Frances Backhouse’s natural history of the beaver, “Once They Were Hats,” chronicles the story of a species that has bounced back from the edge of extinction and proved able to coexist with humans.

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“Once They Were Hats: In Search of the Mighty Beaver”

by Frances Backhouse

ECW Press, 261 pp., $16.95

Reading natural history is fraught with a particular kind of peril. The typical progression from “here are amazing facts” to “there used to be [X] million of these majestic creatures, until humans wiped them out” is a disappointing road.

Frances Backhouse’s “Once They Were Hats: In Search of the Mighty Beaver” starts down that path, but the story ends in a slightly more upbeat place. The once ubiquitous beaver was nearly exterminated from North America in a shockingly narrow window of time — John James Audubon could not find one on his journey up the Missouri River in 1843, and he spent eight months looking — but now people make a living trapping them as “nuisances.”

How did we get here? Backhouse tells readers the story by tracing humans’ 15,000-year relationship with the beaver, from interdependence with humans chronicled in First Nation stories to present-day trapping.

Backhouse, a creative-nonfiction teacher who lives in Victoria, B.C., listens to Tlingit stories and songs in the Yukon, watches hat makers in Calgary, tromps the Skagit River delta, and hangs out at a fur-trading post in Saskatchewan. In one cringe-worthy chapter, she learns to skin a beaver. “I was glad to have had the opportunity — it was history made tangible, biology made intimate — but I knew I wasn’t cut out to be a trapper,” she writes.

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Scientists estimate that pre-European contact, North America was home to between 60 million and 400 million beavers. It took barely 400 years to trap them almost to extinction. By the early 1700s, Backhouse writes, Massachusetts was empty of beavers, and by 1850 the species was gone from six more states. It took the mountain men, trading independently of the big fur companies, just 15 years to eradicate them from much of the West.

But much more than fur was lost. The dam-building and waterway routing that beavers do make them a keystone species, or one whose effect on animals and plants is “disproportionately large, relative to its own abundance,” Backhouse writes.

In Washington, beaver dams built in the Skagit Delta increase habitat for young chinook salmon. Ponds with dams melt earlier than those without, creating fresh water for early-migrating birds. Beavers delay ponds’ freezing, too, by slapping icy patches with their tails or pulling at edges of the ice — a behavior that benefits late migrators.

The wetlands that beavers create make homes for ducks, herons, otters and plants and trees, which in turn attract elk and moose. Take a couple of beavers and a few generations, and a healthy ecosystem is born.

The species Castor canadensis has returned to all the states and provinces from where it was eradicated. Between 9.6 million and 50 million beavers now live in North America, including two named Jose E. Serrano and Justin Beaver, who live on the Bronx River.

Yet the habitat the beavers have returned to is not identical to the one they were driven from. This often puts them at odds with humans who’d like to keep their willow trees, their riparian landscaping and their functioning culverts. States and provinces rely on a range of methods, from humane trapping and relocating to more lethal means to “preserve” property.

We need to tread carefully here, Backhouse warns. “We need to cure our amnesia, rethink our relationship and acknowledge how much we stand to gain” from these newly returned neighbors.