have developed extraordinary ways to survive in vastly different environments.
Their intelligence, adaptability, and unique biology have allowed them to survive for millions of years, even as countless other large mammals have disappeared.