How Big Are Bisons? (What Affects Their Size and When Do They Get So Big?)

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​Few animals in North America can match the weight and size of the bison, making these mighty beasts among the continent’s largest animals. 

When they reach full size, a bison can tower over almost all other American wildlife, but something like this doesn’t happen overnight. Getting so big requires many factors working in their favor. Things that can seriously affect the size of a bison, include genetics and the environment.

So, how big do bison get, and what allows them to get to that size?

Join us in Floofmania as we explain how big these bovine giants are and what affects their growth.

How Big Is A Full Grown Bison?

Plains Bison are not only the largest land mammal in North America, but they are also the largest land animal on the continent. 

Males tend to be larger than females, with the average bull reaching up to 6.5 feet (2 meters) tall at the shoulder and being 9-11 feet (or 2.7-3.4 meters) long. To put that into perspective, that size is comparable to the average car.

Females tend to be smaller, reaching only about 4 or 5 feet (1.2-1.5 meters) tall and 7-8 feet (2.1-2.4 meters) long. While somewhat small for a bison, that is still massive compared to most animals.

The bison’s tail makes up about 11 inches or a little less than a foot.

How Much Do Bison Weigh?

Aside from being large, bison are also incredibly heavy, with the average bull weighing about 2,000 pounds or 907 kilograms, which is almost a tonne. 

As with their size, females tend to be much lighter than males, and the average cow weighs half of that at 1,000 pounds or 454 kilograms. While that is a big difference, these bison aren’t light by any means and could still outweigh most things in your house. 

What’s The Largest A Bison Can Get?

Some bison have reached nearly 11 feet in length while being over 6.5 feet tall at the shoulder. The largest recorded bison was said to weigh over 3,000 pounds or 1,400 kilograms.

However, pioneers in the 1800s made many unofficial claims of seeing or owning bison far larger. One of the most fantastic claims was that some pioneers claimed to have found a bull that weighed nearly 3,500 pounds. If that were true, it would make the bull heavier than an SUV.

While that would be impressive, you should take these claims with a grain of salt. They are unofficial because they depend primarily on flimsy evidence that cannot accurately verify the claims. For all we know, the pioneers might have been wrong or intentionally faked results to gain fame.

Did Bison Use To Be Bigger?

Although the idea of giant bison is mostly false, there is a grain of truth to pioneers’ claims of giant bison.

Studies have shown that bison today are noticeably smaller than those that lived over a century ago, and it is suggested that bison now weigh at least 20 pounds less than they used to. While not a lot at the moment, this number is slowly increasing and can become much higher over time.

This change is often attributed to climate change, a growing environmental problem that can affect animals in various ways. For bison, it has affected the population by causing them to shrink.  

As the Earth’s climate warms, grasslands, where bison get their food, become less productive and provide fewer nutrients. Many young bison, who rely on grass as the main part of their diet can suffer from nutrient deficiencies.

Diet plays a huge part in growth and development, so young bison will not be able to grow as much with this diet.

Many people, including ranchers, are trying to combat this phenomenon by providing bison with a more diverse diet. Researchers are introducing things like shrubs into bison’s diet because these can provide more protein and can help them grow.

Are Wild Bison and Farm-Raised Bison Equally Big?

Generally speaking, animals that live in captivity tend to be smaller than their wild counterparts. 

Some ranches also intentionally grow bison to be smaller than their wild counterparts. The owners do this to make bison easier to manage and less likely to break their enclosures. 

However, other ranches prefer to let bison grow as big as possible to have more meat and produce to sell so they take steps to give bison all the resources they need.

The answer is it can depend on the conditions of the ranches. Some ranches are massive, with hundreds of acres of grasslands that give the bison all the necessary grazing space. Farm-raised bison can reach the same size as wild bison in conditions like that.

If a farm isn’t well maintained or doesn’t offer enough space for bison, it means that bison aren’t in a healthy environment where they can grow. There are two main things on the farm that can affect the size of bison: the availability of resources and the gene pool.

Ranches Need Strong Genetic Diversity

One of the persistent problems with bison repopulation, especially on farms, is the lack of genetic diversity.

With bison herds separated from each other in ranches, they have less opportunity to intermingle and expand the gene pool. Without enough genetic diversity, bison can become inbred, affecting their size and health.

To address this, some ranchers now have breeding programs where new bison are introduced into the herd to expand the gene pool. So if a bison ranch follows some of these programs, it will not be at risk of inbreeding and will grow as normal.

Bison Ranches Need a Lot of Resources 

Aside from genetics, ranches also need a lot of diversity in the resources and food they provide the bison.

With global warming affecting the productivity of grasslands, ranchers need to find other ways to provide nutrients to their herds. One way ranchers do that is to diversify the diet of their bison.

