Building It Back – Beaver Reintroductions Across the World

Katarina Samurović


The beaver is one of the iconic mammals of the Northern hemisphere.

Beavers are the largest rodents in North America and Eurasia, and the second-largest rodents in the world – after the capybara. They are well-known for their semi-aquatic lifestyle, cute disposition, and, perhaps above all, the ability to build dams across their habitats.

However, historically, beavers have also been known for their “produce.” People on both sides of the Atlantic hunted and trapped the beavers continuously. The goal of the hunt was  predominantly the beaver fur, but also meat and castoreum – a secretion from the beaver’s castor sacs that had various uses, from making perfumes to food additives. The demand led to a near-extermination of beavers across their entire range. 

Fortunately, it took something as simple as a hunting ban prevent the extinction. Today, both beaver species – the Eurasian Beaver (Castor fiber) and the North American Beaver (Castor canadiensis) have the LC (Least Concern) status on the IUCN Red List, meaning they are safe from becoming extinct. 

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Still, their numbers are much below what they used to be. In North America, at the end of 20th century the beaver population rebounded to 6–12 million; however, the original population was estimated to 60–400 million animals – meaning that today’s beaver population is just a fraction of what it used to be.

The beaver faces the camera. Its tail extends to the right and is cocked on its side, making the paddle-shape more visible.
A beaver rests in the water near Beaver Marsh’s snow-covered banks. Photo: NPS, public domain, Cuyahoga Valley National Park, Ohio.

The extent of the hunt also caused beavers to become thoroughly wiped out from many areas – and are now unable to repopulate them naturally.

That is precisely where conservation projects come into the picture. 

Since the 1920s, beavers have been artificially re-introduced to many habitats across their former range.

Let’s have a look at some interesting beaver reintroduction success stories.

Reintroduction of Beavers in California

The historical Californian beaver population was unfortunate enough to become extinct in the early 19th century, probably during the California fur rush – long before the creation of precise scientific records from the area. That is why the original conclusions on the historical range of Californian beavers were very likely untrue.

By the beginning of the 20th century, researchers of the day concluded that the presence of beavers in California was sporadic at best.

Adult and juvenile beaver near Windrose, Oregon.
Adult and juvenile beaver near Windrose, Oregon. Photo: Erin Poor, U.S. Geological Survey. Public domain.

However, the fact is that these nature historians had very limited access to records and physical evidence. Today, their findings are increasingly being questioned.

The new body of research reveals that California likely had a robust native beaver population – and that the beavers were the main driving force behind the creation of now-gone Californian wetlands in places such as the San Joaquin Valley.

However, as influenced by the previous narrative on their natural history, the beavers in California were – and sometimes still are – perceived as non-native pest species. As a consequence, their dams were often torn down by wildlife managers.

A beaver dam across a river.
A beaver dam. Photo: John J. Mosesso, USGS. Public domain.

Today, the Californian Fish and Wildlife Service acknowledges that beavers are native to California and proposes a number of ways to avoid and mitigate any beaver-human conflict.

One of the controversial points of the Californian beaver natural history was the Sierra Nevada mountains – a locality considered to be at an altitude not suitable for this rodent to thrive. Still, the reintroduction of the native beaver population tells a different story. 

The reintroduction began as soon as 1940, mainly to prevent ecosystem degradation. The Californian golden beaver individuals (Castor canadensis subauratus) were taken from Snelling and Waterford, both in low elevations (256 ft and 51 ft, respectively), and relocated at the Mather Station, west of Yosemite National Park, at an elevation of 5,062 ft. 

Best beaver house noted in region about snelling (horizontal).
A beaver lodge near Snelling, California. Photo: Joseph Dixon, December 18, 1922. NPS archives.

Seventy years later, this beaver population still thrives. The lowland beavers adapted to the heights of Sierra with no known issues.

Also, nine individuals of North American beaver were reintroduced from Idaho to the Tahoe Basin as well in the period between 1934 and 1949. By 1987, the descendants of these beavers on the upper and lower Truckee River had reached a density of 0.72 colonies (3.5 beavers) per kilometer.

Reintroduction of Beavers in Finland 

Finland makes for a curious case of beaver reintroduction. First of all, it happened quite early – the native Eurasian beaver was hunted to extinction in 1868, and the first beavers were reintroduced in 1935.

However, the choice of new beaver stock wasn’t the luckiest. The first batch was a regular one, made up of 17 individuals of Eurasian Beavers.

