Bear Anatomy and Physiology (2023)

Anatomy and physiology of the bear

In this section we take a comprehensive look at the different subspecies, physiology and anatomy of bears.

And don't miss the VIDEO ofWayne Gast of Lethal Injection Outdoors on his successful black bear hunt in Saskatchewan.It is between Bear Size and Bear Wright. To enjoy. Robert Hoage

bear size

The male bear is relatively larger than the female in almost all bear species.

Bear Sizes: Male x Female

  • American black bears - males 33% larger
  • Brown Bears (Kodiak) - Males are 40% to 50% larger
  • Grizzly Bears - 38% larger males
  • Polar Bears - Males 25% to 45% larger
  • Asiatic black bears - slightly larger males
  • Giant pandas - males are 10% to 20% larger
  • Lazy Bears - Slightly larger males
  • Sun Bears - Males 10% to 15% 1 larger
  • Spectacled Bears - 33% larger males

Alaskan brown bears and polar bears are arguably the largest bears.

JUST A SECOND, let's get into the black bear hunting spirit and follow Wayne Gast as he hunts and succeeds on a Saskatchewan black bear. Click on the video below.

carry weight

Bear weight varies between species, with polar bears and Alaskan brown bears being more than 10 times heavier than sun bears. While these species differences are partly genetic, they are mostly the result of variations in habitat, particularly diet. For example, Alaskan brown bears from the coastal regions of North America with a large fish source and more lush vegetation weigh almost twice as much as inland brown bears (grizzly bears).

Causes of individual weight differences between bears of the same species and sometimes the same habitat can include individual health, age, sex of the bear, individual ability to find food or to digest certain foods, and ability to withstand impact in Habitat.

Seasonal fluctuations in the weight of individual bears are common. Fall (pre-sowing) weights tend to be much larger than spring (emergence) weights. Weight is influenced by seasonally available foods.

American black bears from eastern North America are consistently larger than those from western states. (Weights are average values ​​for a given sample.)

  • New York – men 273 pounds, women 196 pounds
  • California – males 216 pounds, females 127 pounds

Brown bears in Wyoming/Montana are larger than those in the Yukon Territory. (Again, weights are average values ​​for a given sample.)

  • Wyoming - males 539 pounds, females 334 pounds
  • Yukon Territory - males 315 pounds, females 209 pounds

Bear weights are obtained when bears are taken during a hunt, when they are killed illegally (poaching), and when they are withheld for handling and research. The following weights for some states and provinces are "dressed" weights from bears collected by hunters or caught during handling.

Weights of mature men

  • American Black Bear - average 250lbs, range 125-600lbs, heaviest recorded 803lbs
  • Brown Bear - average 725lbs, range 500-900lbs, heaviest recorded 2500+lbs
  • Grizzly Bear - average 490 pounds, range 350-700 pounds, heaviest recorded 1496 pounds
  • Polar Bear - Average 1,150 pounds, range 900-1,500 pounds, heaviest recorded 2,210 pounds

Bear Weights in Lore and Legend - Lore and Legend has provided some very impressive bear weights:

  • Kamchatkan (Commonwealth) Brown Bear – 2500 pounds
  • American Black Bear (in the 19th century) - 1,800 pounds
  • California brown bear (early 1900's) - 2350 lbs

"Legendary" weights are still not uncommon today. Ben East reports in Bears on a zoo director's comment on such weights: ". . . Few record-weight grizzly bears hail from a part of the country where accurate scales are found. And Adolph Murie, in A Naturalist In Alaska, states that "the length of a scale a bear always weighs more."

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bear height

A bear's height is measured from the bottom of its paw on the ground to the highest point of its shoulder. What follows are the average reaches, or heights, for adult males.

  • American Black Bear - 2.5-3 feet.
  • Brown Bear - 3-5 feet.
  • Polar Bear - Up to 5.3 feet.

In comparison, the size of an American bison is five feet; eight elephant feet; hippopotamus five feet; six foot rhino; and a three foot Siberian tiger.

bear length

A bear's length is measured from the tip of its nose to the tip of its tail. The average lengths (ranges) of adult males are listed below.

  • American Black Bear - 6 feet.
  • Brown Bear - 7-10 feet.
  • Polar Bear - 8.4 feet.
  • Asiatic Black Bear - 5-7 feet.
  • Giant Panda - 5 feet.
  • sloth bear - 5-6 feet.
  • Sun Bear - 3-5 feet.
  • Spectacled Bear - 7 feet.

