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<html> <body> <font size=3>Food for thought, Steve.<br> Angus<br><br> At 03:24 AM 3/17/2012, Stephen Shaw wrote:<br> <blockquote type=cite class=cite cite="">I had a look at this and while it's interesting as Richard says, it <br> seems iffy, perhaps more on account of the treatment by the blogger <br> than of the original authors. The first three 'straw man' ideas <br> offered as to what function the bird's dark eye-stripe fulfills are <br> pretty unconvincing from the start.<br><br> This bird, a masked shrike, must either be somebody's favorite or just <br> one that was readily available for study, because it doesn't have a <br> particularly prominent eye-stripe. You could pick better birds, over <br> here at least, for such a study (swallow family, two shrikes, both <br> waxwings, black-throated gray warblers), that have much more <br> completely dark eye-surrounding feathers. The idea eventually <br> advanced in principle sounds plausible, that the dark feathers in the <br> eye stripe help reduce the sun's reflection into the eye. This would <br> reduce glare and so increase the visual contrast available to the <br> shrike hunting insects, when perched facing into the sun and looking <br> downwards. If that's the case, though, wouldn't you'd expect that the <br> feathers ABOVE the eye would be black to reduce the sun's reflection, <br> as in chickadees, or do the facial bones under the eye jut out a lot <br> so you'd put the black pigmentation there too (as do AFL-ers)? Just <br> having a dark strip running horizontally through the eye would not <br> seem to be particularly useful for all this.<br><br> Their test of painting the black feathers white to see if this worsens <br> hunting skill (apparently so) is in the right direction, but using <br> gouache paint that is known to contain white pigments (making it <br> unusually white-reflective} may not be. This could easily have made <br> the reflections much larger than those that would arise from having <br> normal light-coloured feathers in that location -- not a fair test of <br> the idea, unless they measured local light reflectance and controlled <br> for this (not reported in the blog). Black feather pigments seem to <br> be melanins, and I'm not sure if you could bleach these out locally, <br> to retain the feathers' reflective textures but turn them whiter. <br> Perhaps some of the birders here might know, if local bleaching has <br> ever been used earlier to mark individual dark birds for identification.<br><br> The glaring omission at least in the blog is that many birds have <br> feather patterns that are known or believed to have species- and/or <br> sex-recognition functions. That this has nothing to do with enhancing <br> visual contrast seems obvious where there are pronounced <br> sex-differences, with completely black headed or black-faced males at <br> least in the breeding season, e.g. american redstart, both orioles, <br> bay-breasted warbler. If the major advantage is to possess <br> anti-sun-reflection eye surrounds for insect-hunting, you'd think that <br> both sexes would have developed it and also retained it year round. <br> Not so.<br><br> Browsing through the warbler pictures in Peterson, an even more <br> frequent feather pattern on the head is to have a supercilium/eyebrow <br> that is white or light coloured. What could that do for vision? -- it <br> would seems like a really bad idea, based on this report, but it is <br> very common. A developmental hangover from the ancestral warbler <br> (bottom of the barrel idea)? Has anyone in the bird world asked this <br> question?<br> Steve, Halifax<br> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br><br> Quoting Richard <sternrichard@gmail.com>:<br> <blockquote type=cite class=cite cite="">Interesting bird related article from the New Scientist<br><br> Zoologger: Unmasking the Zorro of the avian world<br> <a href="http://www.newscientist.com/article/dn21591-zoologger-unmasking-the-zorro-of-the-avian-world.html" eudora="autourl"> http://www.newscientist.com/article/dn21591-zoologger-unmasking-the-zorro-of-the-avian-world.html</a> <br><br> (Sent from Flipboard)<br><br> <br> Richard Stern<br> Sent from my iPad</blockquote><br> </font></blockquote></body> </html>
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