Dam Beavers

Meet the Rodney Dangerfield of Alaskan wildlife

I’m casting for a dinner along a cut bank across from camp, evening colors reflected in the Nuna’s clear, purling current. The arctic stillness is broken by a wet, resounding crash, as if a rock had just been chucked from the sky. Though startled, I’m hardly surprised by my noisy company. Floating 30 feet away, a pair of unblinking eyes set in a wet, furry head regard me, radiating curiosity-tinged indignation. I can practically hear a Disneyfied, bucktooth nasal voice: Hey buddy, what the hell you doin’ in my yard? 

Another tail slap followed by a shallow dive, and the head pops up closer. I’m again fixed by that beady-eyed stare. I said, beat it! and with a final slap and a swirl, it vanishes. I track the bubble trail a few dozen yards down the bank to a mound of peeled, interlocked sticks cemented with mud, and in the adjoining eddy, a half-sunken raft of willow and alder branches: home and pantry to a family of one of Alaska’s most consequential but overlooked mammal species, Castor canadensis, the North American beaver. 

Beavers inhabit most of the state, from the rainforests of the Panhandle to the cold, arid valleys of the Brooks Range, and east to west across the state’s vast interior. The Arctic coastal plain and westernmost coastal areas, including many islands and most of the Alaska and Seward peninsulas, are without beavers—so far, anyhow. They’re arguably the most widespread of all Alaska’s bigger-than-a-breadbox mammals, and so numerous that there’s not even an official estimate of their statewide population. Considering that Maine, one-eighteenth the size of the Great Land, figures it has somewhere between 45 and 70 thousand beavers, a conservative guess for Alaska is somewhere around a half million, and possibly double that figure. 

And both their statewide range and numbers are swelling. University of Alaska ecologist Ken Tape and his colleagues have harnessed existing satellite imagery that demonstrates a dramatic increase in beaver ponds across arctic Alaska—from zero in the 1950s to many thousands today (impossible to get an exact count due to imagery gaps), and a continuing expansion into areas where beavers were unknown just a few years back. All this in response to warmer, longer summers that promote vegetation growth and a steadily expanding tree line across the state; and perhaps as well to a diminishing interest in trapping and hunting them for their once-prized pelts and rich, fatty meat.      

Besides being abundant and widespread, these super-sized rodents, averaging between 30 and 50 pounds and topping out near a hundred, are famed for their building skills and hardhat work ethic; the ol’ busy as a beaver trope is spot-on. They toil hard, long hours, generally in the dark of night and the crepuscular shoulder hours but are sometimes active in daylight as well. Not only do they gnaw down trees of all sizes—routinely 12 or more inches thick, and one report claims a credulity-straining five feet in diameter. They use limbs and sticks along with vegetation, armloads of mud and even sizeable rocks clutched to their chests to build and maintain remarkably efficient, sturdy dams and lodges—the former, to regulate water levels to suit their needs; the latter, year-round houses that may be used for generations and remain decades after the builders have moved on. In my travels across Alaska, from deep wilderness to suburban creeks and wetlands, I’ve seen dams ranging from a few bushels of sticks jammed in a culvert to edifices six feet high and a hundred yards long. A lodge may be a simple, stick-mounded burrow dug into a stream bank or a towering, conical fortress 20 feet in diameter. 

Not only are beavers industrious; scientists tell us their brain structures are indicative of considerable intelligence—which makes sense, considering that each dam and lodge is a unique engineering project, fashioned from locally available materials to fit a particular spot and set of conditions by a family group. There’s clearly more than instinct going on inside those stout, toothy skulls; in order to bring to fruition a dam, say, across a creek 20 feet wide, draining a tundra meadow, they need to be smart, adaptable, even imaginative—not to mention highly cooperative and hardworking—to pull it all off.  

Given that hundreds of thousands of folks from all over the planet are drawn to Alaska each year, hoping to view its incredible array of wildlife, you might expect beavers would be a huge draw. Accessible, numerous, displaying unique behaviors and building complex structures that are easily seen and interesting to interpret…you’d think Castor canadensis would be a major tourist attraction. 

Um, not so much. Sure, wildlife guides are happy to point out beaver handiwork or focus on a chance sighting, but it’s strictly a drive-by deal. For some reason, no one travels here yearning to see giant nocturnal rodents the way they do bears, moose, or whales. And most Alaskans are similarly indifferent unless their favorite trail or fishing stream is getting flooded. No matter that beavers are to Canadians what bald eagles are to us: a revered national symbol. They’re the Rodney Dangerfields of the Alaskan wildlife pantheon—they just don’t get no respect.    

But they should. Even more impressive than beavers’ edifices are the resulting changes they impose on the landscape. Though beavers are capable on dry ground and find much of their food and building materials ashore, they’re far more at home in the water. Once dammed, a slough, stream, or side channel may flood scores of acres, drowning trees and plant communities as the beavers purposefully shape habitat to suit their needs. The ponds and backwaters they create allow them to swim rather than walk to reach their chosen forage—willow, birch, balsam poplar, and alder branches, gnawed for their bark, along with various succulents—and to ferry huge amounts of them home to add to their food pile. Water (along with their impenetrable lodges fitted with underwater entrances) affords beavers safety from predators, chiefly wolves and bears. 

While beaver-induced flooding kills or excludes many species, it also swings open the gate for a host of others. Beavers are a living, gnawing exemplar of a keystone species—an organism whose presence and actions dramatically shape entire ecosystems. Wherever beavers abide, aquatic and water-loving shore plants thrive and increase in variety; birds, from ospreys to chickadees, find homes in standing deadwood; waterfowl feed and nest in dam-created backwaters. Young salmon and Dolly Varden grow plump on pond-dwelling insects as well; and an array of water-loving mammals from muskrats to moose benefit from beavers’ bioengineering. These buck-toothed ecological influencers don’t stop at the surface. In direct response to their work, the local water table rises, streams run clearer, soil loss declines, and the affected ground fixes more nitrogen and sequesters more carbon. All good with beavers then, right?  

Well, not so fast. Wherever dams are built, ponds form. The ground, underlain by permafrost, is warmed by the shallow, tannin-stained water—which leads to accelerated melting; a structural collapse of tundra known as thermokarst; ponds and lakes draining into thawed soil; and great gouts of methane being released into the atmosphere, which in turn hastens the already-scary rate of arctic and planetary warming. Ecologist Tape likens the rapidly expanding impact of beavers on the arctic landscape to wildfire: an irresistible, transformative force.

Pretty easy for us to shake our collective heads and commence finger-pointing. Those dam beavers. Look at the mess they’re making of things. Of course, blaming beavers and their industrial-scale doings for the burgeoning climate crisis is a whole lot like looking into a funhouse mirror. What other creature on the planet so relentlessly and cleverly shapes its entire environment by creating structures visible from space? 

Ahem. That’d be us.