It's always worthwhile consider what Richard Dawkins calls "the
tyranny of the discontinuous mind" when considering topics like this:
the "tyranny" comes from believing that because you have discontinuous
concept names that all things fit one of the concepts discretely.

How do you draw a crisp line between "post-breeding dispersal" and
"migration"? You can't!

Charlie Wright gives a fine example in his Black-headed Grosbeaks
heading to NW Mexico before heading to their wintering sites: so is
that post-breeding dispersal or migration or a bit of both?

http://www.sciencemusings.com/2007/07/tyranny-of-discontinuous-mind.html

http://erweb2.eresources.com/bookshelf/pub/richard-dawkins

I have mentioned this before when talking about Larid complex and ring
species (it's either A or B except when it is some of A and some of B).

I think it applies here too.

On Aug 25, 2009, at 5:41 PM, Charlie Wright wrote:

> Basically, I think the issue is a lot more complex than Wayne
> suggests. I don't think putting all of these birds into the catch-
> all category of "post-breeding dispersers" solves anything. Each
> species deserves to be studied at a finer detail than that.

--
Kevin Purcell
kevinpurcell at pobox.com