By RICK BORCHELT
Busy as a beaver is an accurate watchword for this industrious mammal, second only to the South American capybara among the world’s largest rodents. November and December are when beavers kick into overdrive, and our chances of seeing this mostly nocturnal creature during the day in local lakes and streams are pretty good.
Beavers (Castor canadensis) were all but ubiquitous in Maryland when European settlers arrived in the 16th century. It’s no great stretch to say that the Maryland landscape early settlers found was literally sculpted by beavers. The state’s streams were dotted with beaver ponds every half mile or so, strung like a necklace of pearls across the landscape.
Courtesy of National Park Service
Each pond was created by a family of beavers that built a dam to flood the area. Rich, diverse habitats evolved around these ponds — stands of willows and alder, and wet grasslands studded with orchids, irises and carnivorous plants. Beavers worked overtime to keep trees from invading the shallow waters and cattails and water lilies from choking the waterways; their activity in the ponds, the surrounding woods and wetlands was vital to organisms throughout the ecosystem. In this way, beavers are what we call a keystone species. Think of an arch made of stones; the keystone, at the top, holds all the stones in place. But pull that keystone, and the arch falls apart. The same thing’s true in nature; if you remove a keystone animal whose contributions are essential, like beavers, an entire ecosystem could fall apart.
By the late 1800s, though, beavers had been nearly wiped out east of the Mississippi as we turned their thick, brown waterproof pelts into fur coats and warm hats. As beavers disappeared, the ecosystems they created changed dramatically. A host of forest and wetland plants and animals that depended on beavers to manage their habitat, including the Baltimore checkerspot, our iconic state butterfly, became endangered — or were wiped out entirely. The loss of beaver dams also made streams more prone to catastrophic flooding during severe weather events.
Beavers are active all year long, and their diet changes with the seasons. In spring they eat fresh green buds on willows and other streamside trees and shrubs; as spring turns to summer, beavers turn to grass, water lily and cattail tubers, and leafy vegetation. Beavers store up fat under their warm coats and in paddle-shaped tails the size of dinner plates.
Even with this stored fat, they face challenges as winter rolls around. With fresh food disappearing, these aquatic engineers turn their skills from foraging to refrigeration.
The water in our lakes stays pretty cold from November to March, a perfect icebox in which beavers can store green branches with tasty buds, limbs with tender bark they can gnaw off, even entire small trees. Under the cover of darkness, beavers waddle out and gnaw down trees they can drag back to the lake. One adult beaver can fell 200 or more trees a year to feed the lodge’s stay-at-home offspring and their parents.
In the fall, the woods around beaver lodges are studded with the peculiar, pyramidal short stumps the beavers leave behind as they gnaw down trees and ferry them off to the underwater refrigerator. There, the lodgers can dine at their leisure, even if the lake is covered with ice.
Beavers are superbly adapted for this forestry work; they have huge upper and lower front teeth that are laced with iron, giving them added strength and a bright, rusty-orange cast. Those teeth can take out an eight-foot sapling in five minutes flat. An adult beaver weighs in at 35 to 65 pounds; much of their weight is pure muscle, which they put to good purpose, hauling timber from woods to water so they can build dams and lodges. Beavers’ feet are webbed, making them superb swimmers and divers.
Beavers are social creatures. The adults mate for life, and the young (called kits) are born overwinter. They’ll stay in the family lodge and help care for the next generation before the adults show them the door at about two years old.
Beaver lodges usually have at least two entrances, both of them underwater to help protect the home from predators. A lodge is often spacious, with several rooms — a feeding den, a sleeping den and sometimes a separate nursery den. They also have air conditioning of sorts, a small tunnel or hole to bring in cool, fresh air from outside.
Lodges come in two flavors: bank lodges, which are built right up against a river or lake bank, and hut or island lodges, which rest on mud in shallow water, away from the bank or on a small island. Hut lodges predominate where beavers have dammed and flooded creeks and relatively small streams; there’s a limit even to beaver ingenuity that keeps them from damming large streams and rivers. Beavers typically build bank lodges in larger bodies of water, like rivers and lakes.
Adult beavers have few enemies in Maryland, now that wolves and mountain lions no longer roam our woods. And while the kits are vulnerable to foxes, bobcats, coyotes, dogs and even snapping turtles, vehicles are the biggest threat to Maryland’s beavers. Vehicles and hunters: Beavers are once again so common here that the state allows trapping during a specified season.
Dusk is the prime time to see beavers. You can easily spot them at Lake Artemesia, paddling at sunset and feeding in the grasses and water plants at the lake edge. Listen for the distinctive percussive slap of their broad tails on the water if they get alarmed, or annoyed by people or dogs that get too close. And look for the wire cages protecting vulnerable lakeside trees, or the gnawed stumps of trees that weren’t protected.
And if you’re eager to hear that percussive tail slap while you’re sitting in your living room, take a listen to one I recorded down at the lake: https://tinyurl.com/2p8s8wz3
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Have questions for Rick about the world of nature in and around the city, or suggestions for future College Park Wild columns? Drop him a note at rborchelt@gmail.com
