Beaver Ecology 101

beaver life history

Beaver are believed to be monogamous and are a family-oriented species, often living in familial colonies of four to six individuals. A beaver pair typically has a litter of two to four kits, each weighing only a pound at birth. As the kits grow they gradually become more involved in foraging and construction, first hitching a ride on their parents' backs to observe, then practicing with little dams of their own. Beaver are strictly vegetarian, with a preference toward tender aspen shoots and willow branches. When a beaver is about two years old it will leave home and venture out in search of a mate, and so the cycle will start again.

beaver dams

The greatest impact beaver have on the landscape is actually not the beaver themselves, but their dams. Once a pair of beaver settle into an area, they build a lodge made of sticks and mud, and construct a dam. Using trees, vegetation, and mud, beavers block stream flow, causing water to slow down and flow out over the surrounding area forming a pond. Dams provide a number of important services to the ecosystem.

As water builds up behind a beaver dam and spreads out, the water is able to soak down into the soil. The ground begins to act like a sponge, filling up with water in all the nooks and crannies between rocks and soil particles. This helps moderate stream flow. When stream flow is high, like in early spring when there is rain and snow melt, dams act like speed bumps and help slow the water down, reducing the damage of flooding. When flow is low, like in late summer when there is no rain, water is gradually released out of the sponge and back into the stream channel.
As the velocity of water is slowed by the dams, sediment falls out of suspension and builds up on the stream bottom, filling the channel back in and repairing damage from erosion, and also raising the water table.
Beaver dams moderate stream temperature and provide a diversity of habitats. The water that collects in the ground sponge is cooled to 50 degrees Fahrenheit, and is released back into the channel further downstream as a cool upwelling. The edges of beaver ponds, where the water is shallow, are warmed by the sun, creating habitat for amphibians and insects. Plunge pools at the downstream edge of dams provide areas of safety for juvenile fish, and the force of the water produces a gradient of gravels ideal for spawning.

where do we want beavers?

When we talk about streams, they can be classified as either upper order or lower order streams. Upper order streams are those high in a watershed. They are the smaller springs or snowmelt-fed tributaries that later join together to form larger rivers. Lower order streams occur lower in a watershed, and are generally larger. When reintroducing or relocating beavers it is ideal to place them in upper order streams first.

The first couple of beaver dams in a system will take the hardest hit from fast-flowing water, so they are more likely to be successful if they are higher up in the system where there is less water and lower flow. One by one, as the force of the flow is regulated and reduced, the dam complex can creep downstream, each buffered by the flow control of those above it, each providing flow control for the subsequent dams below it.

Another factor is that beaver tend to disperse downstream. If a pair of beaver make their home high in the watershed, every two years their offspring will head out to seek their own mates, and are more likely to head downstream than up. In this way a single pair of beaver can ultimately colonize an entire stream system, making a positive restoration impact at the watershed level.

fun beaver facts

beaver were on the first Canadian postage stamps
Oregon is called "the beaver state"
Oregon State University’s mascot is the beaver
beaver are the second best critter on earth at manipulating and changing their environment (can you guess which is first?!)
beaver can live up to 24 years and grow throughout their entire lives
their front teeth never stop growing, so they must chew on wood in order to keep their teeth the appropriate length
they have a set of transparent eye lids that function like swim goggles, and they can stay under water for up to 15 minutes without coming to the surface
oil from beaver castor glands, known as castoreum, was once used as an ingredient in perfumes
castoreum is sometimes an ingredient in “natural flavorings” of vanilla, raspberry, and strawberry
beaver have special flaps in their ears and nose that close off these orifices when under water
a relative of the North American beaver, the Castoroides ohioensis, lived before the most recent ice age and often weighed more than 200 pounds – thank goodness for ancient humans it was vegetarian!