In comparison, the length of an American bison is nine feet; elephant eleven feet; killer whale thirty feet; mountain lion eight feet; and a Siberian tiger thirteen feet long.

bear color

Coloration of bears varies widely between species and within species. Color changes are not uncommon, due to maturation or seasonal fading and shedding of individual bears, or due to the angle and intensity of natural light at the time. Variations can include completely different colors or different shades of one color. (The color of the undercoat usually stays the same while the top coat changes.)

American black bear cubs from the same litter may be different colors, changing from brown to black as they mature, or the opposite may occur. They may molt before they are one year old, or at two and three years of age.

A bear's undercoat may be brown while the outer hairs are black, and some bears are entirely solid color. Several bear species have yellowish or whitish breast markings on many individuals, while the breast marking or medallion is found on all members of the tropical bear family - sloth bears, sun bears, and spectacled bears. Markings vary in shape and size.

Albinism: Although extremely rare, albinism does occur in bear species. A "partial" white-chested, white-forefeet American black bear was observed in Wyoming in 1948. A whitish American black bear is recorded with four cubs: one brown, two black, and one true albino. In Oregon, an American black bear had a light chocolate brown head and feet while the rest of the body was cream (not a true albino).


In general, bear skulls are massive, typically long, broad across the forehead with prominent brow crests, a large jaw hinge, and with strong jaw muscles and wide nostrils. Combined with the fangs, the structure of bear skulls is highly carnivorous, albeit with omnivorous modifications.

The skull can be an animal's most important feature, housing the brain, providing an important protective and feeding feature (mouth with teeth), and containing sensory communication skills. "Bear skulls undergo a series of changes from early life to old age, and in most species they do not reach mature form until they are seven years old or older," noted C. H. Merriam in North American Fauna, Biological Survey, 1918.

Diet and other eating habits influenced the individual development of the heads and skulls of each species. . . are influenced by the teeth and jaw muscles," write Paul Shepard and Barry Sanders in The Sacred Paw." . . [Skulls] are shaped to anchor the appropriate muscles. Because of the strong jaw muscles [the spectacled bear] uses to crush palm nuts, its skull shape is unusual and closely resembles that of the giant panda, which has massive molars for crushing bamboo shoots.”

Brown bears don't typically bite to kill, but rather gnash and gnash their massively muscled teeth to get the job done. Polar bears are more carnivorous than other bears and will bite to kill; Their skulls are specially shaped for the appropriate teeth and muscles to hold, slice, and slice through their prey. Each of the eight bear species has its own distinctive skull shape and size.

  • American Black Bear – Broad and narrow snout; large cheek hinge; female head can be thinner and more pointed
  • Brown Bear - Massive; heavily built; large in relation to body; high forehead (rising steeply); concave (uneven surface); domed head; long snout; flat tip of the nose; ears barely perceived as lumps; tiny eyes
  • Polar Bear - Large; small in relation to body; far away; long muzzle (warms the air); Roman nose; big eyes
  • Asiatic Black Bear—Large; sloping forehead
  • Giant Panda – Huge; broad snout; widespread zygomatic arches; built for the attachment of powerful jaw muscles; short snout
  • Sloth Bear—Dick; long snout; small pine; bulbous snout; wide nostrils
  • Sunbear - Broad and flat (like non-bear); short snout.
  • spectacled bear - wide; short snout; lower jaw shorter than upper jaw (overbite); unusual skull shape; resembles the giant panda; narrow and long young and female skulls

The classification of animals is based primarily on skulls ("... details of the skull and leg bones are the usual criteria for biologists," note Shepard and Sanders) and has led in part to the "splitting" of bear species. Skull size is also the criterion for North America's "record size" bears.


A bear's teeth, combined with paws and claws, are its primary defense and foraging tools. The teeth are large and although they are originally carnivores, they are adapted to an omnivorous diet of meat and vegetables. The main difference between carnivores and omnivores is the molars, which are broad and flat in bears. Dentition - the size, shape and use of teeth - and jaw muscles affect the size and shape of a bear's head.

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Bears have forty-two teeth, except for the sloth bear, which only has forty. The permanent teeth are usually in place when the bear is about two and a half years old. In each species, the characteristics of the four types of teeth - incisors, canines, premolars and molars - vary depending on diet and habitat.

