Canadian Invaders!

Leanne Grieves
15 November 2018

Above: A beaver looks up from the water. Image © Jillian Cooper,

If you live in Canada, you’ll recognize the beaver from our nickel coin. You have probably also seen the large, mud-and-stick lodges and sturdy dams that beavers build.  Beavers are an important part of Canadian history. During the fur trade of the 1600s and early 1700s, they were trapped and hunted for their valuable pelts. At the height of the fur trade, around 200, 000 beavers were killed in Canada each year!

Did you know? The beaver was officially recognized as an emblem of Canada on March 24, 1975.

By the 1900s, beavers were scarce across North America. In the 1930s, a beaver conservation movement began. Because of this, people stopped trapping and hunting beavers for many years. Eventually, beaver populations grew back to a healthy level .

Did you know? The beaver conservation movement of the 1930s happened largely thanks to Grey Owl, a man who wrote passionately about Canadian wildlife. Some people call him one of Canada’s first conservationists.

Beavers (Castor canadensis) occur naturally throughout most of North America. In other words, they are a native species here. In 1946, 25 pairs of beavers were brought to the South American countries of Argentina and Chile. These countries hoped to encourage fur trade there, too. Today, that number has grown to 200, 000 beavers.

In Canada, beavers have natural predators. Wolves, coyotes and other large predators kill and eat beavers. This way, the number of beavers stays at a healthy level for the ecosystem.But the beavers in South America have no natural predators. Because of this, they were able to colonize peat bogs, grasslands and other environments.

In parts of South America, beavers have become an invasive species. Invasive species are species that cause harm in an area to which they are introduced. Unlike native species, invasive species do not naturally occur in that area.

What is so harmful about beavers?

Beavers use their strong, sharp incisors to cut down the trees they need to construct their dams and lodges. Because of this, they are destroying South American forests. North American tree species can often grow back after being cut down by beavers. But South American trees have no such coping mechanisms, and the trees do not grow back.

Did you know? The beaver is the second largest rodent in the world. Only the capybara of South America is bigger.

Beaver dams have also led to flooding in many areas. This can drown and kill old-growth trees in South America, many of which are over 150 years old. The beaver dams are also destroying peat bogs, which are a crucial part of the environment.

Many of these South American forests can only regenerate from seed banks lying dormant in the ground. When the areas next to beaver dams flood, the seeds drown and die. This means that the area of forest lost to beavers won’t recover.

The beaver dams have also disrupted trout migration. As well, beaver dams can create bogs. This means land animals must now navigate bogs in areas that used to be lush river deltas.

And the impacts are not just environmental. Beaver-related flooding has also destroyed roads and bridges, and contaminated drinking water. The invasive beavers have caused millions of dollars in damage!

What are the solutions?

The government of Chile has dedicated $7.8 million dollars to fight the massive destruction caused by North American beavers. In 2008, Chile and Argentina signed an agreement to get rid of beavers and restore the ecosystems affected by their invasion. In 2017, these governments announced a plan to cull over 100, 000 beavers over 10 years.

One option is to train hunters to quickly and humanely kill the beavers. Other methods include encouraging trapping and offering rewards for beaver hunting. For example, hunters could receive a bounty (a sum of money) on beaver tails.  These countries might also try to introduce beaver meat as a delicacy. This would encourage people to eat the meat from hunted beavers so that it would not go to waste.

Some animal rights groups oppose these methods. Instead, they are pushing for beavers to be trapped live and shipped back to Canada. But biologists in Chile argue this would take too much time and money. Also, once the beavers got back to Canada, they might need medical treatments and a period of quarantine. These two things would help ensure these beavers are healthy,and will not introduce new diseases to Canadian beaver populations.

Why is all this important?

Beavers in South America have caused a difficult and sensitive problem. Argentina and Chile need to protect their environments and economies from the beavers’ massive destruction.  But the governments’ solution of killing over 100, 000 animals is difficult for many people to accept.

We can learn important lessons from the introduction of North American beavers into South America. Before people move species from one place to another, they must first do some careful research to make sure these moves will not cause problems. People must always strive to balance the costs and benefits of their actions. As this example shows, correcting past mistakes can involve making very difficult decisions.

Learn more

About beavers
Hinterland Who’s Who by the Canadian Wildlife Federation

Canadian Wildlife Federation


Hinterland Who’s Who by the Canadian Wildlife Federation

Canadian Wildlife Federation

Official Symbols of Canada: Beavers
Government of Canada

South America’s Forests: A Canadian Beaver’s Buffet

Just in time for Trudeau’s visit, Argentina declares pitiless war of extermination on Canadian beaver (2017)
National Post

Beavers imported from Canada are threatening the primeval forests of Patagonia (2017)
LA Times

Canadian Beavers Are Destroying Patagonian Forests In Chile And Argentina
Huffington Post

Dam! Imported Canadian beavers are wreaking havoc in South America(2017)

Cantech Letter

Argentina plans to cull 100,000 beavers (2016)

Quarantine And Health Screening Protocols For Wildlife Prior To Translocation And Release Into The Wild (2000)
Canadian Wildlife Health Cooperative

Leanne Grieves

I was born and raised on the Canadian prairies in the province of Manitoba. As a child, I spent countless hours outdoors and exploring nature. In fact, I spend countless hours as an adult doing the same! In 2012, I earned my Bachelor of Science degree in biology from the University of Winnipeg, Manitoba. There, I gained my first research experience working with marsh-dwelling red-winged blackbirds. I moved to Hamilton Ontario and completed my Master of Science degree in biology at McMaster University. I spent about a year in total in Puerto Rico studying acoustic communication in a unique bird species, the smooth-billed ani. Currently, I am a 3rd year PhD candidate studying chemical communication, avian malaria, and mate choice in song sparrows at Western University in London Ontario. While I am interested in all sorts of creatures, I have been working with birds since 2008 and I wouldn’t have it any other way! (That photo is me catching my final song sparrow of the year.) I love sharing knowledge and encouraging others to appreciate nature, which is why I am thrilled to be a volunteer science writer with Let’s Talk Science.

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