Ursidae is a small family - just eight species in five genera - that packs a big punch. It includes the biggest members of the order Carnivora and the biggest terrestrial mammals next to elephants and ungulates (hoofed mammals).
polar bear• Classification
• Homes
> Distribution
> Habitat
> Habitat Niche
• Morphology
> Appearance
> Anatomy
• Physiology
• Locomotion
• Diets
• Behavior
• Reproduction
• Ecology
• Evolution
• Relations with People
giant pandaUrsids include the northernmost mammal, the polar bear, and one of the most beloved animals, the giant panda. The brown bear is widely perceived as the strongest, fiercest animal in the boreal forest and northern tundra. It has long been a symbol of Russia, while the grizzly bear (a variety of brown bear) is a symbol of the American West and the ever shrinking wilderness. In contrast, the benign Teddy bear ranks as one of the most cherished children’s toys.
With their plantigrade feet, dexterous front feet (plus an opposable “thumb” in pandas), ability to stand erect and generally omnivorous diet, bears are among the species that most resemble humans. During the Ice Age, early humans may have even competed with the fabled cave bear for homes.
Northern-temperate bears, left to right: brown bear, American black bear, Asiatic black bear
Tropical bears, left to right: South American spectacled bear, Asian sloth bear and sun bearLove’em or hate’em, bears are intriguing. Without them, the world would be - well, unbearable.
Classification
Living carnivores (i.e. members of the mammal order Carnivora) are commonly divided into two groups, feliform (including the cat family, Felidae) and caniform (including wolves and dogs, Canidae). Bears are classified as caniform carnivores, along with raccoons (Procyonidae) and weasels (Mustelidae). (See a Feliform vs Caniform chart)
Names
Ursids are collectively called bears except for the giant panda, which is usually called a panda. Bears are sometimes casually referred to as bruins, derived from the name of the bear in Reynard the Fox.
Beyond that, bear names can get confusing. The grizzly bear and Kodiak bear are varieties of brown bear, and some American black bears can be just as brown as brown bears. There are also two black bears - the American black bear and Asian black bear.
The young of all ursids are called cubs. Older males are called boars, females sows.
Internal Classification
The polar bear, brown bear, American black bear and Asian black bear are placed in the same genus, Ursus. The panda and the three tropical ursids are each placed in its own genus.
The giant panda’s classification has long ranked as one of zoology’s greatest puzzles. Various authorities have classified it with bears in family Ursidae, with raccoons (Procyonidae) or with the red or lesser panda (Ailuridae). Molecular analyses have confirmed what most of us always knew: The giant panda is a bear.
What most people don’t know is that the polar bear and brown bear are virtually kissing cousins. The polar bear evolved fairly recently, roughly 150,000 years ago, likely sprouting from a population of brown bears that was isolated by glaciers during the Pleistocene (“Ice Age”).
In fact, some brown bear populations are believed to be more closely related to the polar bear than to other brown bears. Brown and polar bears can interbreed and even produce fertile hybrid offspring. However, such offspring would probably be doomed in the wild, as neither species can survive in the other’s niche.
The last surviving member of a lineage known as short-faced bears, the spectacled bear is sometimes placed in the subfamily Tremarctinae.
Homes
Distribution
Bears are native to all continents except Australia and Antarctica. However, bears are represented in South America by just one species that occurs primarily in the Andes, the spectacled bear. Similarly, the only bear that lived in Africa was the brown bear, which was found in Morocco’s Atlas Mountains. Unfortunately, Africa’s brown bears were exterminated, along with the Atlas lion.
| Distribution | OW | NW |
|---|---|---|
| polar bear | X | X |
| brown bear | X | X |
| American black bear | X | |
| Asian black bear | X | |
| giant panda | X | |
| sloth bear | X | |
| sun bear | X | |
| spectacled bear | X |
The polar bear is the most northerly mammal, roaming the frozen Arctic Ocean, while the spectacled bear is the only bear that lives south of the Equator. The brown bear is the most widespread species, formerly ranging across the tundra, forests and grasslands of Eurasia and North America.