However, the second one, released two years later, consisted of seven North American beavers, sourced from New York.

Beaver lodge in North Karelia wilderness of Finland.
Beaver lodge in North Karelia wilderness of Finland. Photo: Janos /

Consequently, today, the North American beaver is five times more numerous in Finland than the native Eurasian beaver – 10,000 vs. only 2,000 individuals, probably due to the slightly larger fertility of the American species. It has also spread to neighboring Russia and is regarded as a non-native invasive species in both countries. 

Why would Finland introduce a non-native beaver species to its territory? The answer may surprise you. 

Back in 1935, the fact that there are two beaver species in the world was virtually unknown

This oversight was possible because the two species are extremely physically similar, at least on the outside. However, only in 1973, it was discovered that beavers from North America and Europe are vastly genetically different: While the Eurasian beaver has 48 chromosomes, its North American cousin has only 40. In comparison, the difference in chromosome numbers between humans and chimpanzees is only 2. 

As with other non-native beaver populations across the world, the governments of Finland and Russia are monitoring the accidental C. canadiensis population and considering possible eradication strategies.

Reintroduction of Beavers in Scotland

The British Isles (specifically, England, Wales, and Scotland, because beaver populations in Ireland were never known) are possibly the first place where beavers went extinct – way back in the 16th century

The Scottish Beaver Trial project was the first one that was set to change that after 400 years of the little builder’s absence.

The first release of beavers into the British wild with no fencing ran from 2009 to 2014, and is significant for another reason – it was the first-ever formal reintroduction of a native mammal species in Britain.

The Trial resulted in an established novel population of beavers in Argyll. 

A European beaver swimming in a river in Scotland.
European Beaver (Castor fiber), near Blairgowrie.  © Copyright Mike Pennington and licensed for reuse under this Creative Commons Licence

However, another unnamed beaver group has emerged in the Tay and Forth catchments in the country’s east. It was created from escapees and unauthorized releases. 

After a successful trial and a five-year study on how beavers enhance the natural environment, in 2016, the Scottish Government decided that beavers should remain in Scotland and be assigned a protected species status. 

Reintroduction of Beavers in The Balkans

In the Balkans, Europe’s southeastern peninsula, beavers became extinct only in the second half of the 20th century. After being gone for some 50 years, the Eurasian beaver was first reintroduced to Croatia (1996-1998), followed by Serbia (2004) and Bosnia (2005). The individuals for these projects were sourced from Bavaria, Germany, where beavers were re-introduced during the 1960s and 70s, resulting in a now-stable population.

Despite modest funding and oftentimes tricky situation with habitat protection, the Balkan beaver reintroduction looks like a success. Beaver families keep spreading their range, mainly along the Sava river and its tributaries. The environmental impact of the newly established populations is being tracked.

A statute of a beaver with a chewed and down tree sitting on the grass.
Beaver statue at Special Nature Reserve Zasavica, the first site of reintroduction in Serbia. Photo: © Aleksandar Djordjevic, used with permission.

In the Special Nature Reserve Zasavica, Serbia, the beaver even got its own statue. It was carved out of a rock from a Roman empire-aged archaeological site – symbolically, a time when beavers were still abundant in Europe.

Why are we reintroducing beavers?

So, is it necessary to reintroduce beavers throughout their entire former range, and why?

Although beavers do not play such a major role in the food network, they have an essential role in modifying the ecosystems they inhabit, creating numerous unique microhabitats through their activities. That is what makes beavers keystone species

Beaver dams modify the water flow in their chosen stream or river site and create ponds and wetlands. This beaver-led diversification of aquatic habitats benefits many creatures – and it is no wonder that areas inhabited by beavers have greater overall biodiversity than similar areas with no beavers.

A tree lays on its side with its pointy end resting on the pointy stump. The wood is pale where it has been chewed.
Recent beaver activity is indicated by chewed trees with pencil-tip cut markings. Photo: NPS, public domain, Cuyahoga Valley National Park, Ohio.

Also, beavers collect branches and even knock down entire young trees to get their building material. While the last point may seem at odds with what we consider forest conservation, surprisingly, the beaver activity adds to the forest habitat diversity.

Beaver ponds and pond edges, forest stops, the abundance of coppice – all of these special, beaver-created habitats foster specific living communities, ranging from invertebrates to large birds.

Another example of how beavers help protect forests is not so obvious. In times of climate change, wildfires have become a major issue in all fire-prone parts of the world.

