[Birdtalk] Cassin's Vireo "swarm" imagery

[Tim Avery]

Here are 8 different Vireo's I photographed today at Garr Ranch.  Each
individual is different, and some approach Blue-headed, minus a few
distinctions:

1. Bright Adult, possible Hybrid:
http://timaverybirding.com/photos/sept07/cavi_01.jpg

This is a bird that I think many would jump to as a Blue-headed Vireo.  However,
note that the cheek kind of fades out of blue into white, instead of abruptly
stopping and turning white.  The back is far greener than any typical or bright
Cassin's Vireo I have seen, and the head definitely approaches too dark for
Cassin's.  All this said, this is one of the birds I would assume is in the
hybrid "swarm".

2. Bright Adult probably safe Cassin's:
http://timaverybirding.com/photos/sept07/cavi_02.jpg

Although this bird definitely shows a dark head, the fade on the cheek is very
prominent.  The sides are really bright, but he back was much duller.  This
bird more or less fits the bright adult, however the head may be on the dark
side, againleading to possible hybridization.

3. Another Bright Adult, but more typical than the last one:
http://timaverybirding.com/photos/sept07/cavi_03.jpg

I think this would be a safe Cassin's on the bright side. Note the fade in the
cheek and the fade in the back.  The sides aren't all together too bright, and
the back doesn't contrast enough with the head.  I would assume this is the
extreme bright for a Cassin's.

4. Fairly bright Cassin's:
http://timaverybirding.com/photos/sept07/cavi_04.jpg

Although the line on the face is rather abrupt, the light slate colored head is
right.  The back contrasts a bit, because of how light the head is, fitting a
bright adult fairly well.

5.Another bright adult on the edge of possible hyrbid:
http://timaverybirding.com/photos/sept07/cavi_05.jpg

This bird has a dakr head, and very contrasted back in great lighting.  Again
the cheek fades into white, eliminating Blue-headed, but this bird all around
seems out of "typical" or even "bright" range for a Cassin's.

6. Fairly Typcil adult Cassin's:
http://timaverybirding.com/photos/sept07/cavi_06.jpg

This bird is representative of most normal Cassin's Vireo.  Pale head, dingy
green sides, and a nice fade into the cheek.  The back is a little dark but not
out of range.

7. Bright backed adult:
http://timaverybirding.com/photos/sept07/cavi_07.jpg

this bird has a typical head coloration, but the back is on the bright side. 
Fine for  Cassin's on the bright side.

8.  One more typical adult:
http://timaverybirding.com/photos/sept07/cavi_08.jpg

Again, a light head, dingy sides, and non-contrasting back, this is a fairly
typical adult bird.

Cheers

Tim
Salt Lake City, UT
tanager at timaverybirding.com
http://www.timaverybirding.com
http://www.timavery.com