Wednesday, October 22, 2014

Santa Ynez River Beavers Pulling Through in the Drought

It was with some trepidation that I returned to my study site on the Santa Ynez River on Sunday October 12th 2014. The good news is that a water release was ongoing from Cachuma Reservior (senior water rights is a powerful thing even in drought years!), what I was worried about was that the period of no water was potentially devastating to the beaver. After all the last time I went to this area in late July it was bone dry - so dry the willows and cottonwoods were prematurely shedding their leaves and the only water left was a greasy little pool.

Dry Santa Ynez River late July
In areas where I had found abundant and fresh beaver sign - freshly knawed/felled trees, pulled up cattails, bank burrow slide marks - I found no sign of recent beaver activity. Do they move up or down the river to other sources of water? There is always some release from Cachuma to feed a steelhead creek and there is wastewater release year round further downstream. Or do they seek refuge in golf ponds? There are several golf ponds nearby. Both hypotheses are possible and not necessarily mutually exclusive at this point and not outside the adaptive potential of this animal. The golf pond hypothesis seems more tenable given that upstream and downstream movements towards water would entail movements of several kilometers, with kits in tow potentially, and traversing through other beavers territories. But then again although this drought is exceptional there is always some degree of drying of this river annually after the winter/spring rains and before the first release from Cachuma (usually Sep/Oct). Given that this beaver population, descended as it is from a few individuals released by CDFW in the middle of the last century, is more or less kissing cousins - perhaps territorial claims are lessened a bit in drought times? But that this population has adapted to this unusual water regime over several decades, and survived other droughts before, gave me some glimmer of hope that they indeed had found ways to survive the drought conditions and came back.

The beavers did not disappoint.

The first tentative signs of beaver activity were adjacent to a large beaver pond which can actually be seen to the right in the picture above. Beaver have siphoned off a little side channel to the right and created a nice big pool.

As you can see the vegetation/trees are brown - a testament to how dry the river got. As I investigated the pool I found several trail marks and side channels suggestive of beaver movement between this pool and the main river channel.

They might not be too obvious from the pics these were definite trails/paths created by something going from the pool to the river. That they were created by beaver most likely was substantiated by a recently knawed tree:

All together this was some very promising observation of beaver sign and good evidence hat they had came back into this area of the river. But I was very eager to revisit an interesting area upriver where over the last several months I observed some very suspicious rock piles appearing on the river. Yes these rock piles were either the work of beaver, people, or the Blair Witch.

Here are some pics from May when the river was already well underway in drying up:

From May 2014
As you can they are definite piles of rocks and many people who saw the pics felt that humans had constructed them. What argues against these three rock bridges being constructed by humans is; they are not on a path or hiking trail; on the other side is a steep unscalable oak shrouded hill and cattail marsh; and interestingly as seen on the bottom pic there are two adjacent rock piles. Why would people create two adjacent rock walkways so close in an area of the river that is easily traversed anyways?

from July 2014
With the return of substantial flows to the river on this trip I had my answers and I can almost unequivocally say that these rock piles were created by beaver.

The above pic is actually the single rock pile seen in the pic above. Obvious that the rocks placed down were actually the foundation for what is now seen to be an obvious and growing beaver dam. Not only was the rock pile created by beaver but they were making it as the river was drying up and anticipating the return of water flows. Very Cool.

But what about the twim set of rock piles? Just as it is hard to imagine why humans would construct such a weird design, why would beaver make such a funny design - surely in this stretch of the river, moving at high velocity, it was not an ideal spot to place a dam?

Well if you want to know what my working hypothesis is for those strange Blair-Witch beaver rock pile designs you will just have to tune in later as I will explore this facet and other things I saw on the Santa Ynez River in a later post!!!

Support me on Patreon.
Like antediluvian salad on facebook.
Watch me on Deviantart @NashD1.Subscribe to my youtube channel Duane Nash.


  1. Is there any kind of literature of beavers creating rock dams out there ? Thanks

  2. Beavers use what's available. In Martinez we see them use trash and old leftovers floating downstream. Once we saw them use a prosthetic leg and a golf club in the dam! Our beavers don't have access to rocks so they don't use them, but in the rocky streams of sonoma beaver dams ALWAYS have rocks. There is footage on the BBC of beaver using rocks, and I talked who a woman who lived on the creek in sonoma who said she could hear them at night."Plop" "PLop" "Kerplunk!".

  3. Very interesting research and photo-documentation. Go Beavers!

  4. @Kevin Franck, agree with Heidi. On the Santa Ynez river it becomes apparent, especially when looking at the river from google maps/GEOlocate that it is a highly beaver modified river - with old dams that have fallen into disuse and disrepair all over the place. Rocks form the base and foundation since they are heaviest, and then branches and mud to fill in the gap. I often find myself walking on a bank or spit of land on the Santa Ynez, often times with trees growing on it, and look at it carefully and see that is part of an old beaver construction. In addition to classic beaver dams these beavers seem to be adept at constructing side channels/levees that siphon off a part of the river and use this modified section to build dams upon. Instead of trying to corral the whole flow of the river they are in a sense diverting a part of it that is more easily corralled and pooled up.

  5. The beavers in Lake Tahoes western tribs also build dams of bocce-ball or softball sized rocks.