Tweeters,

As I was the one who started this thread on Screech-Owl declines (in
response to a question by Jon Anderson about whether Barred Owls ever
preyed on Screech-Owls), I would like to take the opportunity to reply
to Charles Swift's message.

First of all, it should be noted that there are two subspecies of
Western Screech-Owl in Washington: (1) Otus kennicottii kennicottii in
western Washington, which probably shares nearly all of its habitat
with Barred Owls; and (2) Otus kennicottii macfarlanei east of the
Cascade crest, which probably has little interaction with Barred Owls,
because Barred Owls are generally found in a higher elevation range in
eastern Washington. In the southern interior of BC, "macfarlanei" is
found mainly in riparian habitats in the valleys, whereas Barred Owls
are mainly in conifer forest above 3000 feet altitude. The same is
probably true to some degree in eastern Washington.

In BC, "macfarlanei" is appropriately listed by the provincial
Conservation Data Centre as being on the "red list" (equals threatened
or endangered status). The precarious state of macfarlanei populations
is probably mainly because of habitat loss. (More than 90% of riparian
vegetation has been destroyed in some valleys.) However, "macfarlanei"
numbers, though far lower than 50 or 100 years ago, appear to be
stable over the last 10 to 15 years, while those of "kennicottii"
continue to decline.

The subspecies of coastal BC (including Vancouver Island),
"kennicottii", is on the Conservation Data Centre "blue list", which
is equivalent to "special concern" status, or presumably to the
Washington State "watch list". However, in my opinion, this status is
badly in need of review. Based on records from the last 5 years, it
deserves to be on the "red list" now as much as the other subspecies.

>From the comments of various people on TWEETERS, it is obvious that
there have been significant declines of Western Screech-Owls in at
least parts of western Washington, if not so dramatic as the declines
in coastal BC. These declines need to be demonstrated by systematic
surveys (which could also monitor changes in numbers of Barred Owls).

Charles made passing reference to the Nocturnal Owl Survey in BC,
which is providing information on numbers of owls throughout the
province. Unfortunately, it started too recently (5 years ago) to
document declines of Screech-Owls either on the BC coast or in the
interior. Something like this survey is badly needed in Washington and
elsewhere. The Breeding Bird Survey is good for monitoring populations
of many diurnal bird species, but nearly useless for nocturnal ones
(which is why the Nocturnal Owl Survey was started).

I disagree with Charles that "you need more than anecdotal evidence
for a species to be considered for a watchlist". For a start, this
recommendation conflicts with the "precautionary principle", a basic
tenet of wildlife and fisheries management. For Western Screech-Owls
and a number of other bird species, it may be that anecdotal evidence
is the only kind of evidence we have for a decline. Once a species is
placed on a watchlist (or the "Special Concern" list in BC), this is a
signal that more specific and detailed monitoring studies, which will
provide objective information on population changes, need to be
carried out. Hopefully, placement on such a list will attract funding
to carry out needed studies.

I believe Charles may also have misinterpreted the comments about the
effects of Barred Owls on other owl species, because he used the
subject line "owl competition" in his message. I believe that the
effects of Barred Owls on Spotted Owl populations are mainly
competition, but those of Barred Owls on Western Screech-Owls are
mainly predation (although they could be competition as well).

In southwestern BC, I am certain that habitat loss is NOT the main
cause of recent Western Screech-Owl declines, although it is probably
a contributing factor. In many areas around Vancouver, e.g. parks,
the habitat is little changed from 30 years ago, but Western
Screech-Owls have declined from fairly common to non-existent.

I'd like to repeat the final paragraph of the message I sent out on
March 1, with which I hope Charles (and most of the rest of you) would
agree:

"At any rate, the ecology of Barred Owls deserves far more attention
than it has received in BC and WA (and also in OR and NW CA). They
appear to be a major factor in the decline of both Western
Screech-Owls and Spotted Owls, *but this needs to be confirmed by
thorough scientific studies*."

And by the way, I am a wildlife professional with specific training
and expertise in forest bird ecology (B.Sc. and M.Sc. from the
University of BC, and Ph.D. from Mississippi State University).

Wayne C. Weber
Delta, BC
contopus at telus.net



----- Original Message -----
From: Charles Swift <charless at moscow.com>
To: Tweeters <tweeters at u.washington.edu>
Sent: Wednesday, March 09, 2005 9:27 AM
Subject: [Tweeters] owl competition


Hi All -

Anybody who has taken a wildlife population ecology course will tell
you that it is very hard to prove cause and effect relationships when
it comes to interspecific competition. There could be all sorts of
reasons why Western Screech Owls are declining (if they are
declining) that have nothing to do with Barred Owls. You need
more than anecdotal evidence (although it is a good starting
point) and that can be hard to produce. Although not a professional
myself, I have recently taken a pop. ecology course and this was
really
hammered home - I'd be interested to hear from some of the
professional wildlife folks on tweeters on this topic.

Likewise I would imagine you need more than anecdotal evidence for
a species to be considered for a watchlist. So if there is good
documentation of declines for Western Screech Owl (published or
unpublished data) then I'm sure it would be a good candidate. Of
course owls, being fairly cryptic species, are difficult to census.
Some areas (e.g. Canada) have instituted systematic owl
monitoring projects to try to get at this. Birders can certainly
help with these kinds of projects - for example there are many
Breeding Bird Survey (BBS) routes around the country that go
unrun every year.


thanks, Charles.

~~~~~~~~~~~~~~~~
Charles Swift
charless at moscow.com
Moscow, Idaho
~~~~~~~~~~~~~~~~