[obol] Subject: Black-headed Grosbeaks

[Daniel Farrar]

Obol,
   I think what we are seeing this time of year in songbirds is the
formation of large mixed-species roaming flocks, not necessarily south bound
migration.  Family groups seem to join up with each other and form these
flocks.  At my banding station I see this annually.  It usually starts in
late July.  All of the sudden I start capturing hatch year birds of species
which do not breed within my station boundary.  These birds generally have
very little fat.  Most song birds need to nearly double their body weight in
fat before migrating and it is clearly visible  under the skin when the
specimen is in the hand.  This fat is essentially all burnt off during long
(hundreds or sometimes thousands of miles) night flights.
   I suspect the Grosbeaks you are seeing are in the process of "fattening
up" before heading south.  They are wandering, searching for easy to get
high energy food.  Most simply have not had ample time to fatten fully since
fledging young or since being fledged themselves.  On Tuesday we caught 2 BH
Grosbeaks, both of which had barely any fat and were in no shape to
migrate.  We also happened to catch 2 Bullock's Orioles in the same net
which were almost half way to being fully fattened.  A Western Tanager was
also in the group.  It lacked any fat.
  Just some thoughts.  Happy migration!

Daniel Farrar
Eugene OR
jdanielfarrar at gmail.com

On 8/10/07, Brandon Green <bjgreen34 at yahoo.com> wrote:
>
> And speaking of movement, I've seen an unusually-high number (for me) of
> RUFOUS HUMMERS in my yard over the past week and a half or so.  Looks like
> they're beginning to move south.
>
> Brandon
> Eugene
>
> -----
> *Subject: Black-headed Grosbeaks*
> From: Ray Korpi <rkorpi AT hotmail.com>
> Date: Thu, 9 Aug 2007 21:19:06 -0700
>
> All,
> I have had some calling Black-headed Grosbeaks each of the last four mornings
> in Vancouver, WA. There does seem to be some movement right now,
>
> Ray Korpi
> rkorpi AT hotmail.com
> Vancouver WA
>
>
>
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-- 
Daniel Farrar
Eugene, Oregon
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