How Big Do Beavers Grow?


Beavers are North America’s largest rodents and the second-largest after capybaras of South America. Compared to rodents such as rats and mice, beavers are huge.

Beavers grow continuously throughout their lives, with male and female beavers growing to the same weight and length. They reach up to 70lbs but have been known to reach 100lbs. They can reach a length of over 40 inches, including the tail. Beaver kits weigh up to one pound when born and are about 7 inches long.

Beavers have thick fur, heavily webbed feet, and tails that are almost completely covered with scales. With strong jaws and powerful teeth, they gnaw through trees to build homes and dams.

Beavers continuously grow, and they can change their environment to suit them.

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Beaver couple

How Big Does A Male Beaver Grow?

The American male beaver has an overall length ranging from 25 to 39 inches. Their healthy weight varies around 24 to 71 lbs, with an average weight of 55 lbs. The tail of a beaver contributes significant length and weight. The tails of beavers range from 7.75 to 14 inches long. 

How Big Does A Female Beaver Grow?

The weight and size of a female are almost the same as males. In some cases, they are even larger than males, something that is extremely uncommon among mammals. 

How Big Are Beaver Kits?

Baby beavers are called kits. There are usually two to four born from one litter. They are born with the ability to swim but typically don’t do much for the first few weeks.  Kits are tiny and easy prey for predators.  They weigh around 1 lb at birth and are about 7 inches long. When kits become adults, their larger size is ideal for helping scare off predators.

There are a few differences between Eurasian kits and American kits.  American kits are weaned after two weeks, but Eurasian kits are weaned after six weeks. Eurasian kits weigh 8.1 to21 ounces, while American kits weigh around 9 to 21 ounces. 

Kits leave home at the age of two and start mating at three. Beavers mate during the winter months.  Eurasian beavers are pregnant for 2 to 4 months, while American beavers are pregnant for about 3 and a half months.

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Do Beavers’ Teeth Grow Forever?

Beavers have massive teeth that continue growing. Their upper incisors range from 20 to 25mm, and their growth isn’t hindered. Beavers don’t exhibit the best dental hygiene, and their teeth are usually orange due to the iron in them. 

Like most other rodents, their teeth are powerful. The strength is primarily because the enamel of a beaver’s tooth contains iron. This makes them extremely sharp and durable.

Beavers’ teeth curve backward, making it easier to cut wood. The growth rate of their teeth is about 4 feet per year.  However, the teeth wear down through gnawing.

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The orange enamel wears away at a slower rate than the white dentin along the back.  Beavers self-sharpen their teeth every time they gnaw a tree.

A study in Science Direct about the seasons and their relation to incremental growth rates in beavers revealed a connection between the time of year and the growth rate of beavers’ incisors. The sample of beavers used for the study was harvested in fall and winter. 

The growth rate of the upper incisors differs from the growth rate of the lower incisors. The top incisors grew less during late summer and early fall. The lower incisors did not show much difference in growth between seasons. The top incisors are used to estimate which season a fossilized beaver had died.

What is the Largest Beaver on Record?

The largest North American beaver ever recorded weighed 110 pounds (50 kilograms.) This beaver was from Wisconsin, and it was caught in Iron County.

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Giant Prehistoric Beavers

Although they didn’t feature the classic flat tail, the Ice Age’s giant beavers had remarkably similar characteristics as their modern counterparts. Widely known as Castoroides, these species were even larger. 

According to scientists, they were 8 feet long and almost 200 pounds. Like their modern counterparts, beavers of the ice-age lived semi-aquatic lives.

Do Beavers Grow Forever?

Both male and female beavers grow throughout their lifetime and weigh up to 60 or 70 lbs when there is enough food. In most cases, they live up to 25 years in the wild. The lifespan is reduced by a few years when they are held in captivity. 

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Beaver trees

Being semi-aquatic animals, beavers require a proper diet to survive properly.  This is a reason they are extensively found among freshwater ponds, rivers, marshes, and swamps.  

Whilst American beavers are found throughout North America, they try to stay away from deserts and settle down in marshy zones. Over the last fifty years, the number of beavers has increased around lakes, swamps, and woods.

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Are North American Beavers Larger Than European Beavers?

North American beavers and Eurasian beavers are similar, with European beavers being slightly larger.  Beavers adhere to a zoological principle known as Bergmann’s Rule, named after its founder, Carl Bergmann. The rules state that mammals living in colder locations are larger than those in warmer locations. 

This is evidenced by the fact that  North American beavers are larger, weighing approximately 45 lb. An adult North American beaver’s total length is 29–35 in, with the tail adding an extra 7.9–13.8 in.

Age plays a factor, with some older beavers reaching larger than average size and weighing from around 88 lb to 110 lb.

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There are small physiological differences between the North American beavers and their Eurasian counterparts. The most striking is that the American beaver has longer shin bones. 

Longer shins allow them more flexibility and range when moving on two feet, which has the knock-on effect of making it easier for them to utilize their hands to carry out tasks.  

Other differences are that the American beaver has a smaller head, shorter and broader muzzle, thicker and longer underfur, differently shaped nasal openings (square for American, triangular for European), and broader, more oval tails.

Interbreeding between the two species is not possible due to a difference in the number of chromosomes carried by each beaver species.

Do Beavers Grow All Year Round?

Beavers reduce in size during the cold winter months and grow during summer.  A study was published in the Journal of Mammalogy, Volume  78, Issue 3, regarding body mass and tail size. 

