How Big Do Beavers Grow?


Beavers are one of the biggest rodents of North America, and the second-largest across the globe, right after capybaras of South America. I wanted to find out how big beavers can grow as I have seen some photos of large beavers recently.

Both male and female beavers grow to approximately the same weight and length. Beavers grow continuously throughout their lives reaching up to 71 lbs and a length including the tail of 39 inches. Kits weigh up to one pound when born.

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 for building homes and dams.

Beavers can grow massively in size, and they can change their environment as very few animals can. Over the next few sections, I discuss some interesting facts about the growth potential of beavers.

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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 beaver are almost the same as its male counterpart. In some cases, they are even larger than the males, which itself is extremely uncommon among mammals. 

How Big Are Beaver Kits?

Baby beavers are called kits. There are usually two to four in one litter. They are born with the ability to swim, but typically don’t do anything until their first few weeks of life has passed.  Kits are tiny and easy prey for predators.  They weigh around 1 lb at birth. When kits become adults, their larger size is ideal in scaring off predators.

There are a few differences between the 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 two years old and start mating at three years old. Beavers mate during the winter months.  Eurasian beavers are pregnant for a period of 2 to 4 months, while American beavers are pregnant for about 3.5 months.

Do Beavers’ Teeth Grow Forever?

Beavers have massive teeth which grow forever. Their upper incisors range from 20 to 25mm, and their growth isn’t hindered at any point. That said, beavers don’t exhibit the best dental hygiene, and their teeth are usually orange in color. 

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

Beavers teeth curve backward, which makes it easier for them to do their jobs. The growth rate of their teeth is about 4 feet per year.  The teeth wear down with their gnawing of wood.

Beaver teeth

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

A study about the seasons and how it relates to incremental growth rates in beavers revealed that there is 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. 

It was found that the growth rate of the upper incisors differed 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 as much of a difference in growth between seasons. The top incisors may be used to estimate which season a particular fossilized beaver may have died.

What is the Largest Beaver on Record?

The heaviest and largest North American beaver ever recorded weighed 110 pounds or 50 kilograms. This beaver was from Wisconsin, and it was caught at Iron County.

If you have ever wondered if beavers can see in the dark, I have written an article about it here.

Were Beavers Even Bigger in the past?

Although they didn’t feature the classic flat tail, the giant beavers of the Ice Age 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 in size. 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 entire lifetime and weigh up to 60 or 70 lbs when there is enough food. In most cases, they live up to 24 to 25 years in the wild. The lifespan is reduced by a few years when they are held in captivity. 

Beaver trees
Beavers can gnaw through in a few minutes

Being semi-aquatic animals, beavers require a proper diet to survive properly.  Due to this reason, they are extensively found along 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 the marshy zones. Over the last fifty years, the number of beavers have increased in the zones in proximity to lakes, swamps, and woods.

Are North American Beavers Larger Than European Beavers?

The size of North American beavers and Eurasian (European) beavers are similar, with the European ones being just a bit larger.  Beavers adhere to a  zoological principle known as Bergmann’s Rule, which says that mammals living in colder locations are bulkier than those in warmer locations. 

The principle is named after its founder, Carl Bergmann, a 19th-century German biologist. It also explains how birds and adapted to emit body heat they live.  This  is  evidenced  by  the  fact  that  North American beavers  are larger, weighing approximately 45 lb. The total length of an adult North American beaver is 29–35 in with the tail adding an extra 7.9–13.8 in.

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

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

The longer shins allows them more flexibility and range when moving on their two feet, which has the knock-on effect of making it easier for them to utilize their two 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 species of beaver.

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 several factors, such as weather, pond location, age, and whether or not the colony had young.

During winter, both adult and baby beavers reduce in tail size and body mass, particularly those living in colonies who have young.  Beavers grow more during the summer, and their tails grow larger too.  There was no noted difference in these changes concerning gender.  Growth changes also differed between colonies.

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 especially useful when the species are on land. As beavers stand with their two hind legs for gnawing along tree trunks and branches, this tail acts as an added leg, allowing the rodent 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.

Another major highlight of this tail is that the beaver slaps their tail on the water every time they are looking to warn their friends about an impending danger. Their tails also assist them while swimming.

Beaver tail

However, while the tails of beavers stand as an excellent tool, there’s a common misconception regarding their use. According to the Washington Department of Fish and Wildlife, the tails of these species aren’t used for plastering mud on the 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?

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

They are also capable of slowing down their heartbeat as they are swimming in the water. This enables them to save a significant amount of energy and oxygen.  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.

After the air enters the trachea, this then  reaches the two bronchi. The bronchi then separate the air in the lungs, making way for the exchange of gas.  Every cell in a beaver’s body needs oxygen. 

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

How Big are Beavers’ Footprints?

Beaver print
Beaver print

Beavers have larger webbed rear feet and smaller, front feet that 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.  Both rear and front feet have five digits each.

How Big Are Beaver Lodges?

Beaver homes are called lodges.  They build these lodges from mud, sticks, grass, and moss. There are two types of beaver lodges.  The first is is a dome-shaped lodge, the other is a more straightforward den on the bank.  The tyope of lodge beavers build, depend on the water speed and water levels. 

Simple bank dens are built-in fast-moving water, while the domed lodges are built in slow-moving water. Beaver lodges have underwater entry points to these structures. 

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

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

Beaver dam

How Big are Beaver Dams?

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 a tree within a few minutes.

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

How to Watch Beavers?

Now that you have learned so many details 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 be able to enjoy a better experience watching them as they interact with each other and the other surrounding wildlife.

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 to other drivers by putting on your hazard lights. Make sure 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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Conclusion

Beavers are huge rodents with special adaptations such as thick fur, a large flat tail and webbed feet that enable them to build their famous dams, gnaw down trees and build their intricate and clever homes. 

Beaver dams change the natural landscape considerably, and this has many positive effects that help other creatures living in the same ecosystem.  Beavers have made their mark in popular culture, so much so that well-known idioms such as “eager beaver” and “busy as a beaver” reflect their excellent work ethic and enthusiasm.

If you or someone you know loves beavers then have a look at my favorite beaver gifts on Amazon.

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 Mammals.

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