Few mammals, aside from humans, can create large-scale changes to their surroundings to suit their habitat needs. One such animal, commonly found at Bernheim Forest, is the North American Beaver (Castor canadensis). Known as “ecosystem engineers,” these large rodents build dams in streams and rivers, creating ponds or wetlands by backing up the water. Beavers use their strong, iron-rich teeth, which have an orange hue, to fell trees. They then pile logs, branches, sticks, mud, rocks, and vegetation to construct their dams. They often build dome-shaped lodges in the deepest part of the pond or wetland. Some beavers may choose to excavate burrows along the banks of ponds or rivers to serve as their living quarters.
Beavers are semi-aquatic mammals. While they forage on land, they prefer the safety of water, which protects them from predators like coyotes, bobcats, black bears, river otters, eagles, and hawks. They can remain submerged for up to 15 minutes, aided by clear membranes covering their eyes like goggles, and by ears and nostrils that close to prevent water from entering. This ability allows beavers to dig multiple underwater entrances to their lodges. Remarkably tidy, beavers often create a “mud room” on the lower level of their lodge, connected to the above-water living area by a sloped tunnel.
Beavers instinctively stop flowing water, creating wetlands through their dam-building, even when raised in captivity. Although damming is part of their DNA, beavers are also highly family-oriented. They refine their dam-building skills by observing their parents and older siblings, as daily lessons are part of family life. Beavers live in extended family units, known as colonies, where bonded pairs typically copulate in mid-winter. A single litter of 2–4 kits is born each year, with both parents co-raising them for up to two years before they establish their own territories. During this time, kits also learn from their siblings from the previous year’s litter.
While beaver activity, such as flooding streams, may sometimes cause problems for humans and infrastructure, it’s important to view these wetlands from a historical and ecological perspective. During the fur trade (mid-17th to mid-19th centuries), beavers were nearly wiped out in North America due to European demand for their pelts. Prior to this, beaver populations were much higher, and wetlands they created remained undisturbed without the pressures of modern development and agriculture.
Today, we live in a dramatically altered landscape. Habitat loss and urban sprawl have led to a significant decline in wetlands. A 2024 report from the U.S. Fish and Wildlife Service reveals that up to half of all wetlands in the lower 48 states have been lost since European settlement in the late 1700s. Wetland loss has accelerated by 50% since 2009, posing a serious issue. Wetlands are essential for flood control and support hundreds of species, acting like sponges during storms by containing water that would otherwise flood infrastructure and cause damage to human and animal lives.
Next time you hike the Forest Giants Trail, as you pass Lake Nevin and the Olmsted ponds, keep an eye out for signs of North America’s most prolific ecosystem engineers.
For more information about beavers and their history at Bernheim Forest, check out Bernheim’s Director of Conservation’s blog post, Beavers – Ecosystem Engineers, originally published in the Summer 2024 issue of the Forest Echo, Volume 33, No. 3.
U.S. Fish and Wildlife Service. (2024, March). Continued decline of wetlands documented in new U.S. Fish and Wildlife Service report. https://www.fws.gov/press-release/2024-03/continued-decline-wetlands-documented-new-us-fish-and-wildlife-service-report