The table below lists the continents and ecozones that each ursid is native to.
| Species | Continent | Ecozone |
|---|---|---|
| polar bear, brown bear | Eurasia, North America | holarctic (Palearctic + Nearctic) |
| American black bear | North America | Nearctic |
| giant panda | Eurasia (Asia only) | Palearctic |
| Asian black bear | Eurasia (Asia only) | Palearctic, Indo-Malayan |
| sloth bear, sun bear | Eurasia (Asia only) | Indo-Malayan |
| spectacled bear* | North America, South America | Neotropic |
| *The spectacled bear ranges into southern Central America (Panama), which GeoZoo regards as a southern extension of North America. | ||
Habitat
Bears occur in a wide variety of habitats. The polar bear is sometimes classified as a marine mammal, while other species inhabit forests in tropical America (spectacled bear) and tropical Asia (sloth bear, sun bear).
The wide-ranging brown bear is at home in more varied habitats than any other species, while China’s giant panda is the most selective species, limited largely by its staple food, bamboo.
Habitat Niche
All bears are primarily ground dwellers, though most can climb trees, as cubs at least. The most arboreal species is the spectacled bear, while the polar bear is the most aquatic ursid.
Morphology
Appearance
If bears could be described with just one word, that word might be robust. Of course, most bears are big, but they’re noticeably stocky even for their size. With their binocular vision, ability to stand erect and short tails, they look something like a cross between a gorilla and a dog. (In fact, the Malayan sun bear is nicknamed the “dog bear.”) Their plantigrade feet and enormous claws also recall extinct giant ground sloths, which could similarly stand on two legs.
Ironically, one of the few living animals living in bear country that could be mistaken for a bear is a rodent. I think I recall reading that pioneering arctic field biologist once briefly mistook a porcupine for a grizzly bear, something that I once experienced myself. And if that sounds stupid, I’ll point out that porcupines have plantigrade feet, similar to bears and humans.
Marsupials that resemble bears include the koala “bear” and wombats. (It isn’t hard to guess what inspired the common wombat’s scientific name, Vombatus ursinus.)
But enough comparisons. Let’s take a closer look at bears on their own terms.
Color
The names polar bear, brown bear and black bear say it all - or do they?
| Bear Colors | |
|---|---|
| polar bear | white |
| brown bear | brown (variable) |
| American black bear | black, with color phases ranging to white; occasional white marks on chest |
| Asian black, sloth and sun bears | black with prominent light chest markings |
| spectacled bear | black with prominent beige facial markings |
| giant panda | black and white |
Brown bears vary in color, some appearing almost blonde. There is even more variation among black bears.
The cinnamon bear (Ursus americans cinnamomomum) is a subspecies with brown or reddish-brown fur. Even more striking is the Kermode bear (Ursus americanus kemodei) of northwestern Canada, which often has creamy white fur, inspiring the nicknames glacier bear and spirit bear. Yet another variety with a beautiful bluish coat is known as the glacier bear.
Some American black bears have white or light brown chest markings. Most cubs are born with these chest blazes, though many lose them as they age.
Asian black bears, sloth bears, spectacled bears and sun bears are primarily black. However, the spectacled bear typically has prominent beige facial markings, while the other species have prominent markings on their chests. The Asian black bear is nicknamed the moon bear for what appears to be a white crescent moon on its chest, though it can also resemble a giant letter V.
The sun bear derives its name from a bib-shaped golden or white shape that represents the rising sun, according to legend.
The giant panda is famous for its bold black-and-white color pattern, reminiscent of an orca.
Size
There’s no question that bears are big, though which species is biggest is a matter of dispute. If we compare species based on average size, the polar bear is the clear winner, growing to weights of more than 1,500 pounds. However, one brown bear subspecies, the Kodiak bear (Ursus arctos middendorffi) is often cited as the biggest bear. In contrast, brown bears living on the northern tundra may be just one third the size of polar and Kodiak bears.
| Relative Size | lb. | kg |
|---|---|---|
| polar bear | 880-1,760 | 400-800 |
| brown bear | 660-1,760 | 300-800 |
| American black bear | 100-900 | 47-409 |
| spectacled bear | 220-440 | 100-200 |
| giant panda | 220-350 | 100-160 |
| Asian black bear | 242-330 | 110-150 |
| sloth bear | 176-308 | 80-140 |
| sun bear | 55-143 | 25-65 |
If we include prehistoric bears, the biggest known species was a giant South American short-faced bear (Arctotherium angustidens) that may have weighed as much as 3,500 pounds. (Read about it here).
The sun bear is undisputably the smallest bear, weighing as little as fifty-five pounds.
The other bears overlap in size. Note, also, that male ursids are significantly bigger than females.
