Rob's statements are well-taken, but there seems no or little chance=
of our
putting observers on Tatoosh or Smith islands through a migration=
season to
test his hypothesis. In addition, both Tatoosh and Smith are rather=
close
to mainland forests in terms of a migrating bird's visual ability,=
and
Destruction Island, well off the coast, would really be the place=
to look
(surely those Brown Shrikes and Dusky Warblers found in California=
stopped
at Destruction Island for a day or so). What a shame access is so=
difficult
to all these places. However, in terms of rarities a single Magnolia
Warbler was found on Protection Island by a birder who lived there=
a year
or more and was in the field almost every day, so--like it or not--there's
no way PI could be called a migrant trap. Because its forest could=
be
checked in a matter of hours, it still seems a good place to check,=
but
Smith and Tatoosh, with really limited trees, would be better. Who
volunteers to live on one of them through a migration? (I'd love=
to, but
I'm not footloose and fancy-free.)

I still think latitude plays a part, and I don't think the West and=
East
are exactly comparable. The great mass of migration across much of=
Canada
and even parts of Alaska flows from Northwest to Southeast in fall,=
as most
of the birds breeding all across the boreal forest are of eastern=
origin
and go back to their "eastern" Neotropical wintering grounds. If=
the
"mirror-image orientation" hypothesis--that is, some birds in fall=
migrate
90=B0 away from their normal direction--has any validity to explain=
eastern
vagrants in the west, then a tiny proportion of migrating birds all=
across
Canada will deviate each fall at right angles from the normal NW-SE=
(or
even WNW-ESE) path. It makes sense for many more birds to hit the
California coast than the Washington coast, as when I look at a map=
of
North America and superimpose on it the ranges of all the "eastern"=
species
of birds, it looks to me that a simple explanation could be that=
there
would be many more birds to the NE (or ENE) of California than of
Washington.

Another way of looking at this is that, all other things being equal,=
fall
vagrancy must increase with decreased latitude, as the farther along=
in
migration a bird going the wrong direction would be, the farther=
away it
would be from its "true" destination. This seems incontrovertible.=
Thus why
not fewer fall vagrants in WA than OR? Now spring vagrancy is another
story, because it should increase with *increased* latitude for the=
same
reason, and we know how many spring vagrants Malheur Refuge gets=
compared
with anywhere in WA. There, Rob's explanation of fewer and more isolated
oases does have a ring of truth about it. It would be interesting=
to
compare WA and OR with regard to proportion of vagrants in spring=
vs. fall;
maybe someone out there will do it. Phil Mattocks has a complete=
list of WA
vagrant records, and many of those from Oregon up to a certain date=
are
published in "Rare Birds of Oregon."

Another fruitful comparison that would be testing the mirror-image
orientation hypothesis would be to compare records of eastern birds=
West
and western birds East. In fall, eastern birds tend to migrate toward=
the S
and SE, but western birds, which typically winter in western Mexico,=
also
tend to fly S or slightly SE, with only a small fraction probably=
on a SW
heading. Thus there should be far fewer vagrant Western Tanagers=
in the
East (mirror image of a SW heading) than Scarlet Tanagers in the=
West
(mirror image of a SE heading); however, I don't think that's the=
case.
There are mitigating factors, the biggest of which is presumably=
prevailing
wind directions. There's a lot of food for thought in the analysis=
of
vagrant patterns, and I don't know if anyone has written much on=
this in
recent years. Dave DeSante, who proposed the mirror-image orientation
hypothesis, may have done some of these analyses in his PhD dissertation,
which I haven't seen.

May your vagrant traps be full each time you check them!

Dennis Paulson
dpaulson at ups.edu