Subject: Re: migrant traps
Date: May 16 11:23:13 1994
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