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Recognizing their role in maintaining healthy watersheds, “beaver believers” work to rehab the rodent’s reputation

Eager: The Surprising, Secret Life of Beavers and Why They Matter

Ben Goldfarb
Chelsea Green
302 pp.
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Why should we care about beavers? Consider all they do. Beavers convert vegetation to marsh to wetland and back again. They facilitate water storage in ponds and recharge groundwater. Ponds and meadows sculpted by beavers concentrate nutrients such as nitrogen and phosphorus. Not only does this create fertile ground, it helps filter agricultural runoff. Beaver-dammed landscapes create habitats for other species, and their complexes can serve as wildfire breaks.

Researchers have calculated that between 15 million and 250 million beaver ponds once covered North America. A booming 19th-century trade in beaver pelts, along with a loss of habitat due to settlement, almost wiped them out. The landscape they helped to shape was a watery quagmire—and a classic example of shifting baselines. Because we didn’t notice the initial profusion of beavers in the wild, we think current populations are normal.
Beaver populations recovered through the 1920s and 1930s, but never to their original numbers. Eager, by Ben Goldfarb, examines how they’re getting along today.

Beavers still face obstacles when we attempt to reintroduce them into ecosystems in which they once flourished. Predators can eat a beaver for lunch, while cattle grazing removes vegetation and can alter a stream’s configuration in such a way that it can no longer support beaver populations.

Even wild ungulates can be a detriment to beavers. Goldfarb describes how the reintroduction of wolves into Yellowstone National Park led to the recovery of vegetation and rerouting of stream channels, which some researchers maintain was the result of an increase in the availability of streamside willows and alder for beavers. But one of the main barriers to beaver reintroduction is policy, especially in states such as New Mexico, where legislators fear beaver activity will harm the cattle industry.


Some researchers believe that beavers were critical to promoting ecosystem recovery in Yellowstone.

Eager also highlights the problems of preconceived assumptions about beavers and beaver management. A common supposition among fish ecologists, for example, is that beavers are bad for salmon because their dams prevent the fish from swimming upstream. However, Goldfarb cites a comprehensive review of 108 papers that showed that beavers benefit fish populations more often than they cause negative consequences. A more egregious error occurred in California in 1937, when ecologist Joseph Grinnell declared that beavers had never inhabited large portions of the state. Although this was untrue, it went unchallenged and affected beaver recovery and ecosystem management across the state until it was disproven in 2012.

With drought in the southwest United States, there’s talk of building new dams. Beavers could do that for us—and create a fully functioning ecosystem while they’re at it. Goldfarb visits a property in Nevada, where a local rancher was able to extend his water availability by two months by allowing beavers to colonize one of his watersheds.

Later in the book, Goldfarb suggests that we could combine the heavy-duty approach of river restoration (such as use of backhoes and rip rap) with the work of beavers by installing beaver dam analogs (BDAs): two posts hammered into the ground with twigs woven between them (Science, 8 June, p. 1058). The BDAs, he argues, would speed up ecological recovery by encouraging beavers to colonize designated watersheds.

Goldfarb speaks largely with “beaver believers”—individuals who try to help humans and beavers coexist by mitigating the impact of beavers on the built landscape and by reintroducing them into stream systems that they can potentially restore. He lets his interviewees tell the majority of the story, recalling, for example, Councilman Mark Ross’s interaction with a local businessman during a tense meeting of pro- and anti-beaver groups in Martinez, California (“‘This seventy-year-old guy is about to hit me! …Do I hit back against a senior citizen or not?’”) and Yellowstone scientist Dan Kotter’s description of the effects of bison grazing on riparian vegetation (“It’s…like Jabba the Hutt eating a piece of pizza.”)

Goldfarb ends the book with a trip to the United Kingdom, where beavers haven’t been seen since the 17th (Scotland) and late 18th (England) centuries. Here, reintroduced beavers are a huge tourist draw, and beaver dams reduce the impacts of flooding—a big problem in the UK—although many farmers aren’t convinced. As Goldfarb writes, “Everyone shares a goal; no one agrees on strategy.”

One thing Eager was missing was a visit to Canada. The beaver is the country’s national animal and graces its nickel coin. Canada has acres of landscape shaped by beavers, and Goldfarb cites a number of Canadian studies, but a firsthand experience would surely have enriched his otherwise excellent story.

About the author

The reviewer is a freelance science writer and editor and cofounder of Science Borealis, Canada’s science blog aggregator.