Remember that the environment is not static. Northward migration may be a natural means of range expansion. They explore areas that are, now, lethal. But, as climate changes, as development occurs and changes habitats, the area now becomes livable. In WA we have seen Annas Hunnungirds and Scrub Jays invade and expand. No reason that the Kingbirds would not show the same expansions.

A review of the truly old books on birds (1800s, pre 1950) would show some very interesting changes in distribution.


Hal Michael
Science Outreach Director, Sustainable Fisheries Foundation
Olympia WA
369-459-4005
360-791-7702 (C)
ucd880 at comcast.net

----- Original Message -----

One might postulate that, if all northward ranging Tropical Kingbirds
are doomed to death before reproduction, then the behavior would be
non-adaptive and should be either remain rare or eventually extinguish
itself. There is, however, pretty convincing trend data that suggests
Tropical Kingbird occurrences in the fall are increasing and that
individuals are remaining later. This would be the opposite of rare or
eventually extinguished...

I have seen 6 different Tropical Kingbirds this season on the lower
Columbia. Back in the 90's, they were not even annual in this area.

I explored some of the data last season at:
http://www.surfbirds.com/community-blogs/northcoastdiaries/?p=2506

--
Mike Patterson
Astoria, OR
The history of photons
http://www.surfbirds.com/community-blogs/northcoastdiaries/?p=3005
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