Three years ago, a member of the Ecology Center invited me over to her creekside home to look at something. She had spent some time outside on the creek with her husband and they had seen what they thought was a beaver dam. Confident that beavers belong only in more northern and eastern streams, I took some time to verify this with local experts and then went over to see her "beaver dam". What I saw was quite interesting.

Here on our often forgotten creek was a four foot high dam of chewed sticks and rocks that stretched across the creek and collected water in a large pool behind it. Around was more evidence and several large trees chewed in an unmistakable pattern, a chipped, v-shaped wedge that narrowed like an hourglass until the tree had fallen over. Some trees were simply felled and incorporated right into the dam. Some were only partly cut and others were entirely missing. The dam had sticks of all sizes, each with this chewed pattern. I came back later one evening to confirm my new opinion that my friends were right.

In the fading light I waited for what seemed like hours. The pond behind the dam was large. It reflected the dim sunset light and its mirror surface broke with leaping fish, a welcome distraction from the mosquitoes. Eventually, there was a ripple on the water that became larger and larger. Then, around the bend swam a large animal with its head above the water, a mammal certainly. It swam back and forth in the pond until it was joined by two others. Any remaining doubt I had left was shattered by a deafening slap of a beaver tail on the pond as one of them discovered I was there on the side. There were beavers on Sonoma Creek. I had been told that they haven't been in our county for more than a hundred years.

The beaver, Castor canadensis, is the largest member of the rodent family in North America. It is a relative to the sometimes bear-sized giant beavers that disappeared at the end of the last ice age. The only species left here of this genera, they are now about 3 to 4 feet long as adults. Beaver couples mate for life. Their typical litter of 4 or 5 "kits" are born in spring and can swim almost immediately. They swim well within a week. They stay with their parents until they are two years old, when they become reproductively mature.

Beavers are remarkable animals. They are one of the few animals other than humans that can alter a large area of the environment. In many cases, this dam-building behavior improves local habitat for other native animals and plants. In some places, beavers are actually being reintroduced to create beneficial habitat that humans might have to spend thousands of dollars to otherwise build. They can also cause problems if they dig into a levee or fell trees when those trees are desired. They are the only mammal that can digest wood or cellulose. This is due to microbiota, a mix of bacteria and protozoa, that live in their digestive tract. They can literally eat their houses, though they tend to prefer their diet of willow and other native deciduous tree bark either fresh or from stores set aside for winter. They are strong swimmers and builders and can construct canals to haul logs over long distances. An adult beaver can chew through a 5 inch diameter willow tree in 3 minutes, though they prefer smaller logs and branches for food or to construct their dams and lodges. Because our creek is narrow, beavers here tend to make their home in a burrow in the stream bank with an entrance underwater.

I saw as many as five beavers in the pond that year, before the floods came. The next spring, they were at work again until another large storm came. Then they disappeared and were not seen again. I assumed they had been washed downstream and gave up on our creek. Just last month though, I was working on another area of the creek and came through a thicket to find two more dams. Maybe they feel, like many of us, that our creek is special and worth some extra effort to stay with it.