[EBB Sightings] Varied thrush photo ops?

Why isn't "irruption" appropriate here? The term is commonly used with 
respect to various northerly species when they disperse, en masse, further 
south than usual during the winter.  Debbie writes that the term is 
generally used to  describe "an atypical population of birds driven from 
their normal habitat through some sort of negative environmental influence." 
I don't know of any particular research that has been done here, but it's 
not unreasonable to believe that the Varied thrushes are pushing further 
south than usual this winter because of something that has occurred (or not 
occurred) within their regular winter range.

Here's an interesting discussion of bird irruptions, one that specifically 
mentions Varied thrushes as an example:

http://www.birdsource.org/ibs/irruption.html

--Doug Greenberg

----- Original Message ----- 
From: "debbie viess" 
To: "Doug Greenberg" ; 
Sent: Saturday, January 06, 2007 8:46 AM
Subject: Re: [EBB Sightings] Varied thrush photo ops?


> As Daniel Edelstein kindly pointed out to me, calling
> the appearance of many more than normal varied thrush
> an "irruption" does disservice to the term as commonly
> used in science. Although the dictionary defines
> irruption as "a sudden increase in an animal
> population", in fact the term is more generally used
> to describe an atypical population of birds driven
> from their normal habitat through some sort of
> negative environmental influence, like when the local
> woods are filled with crossbills (like a magical
> encounter I had with dozens and dozens fluttering into
> a creekbed on Mt. Tam, 20 some years ago), or
> Minnesota seeing an invasion of multiple Snowy Owls
> (like happened recently in the Midwest).
> This is not to say that the large numbers of Varied
> Thrush we are seeing have not been driven here by
> environmental influences. Perhaps we need a new term,
> like migruption?
> Debbie Viess
> --- Doug Greenberg  wrote:
>> Hello all,
>> We all know now that we are seeing the biggest
>> Varied thrush irruption in
>> many years...