Subject: Re: migrant traps (long)
Date: Jan 13 12:19:17 1995
From: Burton Guttman - guttmanb at elwha.evergreen.edu


I just looked back at some files and discovered that I had saved the old
discussion about migrant traps, or at least some part of it. So for what
it's worth, and to save people the trouble of doing other searches, here
it is.

Burt Guttman guttmanb at elwha.evergreen.edu
The Evergreen State College Voice: 206-866-6000, x. 6755
Olympia, WA 98505 FAX: 206-866-6794
==========================

Date: Thu, 12 May 94 16:38:36 -0700
From: Rob Thorn <rthorn at ups.edu>
Subject: migrant traps

I've been periodically checking the outer part of Point Defiance Park in
Tacoma for two Springs now, waiting for a migrant bonanza that has never
fully appeared. This morning, after an overcast, dreary night in mid-May,
should have been perfect for a big fallout. The totals (40 spp. in 2
hours, of which about half were neotropical migrants) were OK but hardly
impressive. It seems clear that Point Defiance, for all its geographical
appropriateness, is not the nirvana of Northwest migrant traps. What is?
I've spent much of the last 8 Springs and Falls looking for an elusive
coastal migrant trap in western Washington. Where other people see
islands and points, I see potential migrant traps. But nothing has proven
reliable. What are other peoples' experiences here: are there good traps
hidden out there (and if so, where are they), or are we wasting our time
looking? Will we never have a Northwest version of Pt. Reyes?

Rob Thorn, Tacoma/Seattle (rthorn at ups.edu)
=================================

Date: Thu, 12 May 94 17:51:48 -0700
From: Mike Patterson <mpatters at ednet1.osl.or.gov>

> What are other peoples' experiences here: are there good traps
hidden out there (and if so, where are they), or are we wasting our time
looking? Will we never have a Northwest version of Pt. Reyes?

> Rob Thorn, Tacoma/Seattle (rthorn at ups.edu)

I think there are migrant traps aplenty, but what you're looking for are
accessible migrant traps.

Here on the north coast of Oregon we have the south jetty of the Columbia.
About half of the coastal vagrants records from Oregon are from here,
mostly because it's accessible to birder's from Portland. Even so, we do
not get the numbers one hears about from Points Reyes, I think in part,
because jillions of birders go there looking. If I were looking for the
perfect Washington vagrant trap, I'd hike out to the end of Leadbetter
Point and sit in the willows. It's not a very convenient trap however.
I've got SJCR which is 20 mins from my house, when I go to Leadbetter it's
for shorebirds, but without really trying I have seen Mockingbird and Sage
Thrasher there.

And then there are all those interesting islands out in the Sound...

Mike Patterson, Astoria, OR
mpatters at ednet1.osl.or.gov

======================================

Date: Fri, 13 May 94 08:44:00 -0700
From: Eugene Hunn <hunn at u.washington.edu>

Rob,

I think it has to do with the biogeographic fact that we are at or near
the northern end of most West coast migratory paths. The breeding ranges
of most species that pass through W. Washington is somewhere in s or c
British Columbia or se or sc Alaska. So I believe it is our fate never to
enjoy a Pt. Reyes, Pt. Pelee, or High Island experience.

Gene Hunn.

======================================

>From rthorn at ups.edu Mon May 16 15:19:21 1994
Date: Mon, 16 May 94 10:42:54 -0700
From: Rob Thorn <rthorn at ups.edu>
Reply to: tweeters at u.washington.edu
To: Multiple recipients of list <tweeters at u.washington.edu>
Subject: Re: migrant traps

>Rob,
>I think it has to do with the biogeographic fact that we are at or
near the northern end of most West coast migratory paths. The breeding
ranges of most species that pass through W. Washington is somewhere in s
or c British Columbia or se or sc Alaska. So I believe it is our fate
never to enjoy a Pt. Reyes, Pt. Pelee, or High Island experience.

>Gene Hunn.

Gene, Most of the migrants in Pt. Pelee (as well as Whitefish Pt. on
Lake Superior) are moving north into Ontario a distance probably less than
ours moving to Alaska/BC. I believe it has less to do with latitude than
a paucity of accessible, isolated coastal groves. All of the spots you
mention have isolated groves adjacent to large water barriers. It's not
unreasonable to think that Tatoosh or Smith Island might have a similar
effect.

