[CT Birds] Thoughts on Varied Thursh

Roy Harvey rmharvey at snet.net
Wed Jan 6 08:25:00 EST 2010

Dave missed another key factor on tracking Varied Thrush occurrences in CT.  Varied Thrush invariably is discovered coming to feeders on private property, so they do not become public knowledge unless the home owner is willing to let it be so.  So they are often just word-of-mouth birds at best.  I have archives of the daily rare bird report going back to December 1999.  In all that time there was just one confirmed Varied Thrush that made it to the reports, from Wilton in September 2008.  I know of four others that did not have the owner's permission to be shared that way.  There was one in Hamden (not the one in Andy Brand's back yard, later than that).  Another was in New Hartford in March/April 2006.  The third was in the vicinity of Kent, Dec 2007 through at least February 2008; I don't think the homeowner allowed anyone to come check it out, but the did photograph it.  Finally, there was a report of one in Bristol in early March 2009 that we were
 unable to get permission to visit.

The last three of those four were known to at least one member of the ARCC, and I expect the first was too.  Hopefully their records are more complete.

Roy Harvey
Beacon Falls, CT

--- On Wed, 1/6/10, David F Provencher <david.f.provencher at dom.com> wrote:

> From: David F Provencher <david.f.provencher at dom.com>
> Subject: Re: [CT Birds] Thoughts on Varied Thursh
> To: "CTBirds" <ctbirds at lists.ctbirding.org>
> Date: Wednesday, January 6, 2010, 7:29 AM
> Dennis,
> Population size is only one parameter that affects
> vagrancy. It is true that a population decline will affect
> vagrancy on a purely empirical basis but using a small
> geopolitical area such as CT may not be the best way to
> quantify that affect. Simply stated, not all vagrants end up
> in CT, so if a particular year sees no Varied Thrushes in CT
> there may still be more in New England overall than usual.
> Other factors that affect vagrancy include weather patterns,
> breeding success (different migratory behavior in immature
> birds versus adults), migratory behavior of the species in
> question (long distance migrant vs short distance, etc),
> food source availability where the vagrant ends up, and of
> course the randomness of discovery (many vagrants are never
> detected and this percentage varies from year to year.) I
> know we have beaten this horse before but extracting
> accurate information from vagrants about a particular
> species population is difficult. If you were to factor in
> the other variables with the vagrant discovery patterns you
> might be able to learn more about what are the most
> influential factors at play in vagrancy to CT. Oh and aren't
> we lucky that there is such a thing as vagrancy in bird
> migration. It makes things so much more interesting,
> regardless of why and how it happens.
> Dave
> Dave Provencher

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