Rob & Dennis et al.

I have long suspected that if we had an army of fanatical twitchers
camped out in the Tri-Cities throughout the peak of migration we'd turn
up quite a bit. In fact, there are a rather disproportionate number of
rarities from those locations despite the fact that it's mostly Bob
Woodley who gets out looking.

However, if the Dave DeSante thesis is correct, many vagrant fall
warblers,... predominantly juveniles, are mirror-image reversal
misdirected migrants. He plotted the straight line migratory path for
Blackpoll Warblers from the center of their breeding range to the center
of their staging point on the Atlantic coast, then flipped that line
around the N-S axis, calculated the modal departure date and rate of
movement, and lo & behold he "predicted" the time and place of greatest
concentration of vagrants on the central California coast ca. Sept. 20.
If fall juvenile vagrant warblers of other species follow this pattern it
would go a long way toward accounting for our poor luck with vagrants, as
we are very much further from the modal paths of such vagrants than
Malheur, for example, especially on the coast.

That still leaves the spring to explain.

Gene.

On Mon, 16 May 1994, Rob Thorn wrote:

> 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
>
>