In the past 20 years I have disturbed great horn owls on the ground ripping
into prey 5 times. Twice the prey was mountain beaver, one time the owl flew
off carrying the remains. I have never seen a barred owl carrying anything
bigger than a baby bunny.

Rob Sandelin
Naturalist, Writer and retired teacher
Overrun with bunnies in Snohomish County

-----Original Message-----
From: tweeters-bounces at mailman1.u.washington.edu
[mailto:tweeters-bounces at mailman1.u.washington.edu] On Behalf Of Doug Will
Sent: Tuesday, July 29, 2014 3:49 PM
To: tweeters at u.washington.edu
Subject: [Tweeters] Mountain beavers as prey of large owls

Tweets,

The origin of this string of emails about Mountain Beavers, Aplodontia rufa,
concerned the frequency of of their use as prey species by larger owls.
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
Owls?
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
Hutchinson.

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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