The hard work of beavers can be seen all along the Napa River and its tributaries. Scientists and biologists working in our local waterways estimate there to be at least 20 different colonies (families of beavers) spotted as far up the valley as St. Helena. In Napa, the Tulocay Creek colony has grown popular among locals; mama beaver and her kits (babies) are regularly featured in the Napa Valley Register.
It might seem novel to find these industrious builders in our downtown and neighborhood waterways, but beavers can be traced back to the Napa River for centuries. For many years, scientists were misinformed about the habitats and behaviors of beavers in Northern California and did not consider beavers native to the waterways that feed into the San Francisco Bay. Recently, historians and scientists with the California Department of Fish and Game presented evidence that challenged long held beliefs about where beavers belong, and ecologists are establishing important links between the presence of beavers and the health of our watersheds.
Evidence of beavers has been documented by white trappers and settlers in the Napa River as early as 1832. Many indigenous peoples in our area have a word for beaver in their native language, suggesting that the presence of beavers extends far beyond written records. White settlers widely considered beavers a nuisance; beavers that weren’t killed by trappers were later killed by landowners. Now that scientists are beginning to gain a better understanding of the critical role beavers play in maintaining healthy watersheds, they are looking to change the way people view beavers from pests to protectors of our waterways.
Beavers are best known for the impressive dams they can build across a waterway. Using their powerful teeth to chew down trees and branches, they skillfully intertwine these materials to build their dams. Next they scour the river bottom and shores to gather mud, rocks, leaves, and grasses to seal the barrier walls and slow down the water flow. As the water level rises, it covers the entrance to their home on the nearby riverbank, known as a lodge, to protect the beavers from predators. A colony of beavers may build several dams on a single stretch of waterway to create the ideal conditions for their home. Holding the water back, the dams form deep pools where fish, amphibians, birds, and other mammals come to live.
Beavers are a keystone species in the wetland ecosystem. They play a critical role in providing beneficial habitat and food for a wide range of species, who otherwise wouldn’t be able to thrive in the Napa River. Dams form reservoirs that provide food and shelter for creatures of all sizes, keep water temperatures cooler throughout the warm summer months, and filter fine sediment in water to improve water quality. This provides ideal conditions for the young of threatened species such as chinook salmon and steelhead trout to thrive. Visit a local beaver dam downtown or on Tulocay creek, and you can see a wide range of animals, including turtles, otters, mink, and birds. Beavers transform our waterways from channels prone to erosion to oases of ecological diversity.
Aside from helping other animals, reservoirs created by beaver dams help the land by slowing the flow of water in the river. Rainfall has more time to be absorbed back into the watershed instead of rushing out to the sea, hydrating surrounding soils for longer and keeping tributaries flowing longer into the dry season. Because of this, dams built by beavers make it more likely rivers and streams are able to rebound after a drought season. In addition to slowing down the water to recharge our water supplies, slower flow also helps prevent erosion. Ponds created by dams help support the growth of plants that stabilize riverbanks during high flows and reduce the amount of land lost. The debris also helps absorb the force of the water that would otherwise flow too fast and wash the land on the banks away.
In Napa County, we recognize the valuable contribution of the beavers to our watershed; government organizations including the Flood Control and Water Conservation District as well as the Resource Conservation District work to help beavers and people coexist. Engineers, scientists, and biologists work to make sure development in the valley doesn’t drive the beavers away from their homes, and work with local residents and businesses to prevent and mitigate damages done by beavers as they chew down trees and raise water levels in creeks.
Next time you are near a waterway, keep your eyes open for blocked up streams and large ponds. You might just stumble upon a beaver dam, and all the wonderful animals that come with it!
Check us out! Books and resources available from the Napa County Library:
1). Beavers: Wetland Architects by Megan Borgert-Spaniol
2). Beavers: Construction Experts by Katie Lajiness
3). Beavers Build Lodges by Elizabeth Raum
4). Beavers Audiobook by Rachel A. Koestler-Grack
5). Wildlife LOL: Beavers! by Hilary Auss
6). Superpower Field Guide: Beavers by Rachel Poliquin
6). Five Busy Beavers by Stella Partheniou Grasso
7). La Patita Dorada y los tres castores by Robin Koontz