Rob

==================================

Date: Mon, 16 May 94 10:46:07 -0700
From: Dennis Paulson <dpaulson at ups.edu>

I agree entirely with Gene Hunn's assessment of the situation. He and
numerous others in the state have spent a lot of mental energy trying to
pinpoint such hot spots for migrants, and physical energy visiting those
suspected of being good candidates. I would say without hesitation that
there are many places in WA that are worthwhile checking for migrants,
both regular and rare. There are willow groves in the Columbia Basin that
I have found teeming with migrants on a few occasions, but, from all our
experiences put together, the probability of finding something rare (the
Peak Experience that birders seek) at any of them on a given visit is
vanishingly low. Rarities have certainly been found at eastern WA oases
and on small islands such as Tatoosh, for example, where I was amazed to
see a Pygmy Nuthatch in June 1970; Bob Paine claimed to have seen an
Eyebrowed Thrush there years ago, but didn't think anyone would believe
him so didn't write it up. And I agree that Leadbetter Point would be a
good place to look for such birds, but Ralph Widrig, who birded there
almost daily for several years, found only a few such rarities.

The point Gene made is that we are sufficiently out of the migratory
pathway of even wandering "eastern" birds that we just can't expect to
find that many, so there is a strong "needle in a haystack" element here.
This is exacerbated in western WA, which is virtually entirely forested,
but it still has patches of woods at tips of peninsulas that "look good."
Many places with great potential--Washtucna, Ocean Shores, Point Roberts,
the Davenport cemetery, etc.--have come up negative again and again when
checked, and only every once in a while has something shocking turned up.
Is this enough reason to call these places "migrant traps"? I don't think
so. We don't seem to have any place in WA as productive of migrants as
the southern OR oases such as Fields and the Malheur NWR headquarters, and
I have long thought this was a product of latitude, not attitude.

Dennis Paulson
dpaulson at ups.edu
==================================

Date: Mon, 16 May 94 11:23:13 -0700
From: Rob Thorn <rthorn at ups.edu>

It's still hard for me to agree that merely latitude is to blame. As far
as distance is concerned, Many eastern species migrate into central
Canada, so latitude seems hardly a problem. It's also difficult to
believe that Malheur could be so good, while the Columbia Basin, just a
few hundred miles further (if that) could be lacking in most vagrants. It
probably is much more a factor of isolation. With the irrigation in the
Columbia Basin, we simply have no truly isolated oases as are found in the
Great Basin. Even at Vantage, there are willow/cottonwood pockets
scattered all along the Columbia River. The increasing numbers of rare
breeders being found in the Okanogan and NE Washing ton implies that
vagrants are reaching the state every Spring, but it is taking singing
birds on territory to locate them. With so much forest, and no apparent
oases, these birds are not being concentrated anywhere...that we know of
yet.

As for isolated coastal spots, I suspect that we again need very isolated
islands. Puget Sound doesn't have traps because you, and any birds flying
over it can see forest on either side if it needs refreshment. This is
not the case at Point Reyes, where the trees are in little dispersed
pockets. Or at the Farallons, where the choice is even starker: rocky
scrubby islands or water. Latitude has little to do with it: Brier and
Sable Islands in Nova Scotia have terrific vagrant records, including many
southern and western species, despite being at a similar latitude as the
Pacific NW.

What we lack is a vision of an oasis. We are not the East or Midwest,
where huge migrant waves can make many places oases. Our oases should
have incredible isolation to concentrate the few vagrants that we have.
Malheur and the Farallons teach us that lesson. We need to readjust our
concept of an oasis, and start looking at the truly isolated locations.
Tatoosh or Smith Island might be a good start.

Rob
=================================

Date: Mon, 16 May 94 14:40:14 -0700
From: Jerry Tangren <GSW$EN at WSUVM1.CSC.WSU.EDU>

Just a few thoughts on the migrant trap issue.

1) It may be more than latitude. The vagrants on the east coast could be
carried by the prevailing winds. The ones on the west coast have to
migrate in the wrong direction, and are probably reverse image migrants.
At our latitude we would not expect to see any reverse migrants, and on
the west coast we wouldn't expect any weather related migrants.

2) Many of our vagrants are not true vagrants but are individuals pushing
the edge of their species limits. They are quite common just to the east
in Montana or to the north in Canada. There are not enough of these to
produce the huge numbers of vagrants that seem to be following reverse
migration routes through southern Oregon and into California to be
discovered on the coast or in the desert.

3) There are just a lot of vagrants moving through California. Too many
to say they just have the right geography.

4) We might expect to pick up more Eurasian vagrants than we actually do.
It may just be the number of birders, but a lot of birds seem to skip
Washington and end up in California. Witness records of Wheatears, Brown
Shrikes, Red-throated Pipits, and Skylark. These must have flown past our
coast. We do alright, or almost alright, on the waterbirds, but where are
the landbirds?

From: Jerry Tangren, Wenatchee WA
<gsw$en at wsuvm1.csc.wsu.edu>
=====================================

Date: Mon, 16 May 94 14:40:56 -0700
From: Dennis Paulson <dpaulson at ups.edu>

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 90o 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!