These Tree Swallows (Tachycineta bicolor)
were photographed by Martin Reid at Benbrook Lake near Fort Worth,
Tarrant County, Texas on September 18, 2002. There were at least
six TRESs in a mixed group feeding very low and flying exceptionally
close to the observer. Most field guides do not show just how
striking are the white tips to the tertials in Fall birds (Sibley
and the Swallows book being exceptions):
In flight these white tips can combine with the fluffed-over white
flank feathering to create a rather obvious partial white patch
on each side of the rump; again, the excellent Sibley guide is
the only one I can find that points to a small white patch in
this area in flight - but even that reference does not show how
on Fall birds, this can be enhanced by the strong white tertial
tips:
At a distance or in difficult light, such a bird might tempt an
observer to think of Violet-green Swallow (esp. if the bird had
little blue color and thus could be an imm. VGSW) - of course
the clean demarcation of the face is a constant difference, but
this may not be noticable at a distance, when the white rump "patches"
are quite visible:
I also got shots showing the molt progression:
