By Todd Wilkinson
At dawn, Douglas Smith climbs into a small airplane and sets a course for the rugged interior of Yellowstone to track radio-collared wolves. By late afternoon, he's back on terra firma, this time perched on a six-foot dome made of mud and willow branches protruding from a freshly created wilderness pond.
Smith is not listening for howls now. He's waiting for the agitated tail slaps of Castor canadensis and trying to better understand the building blocks that make healthy ecosystems whole. In all of his years working as a federal wildlife biologist, including his current stint as chief wolf researcher in America's oldest national park, he has been intrigued most by the lives of "keystone species"—the pivotal creatures that profoundly affect the composition of plants and animals in the environment around them.
Considered functionally extinct at the beginning of the 20th century, beavers have made a dramatic comeback across the United States and Canada—good news for beavers as well as other species. The large industrious rodents create wetlands and marshy areas that provide habitat for hundreds of species.
 As much as Smith is captivated by wolves, he holds a special place in his heart for another keystone species—what he calls the "unassuming charismatic rodent" that inhabits the backwaters of public attention. Smith, of course, is referring to beavers, the largest native rodent in North America.
Legendary for their prowess at building dams and engineering wetlands, beavers are making a dramatic comeback across most of the United States and Canada. Today, the recovery of the beaver, though slow to reach some areas such as Rocky Mountain National Park, rates as one of the greatest conservation success stories. In dozens of national parks, from the glacier-coated valleys of Alaska to the mountains of Appalachia and southwest toward the Rio Grande, these shy aquatic mammals play a tremendous role in bolstering the diversity that makes parks important wildlife havens.
"The ecological role of beaver is tremendous," says Stewart Breck, a research biologist with Wildlife Services, an arm of the U.S. Department of Agriculture. "Beaver are credited with being able to alter the environment more than any other animal in North America, except for humans," adds Bruce Baker, a senior scientist with the U.S. Geological Survey in Fort Collins, Colorado.
Beavers, which often live in domed lodges, can grow as large as 65 pounds, breed in winter, and give birth to kits in the spring. They spend much of their lives in the water and are easy to trap. Notoriously slow moving, they waddle when on land, leaving them vulnerable to predators, including bears, wolves, coyotes, and cougars.
As recently as 300 years ago, scientists say 65 million beavers lived in North America, a conservative estimate in the eyes of some, who place the historical continent-wide peak at perhaps closer to five times that number. Regardless of the unofficial census figures used, beaver experts today agree on two points: these animals were once astoundingly abundant, setting the stage for the bounty of riparian wildlife European settlers found when they reached the continent; and the animals suffered radical depletion because of commercial fur trapping.
Beaver ponds and dams act as filters, capturing silt and other impurities. |
| Iconic American explorers Meriwether Lewis and William Clark had a hand in this exploitation. During their expedition across the country 200 years ago, Lewis and Clark established a series of fur trading posts, including Fort Union Trading Post National Historic Site in North Dakota, as a way for the United States to assert a larger geopolitical presence in global commerce. | |
Both the explorers had personal financial stakes in promoting the harvest of beavers. In fact, it was Lewis' declaration in a letter to President Thomas Jefferson that the upper Missouri River held more beavers than anywhere else on Earth that hastened a rush of fur trappers to the region. Within 40 years, beavers were virtually trapped out of the Rockies.
And by the beginning of the 20th century, just 100 years after the Lewis and Clark Expedition, beavers were functionally extinct in the United States.
"We are only now beginning to comprehend the effect that beaver had," Smith says. "Unfortunately, we're also still coping with the aftermath caused by removing these animals from most of the Lower 48 in an amazingly short amount of time."
The near-elimination of beavers led to a drying of wetlands and an expansion of meadows and forests to the detriment of marshy species. But beginning at the end of World War II, as a new age of ecological enlightenment emerged in the United States, hundreds of federal and state-sponsored beaver reintroduction efforts were carried out nationwide to enhance riparian habitat. Riparian zones—one of the richest and most diverse types of habitat—account for just 2 percent of landscapes in regions such as the American West, yet they provide 80 percent of wildlife with habitat at some point in their lives. Beavers, Smith says, are boons for species diversity.
 Consider the lesson from Voyageurs National Park in Minnesota, where Smith worked for 11 years. During the 1940s, aerial photos showed that less than 4 percent of the park was riparian habitat, but during the subsequent three decades when beaver numbers were allowed to grow, the amount of riparian acres quadrupled.
How can animals that can weigh up to 65 pounds affect epic positive change on a landscape level? "Beavers bring double rewards," Smith says. "They not only break up the landscape, but they affect the homogeneity of species by producing aquatic habitat that hundreds of related species cannot live without. Where you have beaver coming back, you'll often also see recovery of other species."
Despite beavers' reputation for causing flooding, their marshes actually help buffer adjacent landscapes against the effects of flash floods. Their network of channels, dams, and sloughs slows the water as it moves through a drainage, holds water in the landscape longer, insulates areas from drought, and recharges underground aquifers.
Among the biggest beneficiaries of beaver presence are moose, mink, and muskrat; numerous bird species including songbirds, wading birds, waterfowl, and raptors; as well as amphibians, reptiles, aquatic insects, and, of course, fish that thrive in slow-moving water, Baker says. Scientists also believe that beaver ponds may be crucial in aiding the recovery of imperiled trout, and along the West Coast some say the animals historically provided key habitat that aided large runs of coho salmon.
