[Tweeters] Mountain Beaver, Part II

David Hutchinson flora.fauna at live.com
Fri Mar 25 10:12:30 PDT 2011

It has been surprising to see how much interest there has been in Mountain Beaver, as a critter, as a prey species and also as a "predator". I just returned from the meeting of the Washington Chapter of the Wildlife Society in Gig Harbor, where several Tweets were in attendance. I was lucky enough to meet "Miss Mountain Beaver" herself, Wendy Arjo, a consulting wildlife biologist from the Olympia area. In conversation with her I was rapidly able to discover that while many of my observations were good, I had made several incorrect assumptions in my interpretations of aplodontia behaviour.

Firstly, they are not a social animal, their individual territories may be one to two acres and any individual animal may have up to 80 or 90 workings in its aggregation. But therefore muy use of the word "warren" is misleading. Secondly Wendy agreed that while their numbers may in general be increasing, finding workings in new places does not necessarily mean that numbers are increasing, rather that the animals are moving from older more shaded and vegetatively mature sites to ones which are more open and with less mature vegetation. This may produce a "checkerboard" or "mosaic" effect to territories, but does not always indicate that their numbers are increasing. Hence Wendy Arjo's interest is from the point of view of tree growing companies, where aplodontia harvest shoots from or kill recently planted saplings. For such a company, what is an acceptable level of depradation before they believe action must be taken? She also points out that aplodontia range extends from southern BC ro central California and has several subspecies.

Wendy cites Red-tailed Hawk as high on the list of their predators, along with mustelids such as weasels and mink. Certainly Barred and Great-horned Owls are predators in our area. She was dubious that Barn Owl could carry an adult Mountain Beaver, but as the appearance of the latter's young above ground (April through June) coincides with Barn Owl feeding young in the nest in Discovery Park, they also are a likely predator. The weight of aplodontia young is a third that of adults. Aplodontia may be an obscure subject, but Wendy Arjo would make a terrific speaker.

David Hutchinson, Owner
Flora & Fauna: Nature Books
Discovery Gardens: Native Plants
3212 W.Government Way

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