Hi Peter
If anyone could please try to confirm the id for me, the four blurry
photos are at:
m("N00","//www.flickr.com/photos/29752866");">http:
It's a White-winged Triller as you suspected. The white-edged wing coverts
and secondaries are a good feature of Triller versus Jacky Winter, as is the
contrasting grey rump, clearly visible in the second pic.
Birds without a trace of white at the edge of the tail often appear to have
a contrasting white edge. This is because the outer web of the outermost
tail feather can be exposed without any overlap by more inner feathers. The
edge of each feather, by itself, can be quite translucent, and can let a lot
of light through from behind, making it look pale. The rest of the tail
feathers look a lot darker because they are overlapping each other, greatly
reducing the transparency (and they may be more solidly formed, as well).
Whether it is white or grey means nothing in this context - these are only
relative degrees of darkness which only mean something in comparison to
other nearby objects. Grey can look either white or black depending on what
it is being compared to. The tail is quite dark overall, so if the outer
edge is visible, it is likely to look a lot paler than the rest of the tail,
and could therefore appear as white.
The best way to determine the real colour of the outer tail feathers is to
view them from below when the tail is closed right up. That way you see the
undersurfaces of the outer rectrices against the dark background of the rest
of the tail. It works for the same reason that a bird in general is much
easier to see if it is against a dark background, rather than a pale
background. You can see this easily by looking at a bird against the sky,
when it will often look silhouetted and it can be very difficult to get a
good appreciation of the colour. Often, all you have to do is move a little
so the bird is visible against a dark background, such as the trunk of a
distant tree, and you will see it much better.
Cheers, Chris.
Chris Corben
www.hoarybat.com
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