Controversial Castor, or, the Re-Introduction of Beavers

North American beaver. Photo credit: Jamin Warren

As discussed in my last post on passenger pigeons, sometimes conserving a species means re-introducing it to its environment where it had previously been extirpated. While passenger pigeons are an extreme example, local extinctions occur quite frequently. For example, if you’re a New Hampshire native like me, you may not realize that turkeys and beavers were once locally extinct here. That is, until they were reintroduced quite recently by human intervention (turkeys in 1975, and beavers in 1930). Now turkeys and beavers are all over the place!

A lot of thought goes into re-introducing species, and re-introduction ecology can be thought of as a discipline of its own. Conservationists need to consider the likelihood of success, as well as potential pit-falls. A re-introduction will fail if the drivers of the local extinction haven’t been resolved. For example, if hunting was the primary cause of local extinction, hunting regulations need to be created and enforced. Habitat loss is a harder problem to solve, but sometimes habitat is restored on its own- like when agriculture became less prevalent in New England and much of the land reverted back to forest.

Other questions can be raised when re-introducing a species, like has another animal filled its ecological niche? Is there public support for the reintroduction? What will change with the new population of animals? Are there dangers to humans and property?

The beaver is a great example. The two species of rodent, Castor canadensis and Castor fiber, were aggressively hunted for their fur and glands, leading to many local extinctions, but not complete extinction. It has made a great comeback in some places like New Hampshire.

North American beavers, by John J. Audubon. 

Beavers are an important part of the landscape because they create beaver ponds, which are habitat for lots of fish, plants, and other organisms. The series of ponds and dams along a stream also help to slow the water down and also decrease the potential for flooding. By gnawing trees down, they also create early successional habitat.

I think beavers are really neat animals- they are great swimmers but terrible runners, they have webbed hind feet, they use their tails to slap the water to warn other beavers of danger, and they never stop growing! Seriously, adult beavers can be anywhere between 40 and 90 pounds!

A heron utilizing a beaver pond. Photo credit: Peter Warren

So why would their reintroduction be controversial? Well, if you’ve inherited land from your parents or grandparents that was pasture or cropland in their time, you might be annoyed if beavers move in and turn it into a wetland. However, it’s likely that historically, beavers were always moving in and out of that area in cycles- once they cut all of the wood down and run out of things to eat, they will abandon a pond, but other beavers will return when it becomes suitable again. This didn’t happen in your grandparents’ time because of the local extinction of beavers, so it might seem like a new phenomenon.

In England, beavers have been spotted for the first time since the 12th century. It’s not clear how they got there, as it was not a purposeful reintroduction, but they may have been released by humans or migrated. A plan is in progress to re-introduce beavers to another location in England. What’s striking to me is the rather modest amount of enthusiasm, and even negativity, about the arrival of the new neighbors. Beavers have a huge impact on the landscape (second only to humans, according to NatGeo), so it’s understandable that people are worried about the effects to their property. The hope is that overall, the improvements to biodiversity, water quality, and flooding will outweigh the added complications the beavers bring.

Reintroductions are not necessarily limited to animals! If you’re hungry for more knowledge, look into the American Chestnut!