American Bison(Bison Bison Americanus)
American Bison. Source from:

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Bison bison americanus, also known as, The American Bison, is the largest land walking animal in North America and Canada. The Latin name, Bison bison americanus is quite self explanatory, where Bison means any wild ox in general and americanus simply means American. Male American Bison weighs between 1000-2000 pounds and can reach to more than 6 feet tall and 3 meters long, whilst female bison are generally smaller in size which weights between 800-2000 pounds and stand 5 feet tall from hoof to shoulder. Both male and female bison share the similarity of having brown coloured long and shaggy fur, a mane and a beard growing under their chin. Another shared characteristic can also be identified from their large sized head, with a pair of black coloured short horns and a hump on their shoulder.

Scientific Classification

Labeled Diagram of American Bison

Figure 1: American Bison's labeled photo. Source from:

Figure 2: Distribution range of American Bison in North America. Source from:


Historically, American Bison ranged all the way from Northern Mexico to Alaska, being the widest nature range of any North American herbivores. However, due to human encroachment, most of the American Bison today occupy less than 1% of their former range, restricting to a few national parks and other wildlife areas near the river and Great Plains in North America. The total number of American Bison today ranges around 350,000 when originally it was in millions.

Wild Life condition (Great Plains)
Figure 3: American Bison grazing the Great Plains in North America. Source from:

The Great Plains of North America shaped like a triangle, covering 1.4 million square miles of land. The American Bison spread equally in herds around the Great Plains in North America, where there are sufficient grassland and meadows as food supply for them. They move near to the rivers together when they need water. These animal share the same diet as rabbit and water buffalo. Climate in the Great Plains is really wild, having extreme temperatures during summer and winter, with a really high wind speed due to the open lands. Because of the extreme temperature in the Great Plains, the American Bison will shed their fur during summer to cool down and will re-grow their fur during winter to keep warm. In more southern side of the Great Plains, the American Bison inhabit the long and short grass prairies and parklands into the foothills of the Rocky Mountains.

Yellowstone national park
Figure 4: Bison grazing in Yellowstone National Park in North America. Source from:

The Yellowstone national park is the world's first national park established during 1872 aiming to protect American's vanishing wildlife. It is also the most intact ecosystems in North America containing both predators and prey. Most American Bison inhabit there, with the population of around 4000, way more than from the wild. Weather condition in the national park is as wild as the Great Plains with very hot summer seasons and freezing winters. Fortunately, snowmobiling activities will be done inside the park during winter to groom down the snow for the bison, so that they can save up the energy without having to travel through the deep snow. Even though many projects were done aiming to sustain the lives of the American Bison, but this did not stop the disease called brucellosis from out breaking in Yellowstone National Park during recent years. This type of disease causes abortions to bison as well as other elk around the area. However, there are no cases of brucellosis infected animals in the wild, so it is easier to cure the disease within the area.

Structural Adaptation

1. Large body size - The American Bison spend most of their life living in open land areas without a shelter. Due to this fact, this type of herbivore has evolved into developing a large and heavy body in order to survive in the open areas. Unlike the animals of having a small body size, that are capable of hiding themselves under shelters away from their predators, there is absolutely nowhere for Bison to hide, especially in the open lands of Great Plains. However, the large body structure is one of the physical adaptations that help the American Bison to travel through the open lands of North America. Prevention is the best form of protection; this statement certainly applies onto the American Bison, when potential predators recognize their huge body size that they would rather choose to walk away than attacking them. The environmental pressure of rapidly increasing wolf packs during winter and increasing number of grizzly bears during summer forces the American Bison to evolve into developing a large body size, in order to protect themselves while traveling through the Great Plains of North America.

2. Strong short legs - Each American Bison has 4 even toed short legs to support their heavy body. These legs play a very important role to the bison considering they are constantly walking throu
Figure 5: Strong legs supporting heavy American Bison. Source from:
gh the plains. Sometimes, the bison will eat while they walk in order to cover more grassland for food; therefore the strong and steady legs are very important to them considering they are such heavy weighted animal. Another function for these strong legs is to run. The American Bison's legs are able to support 2000 pounds of body weight and run at the speed of 40 miles per hour, even faster than their biggest natural predator, the grey wolves. The environmental pressures that force the bison to develop such strong legs are the food supply and their predators. The bison cannot inhabit in a set area, they are to move constantly from one area to another in order to find new grassland for food. Since bison live in herds, they cannot stay in one area for too long because all the grass will be eaten really quickly, therefore they have to move into new plains before the grass runs out, and that requires their strong short legs to move from places to places. Another environmental pressure is from their predator, Grey Wolves. These Grey Wolves attack in packs and can take down any old or new born bison. This forces the bison to develop their strong legs in order to flee from their predators. Having shorter legs compared to their body size can also create a lower central gravity so that they are more balanced and would not fall on their sides as easy. This is very important to the bison as it is really difficult for them stand back up after falling, and if they fell down while the wolves are attacking them, it often result in death of the bison.

Behavioral Adaptaion

1. Wallowing - Wallowing refers to dust bathing, which means rolling the body against dust and mud from the ground. This is the most common activity amongst the American Bison during daytim
Figure 6: American Bison wallowing on dirt. Source from:
e. A bison wallow is a shallow depression on the soil, caused by the American Bison after rolling itself onto the dust or mud patch, creating a smooth depression on the ground. There are various reasons for American Bison to wallow on soil. Past researches show reasons for American Bison to wallow are for grooming their fur, a form of rutting behavior, social behavior for group cohesion etc. However, the main purpose for wallowing from the American Bison is to actually brush away the biting insects in order to be relief from skin irritations. The motion of rolling onto the dust can clear out biting insects on bison's body during summer seasons. The act of wallowing relates to the environment of which the American Bison live in. During summer time in North America, flying insects usually conquer the skies of the Great Plains and feed on the blood of the American Bison. This causes skin irritations for the bison and therefore they develop the act of wallowing, in order to relief the itchiness from their body and to scrub away the insects hiding under the long and shaggy fur.

2. Bison calves able to walk within few hours after birth - April is when the calving season be
Figure 7: Bison calf learning how to walk. Source from:
gins after the 9 months gestation period. However, bison calves can also be born at any other time of the year. A baby bison will wobble on its feet after birth, but it only takes few hours for it to start walking normally. The bison calf will stay closely to their mother for the first few weeks and the mother would look after its calf carefully. Living in the Great Plains is full of danger, especially for these new born bison, they are the targeted prey of the wolf packs. Being able to learn how to walk within a short time certainly helps the calves to stay after from the predators. Also, the American Bison travel constantly in herds, it is important for the new born bison to keep up with the rest of the group. The environmental pressure that forces calves to learn walking straight after their birth is the natural predator. If they cannot keep up with the herd of bison, there is a great chance of being hunted down by the Grey Wolves or Grizzly Bears, as well as other potential predators.

Physiological Adaptation

1. Acute sense of hearing - The American Bison evolved into having poor eye sight due to their fur for surrounding their eyes. However, without having to use their eyes, the bison can detect the surroundings with their acute sense of hearing. The American Bison can hear sounds from 3km away, knowing what types of animal are near their herd. This can help the bison to detect danger from their predators, being able to hear the footsteps from wolves or bears in order to prepare their fleeing direction. The environmental pressure for acute hearing is to detect where predators are coming from. Since the American Bison has very bad eye sight, they are not able to observe the surroundings clearly. The job of detecting the surroundings in the open plains is then left for the ears to do.


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