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