  • American Black Bear - Premolars and molars for grinding
  • Brown Bear – Flat, broad crowns on molars; Premolars and molars for grinding
  • polar bear - canines larger and longer than other bears' molars, smaller than land bears; molars more likely to shear; Premolars more for biting than grinding


A bear's paws are important for locomotion (walking, running, climbing, swimming), killing, eating, digging, lifting, scratching, pulling, turning, feeling, and defending. Bears walk plantigrade like humans, paws with durable pads on the ground and front paws with pigeon toes turned inward. A bear's heat loss (heat regulation) occurs primarily through its paws. "All the pads are lined with hard, calloused epidermis over a substantial mass of hard connective tissue," describe Tracy Storer and Lloyd Tevis inKalifornischer Grizzly. "This foot blanket is the robust, self-renewing shoe."

Bears have relatively flat feet (paws) with five toes, except for the giant panda, which has six. The hind legs are larger than the front legs and resemble human feet, except the "big toe" is on the outside of the leg. Bears are known for their dexterity with their front paws; You can pick pine nuts from cones, unscrew lids from jars and gently manipulate other small objects. "Although seemingly clumsy and clumsy, the grizzly bear is truly one of the most agile of animals," observed Enos Mills in The Spell of the Rockies. “I am always amazed at . . . the lightness of [the] bear's touch or the dexterity of movement of its front paws."

The claws are curved, longer on the hind legs than on the front legs, and unlike cats, are not retractable.

carry vision

It has long been thought that bears' eyesight is generally poor. However, recent studies have shown that it is quite good, although there is still much to be learned about each species' visual abilities.

Bears' eyes are generally various shades of brown, are small (except in polar bears), have round pupils (except in giant pandas, which are vertical slits), and are set wide apart and forward. Important and useful power tools, they reflect and reflect the faintest glow of the moon.

Bears approach objects due to myopia and stand upright to increase their range of vision. Possibly the most specialized eyes, polar bears offer highly adaptable and excellent vision that surpasses that of other bear species. They are large - almost the size of human eyes - and they have an extra eyelid to filter out the glare from the snow. Depth perception is excellent and they can see well underwater due to the nictitating membrane that protects their eyes and acts as lenses. Polar bears' eyes adapt to a variety of light conditions, including darkness for nighttime hunting or in dark winter weather. "The pictorial world of the polar bear is characterized by intense, blinding sunlight, contrasted by long, dark polar nights," reports Thomas Koch inThe year of the polar bear. “Days are usually punctuated by snowfall, hail and strong and constant winds. When these factors are present, the bear's vision rarely provides ideal conditions for seeing its surroundings. When polar bears travel on ice in good conditions, they can identify stationary objects lying on the ice up to a mile away.”

However, a whaler's diary describing a blind polar bear shows that good eyesight is not always necessary. "Based on the bear's eyes, the men assumed that the bear had been blind for a long time," reports Koch. Although the bear was blind, it was still fat, suggesting it successfully hunted using just its hearing and smell.”

The ability to distinguish colors and activity in all lighting conditions (day and night) are excellent indicators of good vision. Some biologists believe that bears' eyesight is at least average, and at least two have expressed the thought that while bears act as if they have poor eyesight, they may not trust their eyes as much as their trusty noses. "A lot of the anecdotal information about bear sighting," according to Paul Shepard and Barry Sanders in The Sacred Paw, "assumes that the animal approaches foreign objects because it can't see them well from a distance, but crows and Coyotes do the same. same thing. and no one doubts his eyesight.”

wear hearing

Bear ears vary between species, both in size and their position on the head. They range from large and flabby to small and barely visible, and from well in front of the head to all the way down and back.

In general, a bear's hearing is fairly good to moderately good. "Hearing in bears is probably good," explains Stephen Herrero in Bear Attacks, "although most of the evidence is anecdotal."

Bears, he also notes, "...probably hear in the 16-20 megahertz ultrasonic range, maybe higher." an important tool in finding subterranean prey such as squirrels, ground squirrels, mice and voles, bears recognize and attack with remarkable accuracy.”

"At 300 meters [328 yards]," Shepard and Sanders write, "the bear can hear human conversation and respond to the click of a camera shutter or the cocking of a gun at 50 meters [54.7 yards]."

"Bears' hearing is not as obvious as sight and smell," notes Adolph Murie in The Grizzlies of Mount McKinley. "While it's not a prominent part of their activities, I believe bears have good hearing."

ability to smell

Whether flush with the ground or raised in the wind, a bear's snout holds the key to the environment. Smell, Herrero writes, is the basic and most important sense a bear has. A bear's nose is its window to the world, just like our eyes.