It concentrated on 33 colonies found in two national parks and monitored their growth over seven years.   The study found that the growth rate was affected by the weather, pond location, age, and if the colony had kits.

During winter, both adults and babies reduce the tail size and body mass, particularly those living in young colonies.  Beavers grow more during the summer, and their tails grow larger too. 

What is a Beavers Growth Rate?

In a study conducted by Arthur Pearson on the growth and reproduction of beavers, they were noted to grow at a rate of about 0.058 lbs per day.

How Big is a Beaver’s Tail?

Beavers have flat tails that are 15 inches long and almost 6 inches wide. This massive, broad tail is handy when the species are on land. Beavers stand on their two hind legs to gnaw tree trunks and branches. The tail acts as an added leg, allowing them to balance better.

The tail is also used as a lever when beavers want to drag bulky, big, and heavy branches along the bank or by the side of the dam.

Beavers will slap their tail on the water to warn others about impending danger, and they also assist them while swimming.

While the tails of beavers are an excellent tool, there’s a common misconception regarding their use. According to the Washington Department of Fish and Wildlife, the tails aren’t used for plastering mud on dams. While this is a common belief, it is entirely inaccurate.

Beavers store energy in their tails in the form of fat and increase their fat supply in colder weather by as much as 60%!

How Big are Beavers’ Lungs?

Beaver’s lungs are considered to be extremely large for their body size. Beavers are known for the ability to store extra oxygen in their lungs. Their lungs and livers allow them to store more oxygen than other mammals of a similar size. 

They are also capable of slowing down their heartbeat as they are swimming. This enables them to save a significant amount of energy.  These adaptations allow beavers to stay submerged entirely underwater for close to fifteen minutes.

The slow heartbeat is also the reason why they can swim half a mile underwater without resurfacing. The beaver would not be able to live its semi-aquatic lifestyle without its oxygen storing capacity. 

The respiratory system is almost similar to any other mammal. Air passes through their nostrils, move along the pharynx and finally reach the larynx.

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After the air enters the trachea, it reaches the two bronchi. The bronchi then separate the air in the lungs, making way for the exchange of gas. 

Blood pumped through the heart transfers the oxygen while relieving its cells from carbon dioxide, which is eventually discharged by exhaling.

Beaver print

How Big are Beavers’ Footprints?

Beavers have larger webbed rear feet than their front feet and resemble a raccoon’s. The front feet are not webbed.  The back foot is about 6 inches long and has a split toenail, which beavers use for grooming, while the front feet are about 2.5 to 3 inches long.  All beavers feet have five digits.

How Big Are Beaver Dams?

Beaver homes are called lodges and are constructed in a pond made by a dam. These are built from mud, sticks, grass, and moss. There are two types of beaver dams. The first is a dome-shaped lodge, while the other is a den on the bank.  The type of lodge beavers build depends on the water speed and water levels. 

Simple bank dens are built-in fast-moving water, while domed lodges are built in slow-moving water. Beaver lodges have underwater entry points to allow them to get in and out. 

Beavers can build a lodge in a few days, and they can be as large as 20 feet wide at the base and 10 feet high.  They can also be as large as nearly 40 feet wide and 16 feet tall.  You can find these homes situated alongside rivers, lakes, streams, marshes, and ponds.

Beavers are social creatures, and one lodge can house up to 18 beavers, with 2 to 4 adults, their newborn kits, plus older kits that have not left home. Beavers re-use and ‘renovate’ their dens annually by adding more twigs, branches, and mud.

Beaver dam

Just like beaver lodges, beaver dams are also dependent on water speed and water level. These dams are built in shallow, slow-moving water and can be 6 feet tall, 4 to 6 feet deep, and 5 feet thick. 

Beavers use trees to build their dams.  Depending on the size of the tree, they can fell it within a few minutes.

The length of the barrier depends on the stream’s width, with the longest beaver dam found in Three Forks, Montana. It is 2,140 feet long, 14 feet high, and 23 feet thick.  This dam can be seen from space.

How to Watch Beavers?

Now that you have learned about beavers and their size, you might want to see them in real life. The following are a few tips for when you want to spot nature’s little engineers at work:

DO

  • Keep your distance. Do not crowd the animals you are observing.  Allow them space to carry on with their daily business without interference or creating an atmosphere of anxiety by keeping a minimum distance of about 33 to 50 feet.
  • Be aware of signs of distress. Animals may become stressed out if when being observed for long periods. Beavers will bang their tails to let you know they are getting agitated. Keep a lookout for signs of distress and move on.
  • Make pond sitting a habit. If you re-visit the same pond regularly, the local beavers may become accustomed to you.  You will enjoy a better experience watching them as they interact with each other.

DON’T

  • Don’t hide behind bushes. Beavers will be able to sense your presence. Keep your voices low and stay around 15 feet from the shore of the pond.
  • Don’t try to interact with the beavers or other wildlife. It is best to observe them at a safe distance.
  • Don’t feed the animals. Human food is not suitable for beavers.
  • Don’t touch or pick up any of the animals. They can be extremely dangerous.
  • Don’t let your pets, such as dogs, run wild around the beavers. Not only may this panic the beavers, but they may also attack, causing severe damage.

Bonus Tip – Drive Safely

If you are lucky enough to spot beavers while driving and you wish to stop, make sure to indicate that you have stopped other drivers by putting on your hazard lights. Ensure that the area you have pulled off into is a safe place to stop and check for oncoming traffic before crossing the road.

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Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Nature.

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