Nature: Sonoma County beavers are watershed heroes

In this, the driest part of the year in Sonoma County, you might take a minute to consider creatures that are increasingly appreciated as watershed heroes - the beavers.

Beavers (Castor canadensis) are aquatic mammals that live in streams and lakes and are well known for building dams and lodges, but they have long been misunderstood, ignored or maligned.

Today, however, scientists and land managers recognize them as a “keystone” species, protecting habitat for many other plants and animals, and providing water security for people.

Have you ever seen a beaver? Don’t mistake them for otters. Beavers are actually members of the rodent family.

They don’t eat fish, and they have big, flat tails. They are herbivores and nibble on all sorts of stream-side vegetation, including willows, cottonwoods and grasses. They are usually shy, and because predators like coyotes and mountain lions hunt them, they construct wood and mud lodges or bank burrows that they access through underwater entrances.

Beavers live in family groups or colonies led by the breeding male and female, and are joined by the juveniles from previous litters who help watch over the kits of the year. At 3, juveniles leave home in search of new territory, sometimes as far away as 30 miles.

Beavers once numbered in the millions all across North America. Because they were prized for their fur, they were largely killed off in the 1700s and 1800s. In California, they were exploited first by the maritime Russian-American fur traders who navigated up and down the coast, and later by fur trapping Mountain Men who came overland from the East.

By the early 1900s, only about 1,000 beavers remained in the state

Over the next several decades, conservationists began to recognize the benefits of beavers and began advocating for an end to over-trapping, even supporting efforts to reintroduce beavers to degraded stream channels. The science began trickling in to substantiate the claim that beaver dams conserve water because, as Brock Dolman explains, they “slow it, spread it and sink it.”

“It turns out that as water backs up behind small temporary dams, it flows out across the floodplain of a stream, giving it an opportunity to water riparian forests, trap sediment and slow the water so that it has time to sink into the gravel and replenish the groundwater,” said Dolman, Occidental Arts and Ecology Center WATER Institute director. And this is only the first of many benefits.

While the merits of the beaver were beginning to be known, the hassle of living with them was also real. Landowners have long been frustrated when beavers chew down their favorite trees, block their culverts or burrow through their levees. One person’s ecosystem engineer is another person’s demolition crew.

So California has maintained a depredation permit system that allows private property owners to kill offending beavers. The state also still maintains a recreational trapping season in the majority of counties. At this time, the status of California’s beaver populations is unclear.

In an effort to promote beaver stewardship, Dolman and Kate Lundquist, also of the Occidental Arts and Ecology Center WATER Institute, have been leading a statewide effort to promote beaver stewardship. They work with farmers, vineyard owners, municipalities and resource agencies across the state to share emerging techniques for receiving the watershed benefits that beavers provide while preventing property damage.

One great example of this win-win approach comes from Martinez, a town that learned to embrace the beavers that moved into Alhambra Creek and threatened to flood an area of town and a major transportation hub. Citizens joined forces with the city to install a simple flow-control device that allows the water to be maintained at an acceptable level without destroying the beaver dams or removing the animals.

What might have been a liability has now been turned into an asset. The city now hosts the Martinez Beaver Festival and promotes these creatures as watchable wildlife, bringing thousands of visitors and supporting the local economy.

“Here in Sonoma County, we see Sonoma County Regional Parks as one of the beavers’ best hopes,” says Lundquist. “Most of the recent observations have been in or near county parks, with the most consistent cluster showing up between Maxwell Farms and Sonoma Valley Regional Parks.”

With that in mind, Lundquist is working with Regional Parks and the Sonoma Ecology Center to host a one day “blitz” of the county to look for beaver signs. On Oct. 8, observers will join teams throughout the county in the first ever “Beaver Blitz.” Register at inaturalist.org/projects/sonoma-county-beaver-blitz.

To learn more about beavers, visit oaec.org/publications/beaver-in-california.

Melanie Parker is the natural resource manager for Sonoma County Regional Parks. Contact her at melanie.parker@sonoma-county.org.