Wild Creatures among us: Beavers and Mountain Beavers in Shoreline and Lake Forest Park

This female was trapped in Lake Forest Park's Hillside Creek
and relocated by Beavers Northwest
Photo by Kim Josund

By Christine Southwick

The beaver is North America's largest rodent and is built for life in the water. Adults can be up to four feet long and weigh over 60 pounds. The beaver has webbed hind feet and a large, flat, nearly hairless tail.

Photo by Jerry Cahill

It uses its tail to help maintain its balance when it is gnawing on trees. It will also slap its tail against the water to signal danger or to warn away predators.

The beaver has short front legs with heavy claws. Their rear legs are longer, and they use their rear webbed feet help propel themselves through the water. When the beaver is under water, its nose and ears close up and a special membrane covers its eyes.

Beaver at Magnuson Park
Photo by Scott Ramos

Beavers mainly eat tree barks. Beavers also eat other vegetation like roots and buds and other water plants. The beaver has a specialized digestive system that helps it digest tree bark.

Beavers mate for life, but if one mate dies, the other one finds another mate. Beavers mate when they are about three years old. Mating season runs from January and March in cold regions and in late November or December in the south.

Beaver lodge at Magnuson Park
Photo by Scott Ramos

Gestation lasts about three months, and females have one litter of kits a year between April and June. Before birth, the female makes a soft bed in the lodge. The babies' eyes are open when they are born, and they can swim within 24 hours of birth, and they will be exploring outside the lodge with their parents within a few days.

Young beavers are weaned in about two weeks. Both the male and the female take care of the young beavers. They stay with their parents for two years. Beavers can live to be 20 years old.

Locally, beavers are reported at Ronald Bog and Twin Ponds. The one who set up shop in Lake Forest Park was flooding school grounds with her dams and had to be relocated.

Mountain Beaver in Lake Forest Park
Photo by Craig Kerns

Mountain beavers live in moist forests, on ferny slopes, and are occasionally found in damp ravines in urban areas. Their worldwide range is the coastal lowlands and coastal mountains of southern British Columbia (from the Fraser Valley to the Cascade mountains), western Washington, western Oregon, and south into California.

• Mountain beavers are herbivores and eat a wide variety of plants.
• Food items include all above and below-ground parts of ferns, salal, nettles, fireweed, bleeding heart, salmonberry, brambles, dogwoods, vine maples, willows, alders, and conifers. Mountain beavers also eat rhododendrons and other ornamental perennials, shrubs, and trees.
• Food items are eaten on site, temporarily stored outside burrow entrances, or placed in caches inside burrow systems (Fig. 4).
• Mountain beavers will climb into trees to lop off living branches that are up to 1 inch in diameter.
• Mountain beavers have primitive, inefficient kidneys and must drink 1/3 of their body weight in water every day.
• Mountain beavers dig tunnels 6 to 8 inches in diameter throughout their territories, which may be 2 acres or more, depending on food and cover availability, and population density.
• Tunnel systems, or burrow systems, are located in or near thick vegetation, and tend to radiate out from a nest site. Mountain beavers have been found using tunnels that are 10 feet underground.

Mountain Beaver in Lake Forest Park
Photo by Craig Kerns

Mountain beavers are abundant and active year-round, yet they are seldom observed due to their subterranean existence. Although active on and off throughout a 24 hour period, they are only occasionally seen wandering around on the ground or climbing in trees during daylight hours. They find the majority of their food and water within 150 feet of their burrows.

Besides Lake Forest Park, there are mountain beavers on the grounds of Shoreline Community College - and probably in The Highlands as well.