Aside from grass, some ranchers also feed bison helpings of shrubs and bushes, which contain more nutrients and can compensate for the lack of vitamins from grass. This extra nutrient means that bison can continue to grow big and strong.

How Big Is A Bison Calf?

When a bison calf is born, it weighs about 50 pounds on average, though calves can range from 30 to 70 pounds.

While that’s a far cry from the size of their parents, they are still easily ten times the weight of the average human infant. Within the first few hours, a bison calf should already be able to stand; when they do stand can reach up to a person’s waist.

How Much Does Bison Weigh When It Starts Weaning?

By the time they celebrate their first six months of life, bison calves are weaning off their mother’s milk and transitioning to a diet of grass and plants. The result is that growth will speed up as they have more access to a more diverse diet. At six months, bison calves weigh around 300-400 pounds.

Yearlings Can Double Their Weight

After their first birthday, when calves become yearlings, they have effectively doubled their weight from when they were six months old. 

This period is the time for the most significant growth for our young friends as they have fully transitioned from milk. Between their first birthday to reaching 18 months old, bison can weigh as much as 700-800 pounds. By 18 months, bison should also be reaching their adult height.

Do Bison Calves Grow Fast?

It depends on how you look at it. Compared to humans, bison can grow incredibly fast, reaching adulthood in less than two years. Although if you compare them to cattle, bison are not the fastest growers. Their relatives like farm cattle can reach sexual maturity in less than a year.

Still, the amount of change a bison undergoes in 18 months is astounding as they double their height and gain ten times their body weight. Much growth comes after the first six months as calves are weaned off their milk.

When Are Bison Fully Grown?

Although calves stop growing at about 18 months, that doesn’t mean they are adults yet. Instead, this is when calves hit puberty, so while they are close, they are not there yet. This process can last for several months to a year.

Most bison only reach sexual maturity when they are two or three years old. By that point, bison are fully developed physically and mentally and look no different than their parents.

Why Does a Bison’s Size Matter?

Aside from looking impressive, bison serve some essential purposes thanks to their size. Their sizes allow bison to protect themselves and help the environment. 

The Bison’s Size Keeps It Safe

Although bison prefer to rely on safety in numbers, they can take care of themselves thanks to their immense size.

Aside from being big, bison are also strong, and many animals, including predators, understand that and try to avoid them. While some large animals like wolves and bears might try hunting them, bison can defend themselves quite well. 

Bison Can Affect The Environment

The only thing larger than a bison is its environmental impact. Bison are considered a keystone species because of their massive size, which is indispensable for the ecosystem in the plains.

For one thing, bison create makeshift pools along the ground called wallows. These depressions form when bison have their dust baths and compress the loose soil together.

These wallows collect water when it rains which provides much-needed water sources for the animals and plants along the plains. Plants can absorb water from them while amphibians like frogs make their homes in the wallows. 

How Big Are Bison Compared To Other Animals?

Although bison are the biggest animals in North America, they have some rivals, from close relatives to giant forest creatures. 

Cattle

Cattle are some of the bison’s closest relatives and share many similar features, including their size. Average bull cattle are close to the bison, standing at 5.9 feet and weighing 1800 pounds. Cows meanwhile are about 5 feet tall and weigh 900 pounds. Both of them have a length of ​​8.5 feet.

Horses

Horses are another well-known animal in the North American ecosystem, and they have been racing, working on farms, or roaming in the fields for centuries. American Quarter Horses are more lightly built than bison, but still quite big. The average horse is 5.3 feet at the shoulder but weighs 950 to 1,2000 pounds while being 8 feet long.

Moose 

The moose is one of the closest rivals, a bison in size. Like bison, moose can grow to great sizes, with the average bull moose standing nearly 6 feet tall and weighing around 1,000-1600 pounds.

Female moose are a bit smaller, are closer to 5.5 feet tall, and only weigh 600-800 pounds.  They both measure around 7-10 feet in length. 

Water Buffalo

Although often confused with bison, water buffalo are an entirely different species, but both are massive. The average Asian buffalo is 5 to 6.2 feet tall at the shoulder and 8 to 9 feet tall and weighs 1,500-2,650 pounds, meaning some heavier buffalo can outweigh a bison.

Elks

While not as strong as bison, elks are some of the most magnificent animals in the forest and deserve a mention.

The average elk bull measures 5 feet tall at the shoulder and weighs roughly 700 to 1100 pounds, while a cow will measure 4.5 feet, and in terms of lengths, elks can reach 5-8 feet. Elks can reach lengths of 7 or 8 feet on average.

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Author: Quade Ong

Hello there, my name is Quade. I have been a writer for three years but an animal lover for over two decades. I grew up in one of the most biodiverse areas in the world, which has given me the blessing of seeing all sorts of beautiful animals. Now I strive to learn not just about the animals I am from, but those all over the world!

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