A New Neighbor Moves In

By Elizabeth Farnsworth Gazette Contributing Writer

I have this really troublesome neighbor. First, right after he moves in, he clears most of the trees on his land. Then he dams up the stream that runs along our shared property boundary to create a pond, with no permit from the Conservation Commission. Sure enough, the water table in my basement is rising and, during heavy rains, our street floods! I guess I shouldn’t complain so libelously in a newspaper article. But I don’t have to worry – he can’t read English, or even speak Human. He’s a beaver.

Yes, beavers (Castor canadensis) can cause short-term problems for homeowners when they start to alter the hydrology of the neighborhoods we have built near their wetland habitats. They definitely live up to their reputation as busy, eager ecosystem engineers. They defy even our most high-tech attempts to knock down their dams or install “beaver-deceivers” to circumvent them. Beyond being befuddled by their landscape modifications, perhaps we are a little intimidated at how effective their almost- human ceaseless tinkering can be. But let’s take a closer look at this amazing mammal and the ways it has shaped human history and continues to help boost the biodiversity of all sorts of other creatures.

Weighing in at 30 to 80 pounds, beavers are North America’s largest rodents. They provided pelts, medicine and food to Native American populations long before colonists settled the Pioneer Valley. Colonial commerce ramped up considerably when beaver pelts—which are warm and rich in oils and ingredients for perfumes—became a prized export commodity for shipping to Europe; many early New England outposts were settled near areas where beavers could be profitably harvested. This trade decimated beaver populations during the 17th and 18th centuries, extirpating them completely from Massachusetts and Connecticut. In the decades since the 1950s, when beavers were reintroduced, their populations have rebounded, particularly since forested habitats have expanded and their natural predators, especially gray wolves, have declined. The beaver is another testament to the resilience of species when given a chance to recover.

As you read this article over coffee, beavers are out there munching a breakfast of birch, alder, ash trees and willows, though the bark and twigs of just about any tree species will do in a pinch, and water lilies and pondweeds supplement the menu. Two to five kits, born in late May after about 100 days’ gestation, are scrambling about the lodge, learning which vegetation is especially tasty; they’ll stay in the family unit for two years. Two-year-olds, newly kicked out of the colony, are scoping out new territories and lifelong mates about this time of year. Throughout the day, adults will be assiduously adding mud and twigs to shore up dams and the lodge. Beavers are best observed at dusk; I once watched an exuberant kit disrupt a romantic pas de deux between mother and father at Paradise Pond at Smith College during a picnic dinner in July.

But what good do beavers do? Studies by Robert McMaster of Holyoke Community College demonstrate that beavers increase the diversity of wetland plant species in the ponds they create. A colony will persist for several years, creating an essentially aquatic habitat rich with submersed and shoreline plants.


Foraging beavers typically create a buffer of 150 feet around a waterway. This buffer area provides habitat and travel corridors for turtles, frogs and salamanders and breeding areas for crayfish. The still waters of beaver ponds support many insects—such as mayflies and dragonflies—that are important to predators such as bats and birds. Although beaver dams can impede migration of some fish such as salmon, juveniles of other fish species benefit from the shelter of coarse woody debris and zooplankton thriving in the highly productive waters. Wetland edges also attract many mammals, including moose, deer and otters.

Beaver colonies eventually move on, allowing the pond to transition to a wetland, then to a meadow, and eventually to a shrubland or forest as the dam decays and the water subsides. From a bird’s-eye view, many streams appear as strings of pearls, reflecting the variety of successional habitats created as beavers abandon one site and set up house downstream.

Such shrublands become important refuges for birds that prefer scrubby habitats with complex vegetation. Richard Chandler and colleagues at the University of Massachusetts Amherst found that several rare or declining bird species, including the chestnut-sided warbler and sharp-shinned hawk, are abundant in large beaver meadows in western Massachusetts. And birds aren’t the only beings with wings that benefit from beavers. Studies in Finland indicate that several species of bats are more abundant in areas with large beaver impoundments, possibly because these ponds are rich sources of insect prey. Our New England bats need all the help they can get right now as they fight off deadly white-nose syndrome; maybe beavers can help them in the struggle. The beaver is what ecologists call an “umbrella” species—protect the beaver and you’ll conserve a lot of other associated critters.

So although I might sometimes find my new furry neighbor a little annoying, I realize he’s utterly fascinating. And he’s here to stay.

Elizabeth Farnsworth is Senior Research Ecologist at the New England Wild Flower Society, teacher, and scientific illustrator who lives by beaver-rich Lawrence Brook in Royalston. More information about living with beavers in Massachusetts, can be found at the Department of Fisheries and Wildlife.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 845 West Street, Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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