A few days ago I took my daughter for a walk in the canyon, and I took a few photos of recent animal activity along the shoreline.
By Patrick Norton, CSCC volunteer
LEFT: As we were passing over the Cross Canyon bridge (the one with the blue lights) I noticed a collection of shells in the cavity of a rotting log down along the shore.
RIGHT: These shells are the remains of freshwater mussels- probably either the western pearlshell (Margaritifera falcata) or the Oregon floater (Anodontia oregonensis), both of which occur in the watershed. The log was apparently used recently as a feeding platform by a predator which had collected the mussels from the lake bottom. There are three predators in present in the watershed which take mussels: North American river otters (Lutra canadensis), muskrat (Ondatra zibethicus), and mink (Mustela vison). I have not heard of otters being present in the canyon recently, though they are certainly spotted lower down the watershed, and I have not seen muskrat in the canyon for over a year, so it was probably a mink, which have been spotted recently a few yards west (see Zach Perry's post of 11/ 18/2011). Too bad the shore next to the log didn't have a mud or sand substrate to show tracks.
The other thing we saw was evidence of some recent beaver activity along the south shore. Usually beavers select small-diameter trees to cut for food, eating the inner bark (cambium) and the leaves, as well as herbaceous plants. I'm told that when beaver go after mature trees it may be due to insufficient access to normal food sources, since the amount of work required to sever a large tree trunk is very great compared to the amount of food derived. Some of these trees have been girdled (which is fatal to them) and others have been injured only on one side.
RIGHT: This bigleaf maple was cut so deep that the weight of the already leaning tree caused it to split up the trunk about ten feet.
Since none of them have been actually felled it is a mystery to me what the beaver were after, as they must have expended a great deal of energy while not succeeding in gaining access to the small branches which would have given much more food than the small amount of cambium removed in the process. Cutting so deeply into the wood was certainly not required in order to get at the cambium.
: Even the trees protected by wire are fair game for the hungry beaver. I wonder what the cause is. I find it hard to believe that there is not more suitable food to be found nearby, but I suppose that is a question for a wildlife biologist (or Zach Perry- see his blog entry I just found here: http://blogs.reed.edu/reed_canyon/2011/12/welcome-to-beaver-country.html
Time to go home!