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The keen sense of smell - the olfactory awareness - of bears is excellent. No animal has a more keen sense of smell; It allows for locating sexual partners, avoiding humans and other bears, identifying cubs, and locating food sources.” . . the nose provides the primary sense in searching for food,” notes Paul Schullery in The Bears of Yellowstone. The bear's nose is somewhat "pig-like", with a pad extending a short distance in front of the snout.

A bear has been known to detect a human scent more than fourteen hours after the person has walked a trail. "Bears' sense of smell is among the most keen in the animal kingdom," says George Laycock in The Wild Bears. "A black bear in northern California was once seen traveling three miles in a straight line upwind to reach the carcass of a dead deer."

Polar bears' sense of smell is possibly the keenest - able to spot a seal several kilometers away - and, as Domi correlates, ". . . male polar bears march in a straight line over pressure ridges of high ice. . . up to 40 miles to reach prey they've spotted."

A closely related ancient Indian proverb perhaps best describes bears' sense of smell. "A pine needle fell in the forest. The eagle saw. The deer listened. The bear smelled it.


Bears possess tremendous power, regardless of species or size. A bear's strength is difficult to measure, but observations of bears moving rocks, carrying animal carcasses, removing large logs from the side of a hut, and digging cave-like holes indicate tremendous strength. No animal of the same size is so powerful. A bear can kill an elk, elk, or deer with a single blow to the neck with a powerful front paw, then lift the carcass into its mouth and carry it great distances.

"Strength...matches his size," describes Ben East in Bears. “He has a very powerful build, a heavy skeleton covered with thick layers of muscle as strong as rawhide rope. He can hook his long, bearlike foreclaws under a slab of rock that three grown men could not lift, and could turn with almost no effort..." "...a brown [bear]...carried a thousand-pound ox half a mile over one almost vertical mountain, most of it through tangles of alder with trunks three or four inches thick.”

Strength and power are attributes not only of large bears, but also of young ones. The author observed a year-old American black bear “backhand” flipping a flat rock (between 310 and 325 pounds) with a single front paw while searching for insects. The bear was captured in a handling operation the next day and weighed 120 kilos.

bear smell

Bears have a specific smell, as do other animals, including humans. However, a bear's scent is quite distinct, though not necessarily repulsive (depending on the individual's nose), and is considered by many hunters to be the easiest thing for a dog to track. the vent hole.

The American black bear has a slightly different odor than the brown bear, which smells like musk and powdery mildew, according to a bear biologist. Scientists, naturalists, hunters, and others who have experienced a bear's scent agree that it may never go unnoticed by them again.

body temperature

The normal body temperature of bears is around ninety-eight to ninety-nine degrees Fahrenheit. Temperatures, like other mammals, vary based on individual differences and activity levels. Temperatures are usually taken while bears are immobilized (for obvious reasons) and under physical and psychological stress, resulting in elevated temperatures and making it nearly impossible to determine a "normal" temperature. However, two adult male brown bears in captivity have recently had their temperatures taken under "normal" circumstances. They each swallowed a small temperature-sensitive radio transmitter that was placed in their food. Their recorded body temperatures ranged from 98.5 to 99 degrees Fahrenheit, with an average temperature of 98.9. Interestingly, while still in their stomachs (before being excreted with other feces), the transmitters were fed frozen fish, after which their "stomach" temperature dropped below eighty degrees.

A bear's temperature can drop a few degrees when the animal sleeps at night or rests in a snowdrift or on a cold bed. A hibernating bear's temperature drops relative to outside and den temperatures, but it appears to have a safety mechanism by not dropping below about eighty-nine degrees Fahrenheit.


Bears, like all mammals, need to regulate their body heat. A bear's fur is an extremely effective winter insulator, retaining body heat while absorbing heat from the sun. However, it does not allow adequate cooling in hot weather. Because they lack sweat glands, bears must cool down through several unique methods that dogs share.

  • Balancing energy expenditure and food intake
  • Rest in shady beds and cool summer caves
  • Lie down with your stomach in full contact with the cool earth
  • giving off heat by saliva, panting like a dog; via the paws, which represent the greatest loss of heat, as the pads are well supplied with blood and lie flat on the cold ground - and through sparsely haired areas such as the face, ears, nose and the insides of the hindquarters of the paws
  • The muscles behind the shoulder contain a large number of blood vessels and act as radiators.
  • Shake off water if it comes from a lake or stream
  • Spread out in snowfields or patches of snow
  • Spread your legs (thighs) wide
  • immerse in water
  • Take mud and dust baths

Like other bears, polar bears face overheating, but they also need extra warmth during the sub-zero temperatures of the Arctic winter. They have three to four inches of subcutaneous fat on their buttocks and back, which provides extra insulation. However, they mostly bask in the sun, and their outer coat acts as a unique heat transfer system. Polar bear hair, according to Charles Feazel inWhite Bear: Encounters with the Master of the Arctic Ice, with " empty core in the middle of each strand. Each hair acts as a light trap, a channel that carries the sun's rays...the last few inches of its dark skin. The polar bear's skin is one of the most efficient UV [ultraviolet ] absorber of nature Ultraviolet light penetrates clouds, allowing Nanook's efficient solar collector system to function for seven days on cloudy days. In addition, a polar bear's long snout warms the cold arctic air as it inhales.

