[obol] Re: Cattle Egrets

[Phil Pickering]

Their breeding range has expanded to even more northerly latitudes
than Oregon on the east coast, so genetic-based directional migration
being naturally-selected out by climate doesn't seem likely.

Phil


> Theory only:  The species only reached the western USA in numbers in the
> 1970s.  It had progressed across North America from when it had become
> established in Florida.  The pioneering birds for this range expansion 
> were
> the fall dispersants.  Where they were able to survive the winter they
> established new breeding populations, from which dispersants further
> advanced the species' range.  The dispersants to Oregon couldn't survive 
> the
> winters, and eventually the then rather stagnant populations from where 
> they
> came lost the northwest dispersal gene, since it wasn't successful in
> advancing the species.
>
> OK - I admit I know nothing about genetics... so comments?
>
> Jeff Gilligan