>You don't count range extensions with leapfrogging such as our
>Black-throated Sparrows and Arctic Terns?
>
>Gene

I didn't, probably because I think of them as peripheral colonists
extending the range outward a bit more than is typical. In these two
cases, (1) the sparrows may well be breeding in the next available habitat
north of their Harney County, OR, breeding grounds, which causes the
disjunctness; and (2) I wouldn't be surprised if there were a few other
tiny Arctic Tern colonies between here and the next-southernmost colony at
Stewart (which may be defunct now), BC. There are very few birders spread
along the vast and tortuous coastline between Vancouver Island and the
more-or-less continuous Arctic Tern populations from the Juneau area, AK,
north. It's certain that there couldn't be a lot of terns in that area, as
someone would have seen them, but maybe a few.

Nevertheless, these *are* good examples of populations dispersing well
beyond the normal range, rather than just a bit beyond it. I've been
continually amazed at the persistence of the Everett Arctic Tern colony,
which seems to me too tiny to persist; but there it is! Arctic Terns
probably live 20+ years, so I guess they have a chance to persist even with
a very low reproductive rate.

In my previous posts I was thinking of colonization by vagrants, i.e.,
something turning up in a very out-of-range location and then remaining
there to breed or starting a wintering or staging population in subsequent
years. If Chestnut-collared Longspurs all of a sudden began to winter in
w. WA, this would represent an example. Perhaps the breeding Little and
Common Black-headed (and, I'll bet eventually Lesser Black-backed) gulls in
North America represent examples. Maybe the Churchill Ross' Gulls are
another. Those gulls!

The population of White-winged Crossbills that colonized the Dominican
Republic is a good example. But this happened sufficiently long ago so
that the population has differentiated considerably, and if colonization
occurred during a glacial period, White-winged Crossbill populations would
have been much closer to the West Indies.

Food for thought, if not quite as sustaining as pumpkin pie (sorry, my mind
drifted to a recent Christmas party).

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416