According to George Schaller et al. one ". . . short, thick coat [which] provides excellent insulation; the animal willingly sleeps in the snow. The hair's dense and oily texture likely prevents moisture from penetrating the skin, an important adaptation in a wet, cold environment. And the hair has a springy quality; are resistant to compaction, which reduces heat loss when the panda lies down in snow or on cold ground.”

A sloth bear, with its belly and almost bare paws, is quite heat tolerant.

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A normal heart rate for bears is 98 beats per minute while awake and walking, but increases with activity and drops to 40 to 45 beats per minute during nighttime sleep. Some bears' heart rates slow to eight to ten beats per minute when resting in a snowdrift.


Bears' lungs are relatively large and their breathing rates range from six to ten breaths per minute at rest, forty to eighty breaths per minute during heat and panting, and sometimes in excess of a hundred breaths per minute during extreme exertion. Oxygen uptake (rest) is reduced by about half during hibernation.


Bears have terminal sensory organs and experience painful stress from both internal and external sources. Bear's pain is not necessarily comparable to human's, which may be more complex. In general, they don't seem to show any overt reactions like humans do. Bears sustain numerous injuries as a result of their very existence and have been likened to professional soccer players who "live in a world of constant pain".

Persistent pain creates irritability and many "annoying" bears who show their discomfort through aggressive behavior toward humans and other bears. They are found with abscessed teeth or other wounds. Your wounds or other problems may be natural or human in origin:

  • Abscessed teeth (seem to have more problems with their teeth than many other animals, probably due to sugary food)
  • External parasites (including bees, which cause obvious sting pain when bears look for "hives")
  • Fight with enemies or other bears
  • gunshot wounds
  • Internal parasites (tapeworms cause significant distress to bears)
  • Loss of teeth with age, resulting in an inability to eat

"Although bears can cry in pain when stung by angry bees, they persist until the entire honeycomb is eaten," describes Terry Domico in Bears Of The World.

digestive tract

Bears have a simple intestinal tract, with the colon being the primary site of fermentation. They have long intestines to help them digest grass, but they don't digest starch well. Its small intestine is longer than that of true carnivores, and the digestive tract lacks the characteristics of true herbivores.

A bear's barrel-shaped body is thought to indicate a long intestine. Brown bear gut length (overall and small) is greater than that of the American black bear and giant panda. Polar bears have the longest intestines.

Giant pandas' short intestines result in poor digestive efficiency. Only twenty to twenty-five percent of their food is digested; Therefore, they need to eat large amounts - 10 to 20 kilos of leaves and stems a day - to get the minimum amount of energy. They produce substantial feces, mostly undigested bamboo, which passes in just five to eight hours.

A solar bear cub's food system needs external stimulation for the first few weeks after birth to allow the processes of urination and defecation to take place. The sow licks the young to provide this simulation. The American black bear also sometimes has to play this role.


Scat or feces are the excrement of animals. Eschatology is the scientific study of feces; Scientists collect and thoroughly analyze bear droppings to determine many things about bears, including what they eat, how much of each type of food, and what time of year they eat the specific food. The information provides further insight into bears' needs and activities, and assists in the proper management of their habitat.

Bear droppings are also good for the earth. It disperses and fertilizes the seeds of the plants eaten by the bear, providing humus that enriches the soil.

For the traveler in bear country, the sighting of bear droppings inspires both excitement and fear: Finding a sign of a bear is exciting, but at the same time, not knowing its exact location creates moments of dread. But bear droppings can also answer questions – how long has the bear been here, how big is it and what has it eaten?

In retrospect, some of the above facts may seem dry and of little importance to Bowhunter. However, in conjunction with other information on habitat, behavior and diet; Some of these facts provide keys to locating the bear on your bear hunt.


And just because I can, below is Lethal Injection Outdoors' Wayne guest on his successful black bear hunt in Saskatchewan. Robert Hoage

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