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Index of Subjects I had a look at this and while it's interesting as Richard says, it seems iffy, perhaps more on account of the treatment by the blogger than of the original authors. The first three 'straw man' ideas offered as to what function the bird's dark eye-stripe fulfills are pretty unconvincing from the start. This bird, a masked shrike, must either be somebody's favorite or just one that was readily available for study, because it doesn't have a particularly prominent eye-stripe. You could pick better birds, over here at least, for such a study (swallow family, two shrikes, both waxwings, black-throated gray warblers), that have much more completely dark eye-surrounding feathers. The idea eventually advanced in principle sounds plausible, that the dark feathers in the eye stripe help reduce the sun's reflection into the eye. This would reduce glare and so increase the visual contrast available to the shrike hunting insects, when perched facing into the sun and looking downwards. If that's the case, though, wouldn't you'd expect that the feathers ABOVE the eye would be black to reduce the sun's reflection, as in chickadees, or do the facial bones under the eye jut out a lot so you'd put the black pigmentation there too (as do AFL-ers)? Just having a dark strip running horizontally through the eye would not seem to be particularly useful for all this. Their test of painting the black feathers white to see if this worsens hunting skill (apparently so) is in the right direction, but using gouache paint that is known to contain white pigments (making it unusually white-reflective} may not be. This could easily have made the reflections much larger than those that would arise from having normal light-coloured feathers in that location -- not a fair test of the idea, unless they measured local light reflectance and controlled for this (not reported in the blog). Black feather pigments seem to be melanins, and I'm not sure if you could bleach these out locally, to retain the feathers' reflective textures but turn them whiter. Perhaps some of the birders here might know, if local bleaching has ever been used earlier to mark individual dark birds for identification. The glaring omission at least in the blog is that many birds have feather patterns that are known or believed to have species- and/or sex-recognition functions. That this has nothing to do with enhancing visual contrast seems obvious where there are pronounced sex-differences, with completely black headed or black-faced males at least in the breeding season, e.g. american redstart, both orioles, bay-breasted warbler. If the major advantage is to possess anti-sun-reflection eye surrounds for insect-hunting, you'd think that both sexes would have developed it and also retained it year round. Not so. Browsing through the warbler pictures in Peterson, an even more frequent feather pattern on the head is to have a supercilium/eyebrow that is white or light coloured. What could that do for vision? -- it would seems like a really bad idea, based on this report, but it is very common. A developmental hangover from the ancestral warbler (bottom of the barrel idea)? Has anyone in the bird world asked this question? Steve, Halifax ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Quoting Richard <sternrichard@gmail.com>: > Interesting bird related article from the New Scientist > > Zoologger: Unmasking the Zorro of the avian world > http://www.newscientist.com/article/dn21591-zoologger-unmasking-the-zorro-of-the-avian-world.html > > (Sent from Flipboard) > > > Richard Stern > Sent from my iPad
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Index of Subjects