Bird survey location at a post-assisted woody structure (PAWS) site on the Scott River, CA. Beavers have added chewed stems to the structure, visible in the lower part of the photo. (c) Scott River Watershed Council 2015
Beavers, like humans, are engineers of their own habitats, carrying out construction projects that make more food resources and housing available to them. Recently, beavers have been recognized by land managers as playing a vital role in maintaining diverse stream and riparian habitats. The benefits of beaver impoundments in a watershed include slowing and spreading the flow of water, improving water retention and groundwater recharge, increasing base flows, and lengthening the time in summer when above-ground flows are present. Given that climate change is expected to increase drought and reduce snow pack, water storage from beaver dams may be an effective way to help offset decreased water resources. Beaver dams can also expand the size and complexity of wetlands, providing important habitat for birds, fish, aquatic invertebrates, mammals, and amphibians. Ironically, after decades of trapping and removing ‘pest’ beavers, they are now understood to be a keystone species vital to the health of the land. Beavers have been successfully reintroduced to public and private lands in Washington and Utah to control erosion, capture water during droughts, and improve salmon fisheries.
This fall, KBO entered into a new partnership project with the Scott River Watershed Council near Etna, CA, to monitor ecological changes resulting from the creation of PAWS (post-assisted woody structures) — PAWS are built by people to mimic the beneficial effects of beaver dams. KBO is monitoring changes in bird abundance and diversity at PAWS sites to assess the success of these restoration efforts. Past studies of beavers in New York and Arizona show that active beaver sites, and all of their associated habitat complexity, support more species of birds than sites without beavers. Our partners at the Scott River Watershed Council are also monitoring the effects of PAWS on water quality and quantity, and are ensuring that the short, permeable structures are not barriers to fish passage.
So, why not just “leave it to the beavers?” Actually, not all beavers build dams. Some dig bank burrows into the earthen sides of a waterbody or river channel to create their lodges, particularly on deep lakes, larger rivers, and in places where water flows are too fast to build stable dams. Many beavers observed in the Scott River Valley seem to fall into this category of “bankies”. However, permeable wood structures with water flowing through have been known to be too tempting for beavers to resist. The rushing water can actually trigger dam-building behavior, so the area’s resident beavers may soon be helping humans restore streams in the Scott River valley!