black on white - a bit more

To: "'Geoffrey Dabb'" <>, <>
Subject: black on white - a bit more
From: "Philip Veerman" <>
Date: Sun, 12 Feb 2012 15:02:40 +1100
Good photos and ideas. I can add that it is of course the layering of the feathers that can create the difference of appearance of upper and lower surface. In all flying birds, the upper surface shows more of the outer web of the main wing feathers, whereas the lower surface shows more of the inner web of these feathers. So a bird that has dark outer web of each secondary feather and light inner web may appear to have very dark upper wings and very pale under wings The same principle is obvious in the speculum colour patch on the wings of ducks for example and lots of raptors show that feature.
In the case of the white ibis, the black patch is filamentous against mostly white. That can be seen on individual feathers but varies. Sure the layering is the main part of the story between upper and lower views but there are other reasons. It is much more obvious when the wing is closed, mainly because all those wispy black bits are bunched up together, so look fairly solid black, whereas on the spread wing, these bits are spread out and not so easy to see. Sort of like taking off a fish net stocking........ Also in most poses seen on a flying bird from below, (because the wing is on the upper, not lower, side of a bird's body) the inner edge of the wing is generally hidden behind the curve of the bird's body, with the inner one or two secondary feathers lying over the lower back to eliminate gaps in the airfoil between the wings. Whereas viewed from above, the inner secondary feathers are usually visible, as they are not hidden behind the bird's body. Geoffrey's photos show this.
-----Original Message-----
From: Geoffrey Dabb [
Sent: Sunday, 12 February 2012 10:48 AM
Subject: [canberrabirds] black on white

On the matter of the visibility of those partially black secondaries on white  ibis in flight, I found the below confirming that the black is not visible from below, but is from above, extent varying on individual birds


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