[Tweeters] Mountain beavers as prey of large owls

Doug Will diwill at uw.edu
Tue Jul 29 15:49:04 PDT 2014


The origin of this string of emails about Mountain Beavers, Aplodontia
rufa, concerned the frequency of of their use as prey species by larger
It seems quite likely that they are taken by Great Horned Owls and quite
possibly by Great Grey Owls. Snowy Owls and Barred Owls could also take
these as prey on occasion.

Barred Owls, by far the smallest of these four owls, seem to prefer mice
over rats (per a private communication from Jamie Acker, one of our
local owl experts, based on his personal experience). Mice run about 100
g whereas rats run 500 g to 1 kg. Aplodontia are typically another
factor of two or so heavier. Over the last couple decades Barred Owls
have also become the most common large owl in our area (western
Washington). So the questions at the heart of this discussion is these:
What portion of a Barred owl's diet by weight is made up of Aplodontia?
And the converse, what fraction of Aplodontia predation is due to Barred
Best data on the first question might come from study of a generous
collection of Barred Owls pellets.
The second question is, I believe, the one that most interested Dave

Perhaps someone associated with the Burke or the Slater knows of such a
study of Barred Owl pellets.
I have been told informally that Barred Owls pellets typically are found
only in disintegrating condition (perhaps because of our moist climate?).

Doug Will
UW and Lake Forest Park
diwill at uw dot edu

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