Beaver ponds and dams function as water filters that capture silt and pollutants, leaving water heading downstream cleaner. Despite beavers' reputation for causing flooding, their marshes help buffer adjacent landscapes against the effects of flash floods. Their network of channels, dams, and sloughs slows the water as it moves through a drainage, holds water in the landscape longer, insulates areas from drought, and recharges underground aquifers. Water that normally flushes through a river corridor in a single day will pass through beaver-inhabited environments in seven to ten days.
 Mark McKinstry, research scientist at the Wyoming Cooperative Fish and Wildlife Research Unit at the University of Wyoming in Laramie, has spearheaded a novel project in which 285 beavers were introduced into 14 Wyoming streams on public land and private ranches. The goals were to improve wildlife habitat, restore damaged streams, enhance natural water supplies for livestock, and combat aridity. The seven-year effort proved to be an overwhelming success. "Beaver deliver a huge bang for the buck. As a public investment, you'd be hard pressed to find an animal that delivers bigger returns," he says.
The fact that ranchers are learning to regard beavers as partners shows how societal attitudes have positively shifted, McKinstry says. It also demonstrates how national parks, in serving as reservoirs for less appreciated species, are ahead of their time. They continue to serve as important natural laboratories, delivering lessons that can be applied on a larger landscape level.
The Crunch on Beaver Food
Beavers feast on a variety of trees—birch, maple, oak, cherry, and balsam poplar-but if given a choice, they prefer aspen. Willow and cottonwood come in a distant second.
In a project in northern Minnesota, Douglas Smith studied beavers' feeding patterns in an attempt to explain why colonies occupy or abandon a particular pond. "If their chief food supply has, for whatever reason, been depleted, colonies may move on.
However, some colonies become so attached to a particular location that they choose to stay and forage on less desired trees than strike out for an alternative place to live," he says. Smith also found that beavers tend to be most active cutting down trees for their bark in the spring and fall, when leaves are not available to them. A ready supply of aspen bark has been linked to healthier and higher numbers of kits born to beaver mothers.
In Yellowstone and Rocky Mountain national parks, climatic factors and grazing pressure by elk have winnowed away the aspen forest, causing beavers, in recent years, to switch over to willow for nutrition. Smith identified 77 beaver colonies across Yellowstone's 3,600 square miles in 2002, and not a single one was living on aspen. Yellowstone, in fact, probably never supported dense beaver numbers.
In Colorado, Bruce Baker, a senior scientist with the U.S. Geological Survey in Fort Collins, Colorado, is studying how beavers compete with elk and moose for willow and what effect the combination of beaver tree cutting and intense elk grazing have on the willow forest.
When beavers chew through a willow trunk, it causes the tree to send out numerous suckers that result in more trees. The mud piles that beavers create along pond banks also are conducive to germination by willow seedlings.
On the other hand, intensive ungulate grazing, in which elk aggressively eat off both the buds of willow and the leaves that grow from new shoots, can depress willow regrowth, causing beavers to leave an area.
In its assessment of Rocky Mountain National Park, NPCA's State of the Parks® program stated that elk foraging was affecting willow stands, especially those found in the elk's winter range. One of the study's recommendations was to complete population studies of key vertebrate species to understand their abundance, distribution, critical habitat needs, and interactions within the park. | |
Of course, beavers can, and do, present challenges to humans. They topple trees in city parks and backyards, and their handiwork has flooded basements, roads, crops, and woodlands, causing millions of dollars in property damage each year, notes Breck. Only a few decades ago, the standard protocol for dealing with such enterprising beavers was dynamiting their dams and lodges, then trapping the animals. Today, Breck's Wildlife Services emphasizes nonlethal methods of management. Researchers with Wildlife Services have devised special materials to armor tree trunks, and they've discovered nontoxic chemicals that repel the animals.
For Smith, it's no coincidence that his study of beavers ultimately led him into wolf management. Not only are wolves and beavers bound together as predator and prey, but similarities abound. Both species shape the ecosystems they inhabit, exist in extended family units, and scent-mark their territories. Both have also developed unique ways of communicating. Where wolves howl to exchange information or sound an alarm of intruders, beavers slap their flat tails against water surfaces to put their kin on high alert.
In addition, both animals are classified as "cooperative breeders," a distinction that applies to only 2 percent of mammals in the animal kingdom. In simple parlance, cooperative breeding species are led by dominant males and females that remain monogamous until one of the mates dies.
"I've studied wolves and bears and birds and beetles, but beaver are one of the more fascinating creatures I've ever observed," adds Breck. "When you're out there watching them every night, your admiration for their work ethic soars. Far from being boring, I find them to be highly charismatic." |
It has taken us a long time to realize the damage caused by eliminating beavers. If past mistakes are to be remedied, long-term solutions must be found. "Public land managers and private property owners who embrace beaver as an ally may not see a whole lot of change in their lives," McKinstry says. "But if their grandkids are able to see the improvements these animals bring, then it's going to be a good thing."
Todd Wilkinson, a regular contributor to National Parks, last wrote about threats to America's native forests.
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