Anatomy
Teeth
Bears’ long slightly hooked canines are a reminder that bears have a carnivorous heritage, while their flat, heavy molars are suited to crushing the plant matter most species eat. Insicors are not specialized and the first three premolars are reduced or lost. The carnassial teeth are relatively undeveloped compared to other members of the Carnivora except for the polar bear, whose carnivorous diet has apparently triggered the re-evolution of fully functional carnassials.
(What’s a The dental forumla varies considerably even within a given species, perhaps a sign that bears are still evolving towards a predominantly herbivorous diet. The dental formula on the right is typical of all ursids except the sloth bear, which only has two upper incisors for a total of 40 teeth.
Feet
While most carnivorans are digitigrade (picture the paw of a dog or cat), bears are plantigrade, walking “flat-footed,” similar to humans. (The bones of a bear’s rear foot are pictured on the left.)
Tails
Bears have extremely short tails. The longest ursid tail, measuring as much as seven inches long, is carried by the sloth bear.
Physiology
Senses
Bears have poorly developed senses of sight and hearing. However, at least some species have a powerful sense of smell, as many people who have stored food in tents have discovered.
Hibernation
The brown bear and American and Asian black bears feast heavily, gaining weight before entering a den for a period of deep sleep during winter. But anyone discovering an occupied den should keep their distance, for hibernating bears awaken easily.
In fact, bears are not true hibernators, lacking the physiological characteristics exhibited by animals that truly hibernate (e.g. lower heart rate, breathing rate, body temperature and blood pressure).
Nevertheless, the word hibernation is commonly applied to bears’ deep slumber, which is pretty remarkable. Imagine sleeping for several months without eating, drinking or passing waste!
Bear hibernation - or non-hibernation - is closely tied to temperature (and probably ultimately to food availability). In fact, American and Asian black bears don’t hibernate in the southern, warmer portions of their range - except for pregnant females. With a relatively constant food supply, polar bears don’t hibernate , either, with pregnant females - who excavate dens out of snow - again the exception.
The tropical sloth, sun and spectacled bears apparently don’t hibernate at all due to their warm environment and relatively stable food supply. Ever the anomaly, the giant panda can’t hibernate because its bamboo diet doesn’t allow it to store enough fat.
Life Span
Bears have a natural life span of about 15-30 years, though they may live longer in captivity.
Diet
Bears are among the most omnivorous members of the order Carnivora. The most carnivorous ursids are the polar bear and India’s sloth bear, which preys primarily on termites. At the other extreme, the giant panda is an herbivore, feeding almost exclusively on bamboo. The spectacled bear is also primarily herbivorous.
However, most bears eat whatever’s available. For example, brown bears may prey heavily on caribou and moose calves and congregate along rivers when salmon are spawning. But when the deer and salmon are gone, they feed on lush grasses, berries and carrion.
Some bears use their long, sturdy claws to dig for food, including rodents and insect larvae. Many bears are also fond of honey; in fact, the sun bear is nicknamed the “honey bear.”
Behavior
Adult bears are typically solitary except during the mating season. Male polar bears sometimes aggregate, and brown bears often gather to fish for salmon, though they fiercely defend choice fishing spots.
Most ursids are primarily diurnal. However, the three tropical species - sloth bear, sun bear and spectacled bear - are primarily nocturnal.
| sq mi | sq km | |
|---|---|---|
| grizzly bear | 300-700 | |
| American black bear | 15-77 | 40-200 |
Bears occupy enormous home ranges, the size varying with food supply, which in turn varies with the seasons. A polar bear may patrol a domain of more than 48,000 square miles (125,000 square km).
cave bears (Ursus spelaeus)
Bears and People
Wow, where does one begin? Bears figure in mythology, religion, folklore and politics, from the Russian bear to the Big Dipper (Ursa Major). But let's get the ugly stuff out of the way, first.
Man-Eaters
Yes, some bears have been known to eat people - particularly the polar bear, brown bear and American and Asian black bears. And for every person that's eaten by a bear, there are probably a couple dozen who are simply killed or badly mauled.
If that sounds scary, take a closer look at the statistics. Bear attacks are actually amazingly rare, especially considering the millions of people who work and play in bear country. Equally amazing is the number of people who survive bear attacks.
A Wikipedia fan compiled a List of Fatal Bear Attacks in North America. It looks gruesome, but the records go back more than a century.
The Sloth Bear of Mysore killed at least a dozen people and injured a couple dozen others before it was tracked down and shot. The Sankebetsu brown bear incident was the worst bear attack in Japanese history, resulting in the deaths of several settlers over a six-day period in 1915.
(To be continued; under constrution)
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