By “engineering” specific riparian habitats, beavers create fire-proof forest patches. Emily Fairfax, an assistant professor at the California State University Channel Islands, says that burning areas where beavers built their dams is “like trying to light a big old soggy sponge on fire.

Beavers and salmonids

For a long time – and until embarrassingly recently – beavers were considered pests that cause flooding and impair the passage of trout and salmon, lessening their breeding success. That was the theory, at least.

A beaver sits on the snowy bank of the river chewing on vegetation that it holds in its front feet.
Beaver, Yellowstone River. Photo: Neal Herbert, NPS, public domain.

However, the actual studies have shown that the presence of beavers and their constructions positively influence salmonid spawning in general,  increasing the number of fish, their size – or both. 

In fact, for nearly two decades, the research evidence shows that salmonids may benefit from beaver ponds – and that there may be a link between the decline of beaver and salmon populations.

For example, beaver dams provide slow-moving pools of water that provide habitat for vulnerable coho salmon and other species.

On the other hand, a study conducted in Arizona shows that beaver activity has a beneficial influence on non-native fish population, possibly giving them an advantage in competition with native fish. The findings suggest that beaver dam influence cannot be viewed in black-and-white. Each case of fish conservation involving beaver activity should be treated separately. 

(To Build a) Conclusion

For such an iconic animal species, our historic lack of real knowledge on beavers is almost embarrassing. 

Until half of century ago, we didn’t know there were two species of beavers. We hunted and trapped most of them down to extinction before we could study them, and then retroactively guessed their natural range. 

Two beavers swimming in a lake.
North American beaver (Castor canadensis), Acadia National Park, 2014. Photo: NPS, public domain.

Although we have commonly called them “ecosystem engineers,” it turned out that we had idea just how important they are for supporting habitat diversity and biodiversity in general – and that many of our assumptions about their “pest” traits were unfounded.

Luckily, conservation efforts are now allowing us to watch in real-time how beavers modify our river lines and forests to create precious microhabitats that we have nearly banished. 

Let’s hope that beaver reintroduction projects will continue to produce such interesting results, bringing back not just the beavers, but all those life forms that have depended on them as well.


The Studies:

Cavrić, K. (2016) Populacija europskoga dabra (Castor fiber L.) u Hrvatskoj (The European Beaver Population in Croatia). Master thesis. Josip Juraj Strossmayer University of Osijek, Faculty of agriculture

Fairfax, E., Whittle, A. (2020) Smokey the Beaver: beaver-dammed riparian corridors stay green during wildfire throughout the western United States. Ecological Applications, 30(8), 2020, e02225

Gibson, P.P, Olden, J.D., O’Neill, W.O. (2014) Beaver dams shift desert fish assemblages toward dominance by non-native species (Verde River, Arizona, USA). Ecology of Freshwater Fish 2014.

Kunovac, S (2015) Ten Years After Beaver Reintroduction In Bosnia And Herzegovina. Naše Šume/Our Forests UDK 639.112:599.322.3(497.6)S

Naiman. R.J., et al (1988) Alteration Of North American Stream By Beaver. BioScience Vol. 38. No 11

Parker, H., Nummi, P., Hartman, G. & Rosell, F. (2012). Should (and can) the invasive North American beaver Castor canadensis be eradicated from Eurasia? — Wildlife Biology 18: 354–365

Pollock, M.M., et al. (2004) The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA, North American Journal of Fisheries Management, 24:3, 749-760, DOI: 10.1577/M03-156.1

Vehkaoja, M., Nummi, P., Parker, H., Hartman, G. & Rosell, F. 2013. Amerikanmajava Castor canadensis Suomessa ja Euroopassa: pohdintoja vaikutuksista ja mahdollisesta hävittämisestä. – Suomen Riista 59: 52–61.


Beavers create fire-resistant forest patches. Joshua Rapp Learn. The Wildlife Society. 9 October 2020.

Beaver in The Sierra Nevada, Wikipedia, The Free Encyclopedia. Retrieved 30 November 2021

Beavers Used to Be Almost Everywhere in California. Alison Hawkes. Bay Nature. 19 June 2014.

Keep Me Wild: Beaver, California Department of Fish and Wildlife,

Reintroduction of Beaver in Serbia – Zasavica 2004


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About the author
Katarina Samurović
Katarina Samurović is an environmental analyst and a freelance science writer. She has a special interest in biodiversity, ecoclimatology, biogeography, trees, and insects.