[Tweeters] Re: Spotted Owls ( and Barred Owls)

Matt Dufort zeledonia at yahoo.com
Mon Dec 13 19:51:04 PST 2004


I spent this summer surveying forests in southwest Washington for Spotted
Owls, and I can add a few things to this discussion.  Most are somewhat
anecdotal due to the small number of territories I surveyed (perhaps 15),
but are still pretty interesting.

Many of the sites I went to were locations where Spotted Owls were found
historically - within at least the last ten years.  MANY of these sites now
host Barred Owl pairs.  Most of the habitat I was in was fragmented enough
that there were limited patches of forest big enough for either species to
establish a territory.  Most (all?) of the sites in secondary forest, or in
small patches of old-growth (wish I could say exactly how big, but I can't
recall clearly) were either unoccupied by Strix owls or had a pair of Barred
Owls.  In many of them, the Barred Owl pair was in pretty much exactly the
same spot the Spotteds were formerly found (perhaps they're both somewhat
limited by good nest sites?).  Most of the bigger old growth patches had
Spotted Owls.  But there weren't very many patches that size.

One interesting theory on the decline of Spotted Owls in the Pac NW, that I
haven't really seen advanced here, is that the decline we're seeing right
now is due partly to die-off of adults that haven't been reproducing for a
while.  Spotted Owls are pretty marginal in their ability to breed; at best,
Spotted Owls in Washington breed about every other year.  Dealing with
smaller areas of good habitat (or competing with Barred Owls) may make it
impossible for them to build up the resources they need for reproduction
(good physical condition, nutrients required to produce eggs, enough food to
feed young).  They're also relatively long-lived, so maybe those aged birds
are gradually dying off.  This is purely speculation, but it seems like a
possibility.  I'm sure someone has the data to address this question.

On the topic of Spotted vs. Barred Owl diets - my supervisor, who's been
working with Spotted Owls for 10+ years, told me that in Washington, Spotted
Owls feed mostly on two species: Bushy-tailed Woodrat and Northern Flying
Squirrel.  Barred Owls are much more generalist in their diets.  So there is
definitely some ecological difference.  I find it pretty surprising that a
species could get by eating just those two rodents, but that's what he said.
Anyone have info from the Birds of North America account?  One of my
co-workers was lucky enough to see a Spotted Owl catch and eat a flying
squirrel.  Must have been pretty awesome.

Spotted Owl x Barred Owl hybrids are definitely rare.  The same supervisor I
mentioned above said he'd never knowingly encountered one.  I sure didn't
find one this summer.  From recordings that I've heard, they're fairly easy
to differentiate by call from both Spotted and Barred Owls (at least
first-generation hybrids are).  The hybrids' call is usually 5-7 notes, with
a pattern similar to a normal 4-note Spotted call, but each note has a
slurred, descending quality to it.

Regardless, I think the problems of habitat loss and resultant competition
with Barred Owls are much more of a problem than hybridization.

Matt Dufort
Seattle, WA

----- Original Message -----
From: "Wayne C. Weber" <contopus at telus.net>
To: "Stewart Wechsler" <ecostewart at quidnunc.net>
Cc: "TWEETERS" <tweeters at u.washington.edu>
Sent: Sunday, December 12, 2004 9:49 PM
Subject: Re: [Tweeters] ... Spotted Owls ( and Barred Owls)

> Stewart and Tweeters,
> Spotted Owls have indeed hybridized with Barred Owls, producing the
> so-called "Sparred Owl". However, such hybrids are quite rare. I
> believe that fewer than a dozen have been recorded, despite the
> intensive and widespread research on Spotted Owls that has taken place
> over the last 30 years or so.
> However, at a symposium on Spotted Owls (sponsored by the Washington
> chapter of The Wildlife Society) that I attended last year at Port
> Townsend, it became obvious from several presentations that
> competition and displacement by the invading Barred Owl is now a major
> cause of Spotted Owl decline.
> The loss of Spotted Owl habitat has declined because of the Northwest
> Forest Plan, but Spotted Owls continue to decrease at an alarming rate
> in many areas.
> Although Barred Owls tend to prefer second-growth broadleaf, mixed,
> and conifer forests, they are displacing Spotted Owls even from
> old-growth conifer forest in some areas. For example, if I recall
> correctly, there are now few Spotted Owls left below about 2000 feet
> altitude on the Olympic Peninsula, where Barred Owls have displaced
> them even from old-growth.
> The problem is so serious that there was some discussion of whether or
> not it might be necessary to control Barred Owls so that Spotted Owls
> could survive in some areas. However, there is a serious question as
> to whether a Barred Owl control program would be feasible at a
> reasonable cost, or whether it would ever be politically acceptable.
> It would certainly be highly controversial.
> Wayne C. Weber
> Delta, BC
> contopus at telus.net

More information about the Tweeters mailing list