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Basic Beaver Biology

By Betsy Washington and Kevin Howe

Indians believed that beavers were the “sacred center” of the land because of their central role in creating rich wetlands that create habitat for many species of mammals, birds, fish, turtles, and frogs. In fact, beaver wetlands are often considered the most biologically diverse community in the temperate climate zone! Most beavers inhabit streams and are famous for their incredible engineering skills used in building elaborate dams and canal systems and shallow ponds. This of course, has created conflicts with humans by cutting trees and flooding forests, agricultural lands, or occasionally roads. Beavers are extremely gentle, playful, and highly intelligent animals. A famous animal behaviorist said, “When we think of the kinds of animal behavior that suggest conscious thinking, the beaver comes naturally to mind”. 

The American beaver is a rodent – the largest in the N. hemisphere. They average about 3 to nearly 4 feet in total length and about 40 pounds. Beavers are readily recognizable by their horizontally flattened, scaly tails.  Beavers use their tail both as a rudder for swimming and navigating while carrying large logs, and also to warn other beavers of danger by slapping their tail against the water with a loud smack and splash. Their back feet are webbed and used to propel themselves through the water at up to 2 mph. Their front feet have specialized digging claws for creating bank burrows and canals.  They have a range of special adaptations that allow them to remain underwater for up to 15 minutes!  

In Lake Barcroft, beavers do not build dams, but instead construct lodges of stripped branches and sticks in the lake bank.  Burrows are typically built under tree roots or shallow docks where beavers interweave thick sticks and logs and plaster these in place with mud. A single lodge may have several entrances all located under water while the living quarter inside the lodge is above water. Beavers are chiefly nocturnal, and spend their daylight hours in their lodges. They can often be seen swimming along the lakeshore in the early morning and at dusk.

Beavers are highly territorial animals and produce a pungent “castor” oil that they deposit on “scent mounds” or small piles of sticks and mud, that mark the boundaries of their territory and serve to keep other beavers away.   

While most everyone knows beavers feed on the inner bark of deciduous trees, what they don’t know is that the spring-summer diet of beavers is about 95% herbaceous plants and roots – especially emergent aquatic vegetation like spadderdock, a waterlily relative. Quite possibly the lack of emergent vegetation in Barcroft is the direct result of the beavers keeping it mowed down.

With the onset of fall, they are especially busy cutting trees and branches. These are used to build up the lodge to protect the home over winter and to provide a cache of food for their larder over the winter. Many tree branches are stuck in the mud at the bottom of the lake near their lodge for food when the lake is frozen.

Beavers have 2 chisel-like, orange lower incisor teeth, which are used for cutting the trees. Beavers can easily fell a 4” diameter tree in about 15 minutes!   Generally they prefer trees less than 6” in diameter, but they have been know to fell a trees over 5’ in diameter. Favorites include fast growing trees with soft wood such as birches, willows, alders, maples, tulip poplars, and dogwoods.  However, beavers are opportunistic and will also take trees with harder wood such as oaks, beeches and even conifers.  

Beavers mate for life and may live for 12 years or more. Young are born in May and June with an average litter size of between 3 and 4 young.  Beavers tend to regulate their own populations levels, so when population levels are high and food is scarce, beavers have fewer young. Beavers are devoted parents and spend much of their time training and instructing their young. A typical beaver colony consists of the parents, young kits and yearlings or “teenagers”.  Parents drive the yearlings out of their territory in their second year, after the new litter of kits is born. 

The Lake Barcroft Beaver Management Policy takes advantage of the natural territorial behavior of our resident beavers in order to effectively and humanely limit beaver populations in the lake and to discourage beaver damage to personal property. This Policy along with tips on protecting your property can be found on the Lake Barcroft website under Environmental Quality.