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> Hi Lance and other eye-stripers, Quoting "Laviolette, Lance (EXP)" <lance.laviolette@lmco.com>: > Hi Steve, Richard and others, > > Since athletes have been brought up in the discussion, here is a > summary from the program Mythbusters on the Discovery Channel which > tested whether eye black gave players an advantage or whether it was > simply a myth. > > Explanation: In 1942, Washington Redskins' fullback Andy Farkas hit > the football field with ash from a burnt cork smeared below his > eyes. Today, these iconically sooty swipes have evolved into a > variety of synthetic substances worn by football and baseball > players alike. > > But does eye black really absorb light and prevent glare as some > players suggest? The MythBusters put this smear campaign to the test > to uncover eye black's visual advantage, using a light meter to > measure its effectiveness. Interesting: didn't see this episode -- maybe it's still viewable somewhere? Sounds from your description like they measured the light reflected back from the face with and without the black smears, which if so, isn't really what they should have done. First, things that 'look black' really do reflect less light back than things that look 'light' (amazingly - no need for a light meter!), though even the best blacks like candle soot still do reflect back some light. That's not the real question, which is what's going on inside the eye. How much of the original white reflection from just below the human eye actually enters it, compared to what's entering from the object being viewed? If the former is only 1% of the object's average illumination, cutting this part down to 0.1% with black undereye won't make any noticeable difference to visual contrast discrimination for objects. If instead it's 50% (now a problem), cutting it back to 5% would likely make a big difference. You'd have to test this perceptually by fairly standard methods, by finding what minimum level of contrast individuals can detect with the black undereye smears, and without, to see if there's a significant difference. Maybe they actually did this? > Turns out, indirect light does more than make players blink. It > creates "veiling glare," which reduces their ability to see clearly. > Wearing eye black won't keep this optical phenomenon from happening, > but it can tone it down. The stripes improve the eye's ability to > differentiate between light and dark, and that increased contrast > means you can see in greater detail. The better you can see the > minutia around you, the better you can track an object as its speed > increases - which is obviously important to outfielders following a > pop fly's sunward trajectory. This is dead right, IF the amount reflected into the eye from the face region under the eye is a significant fraction of the whole light caboodle entering -- questioned above. Looking into the sun is a whole new ball game, so to speak, because the sun's disk viewed directly is around 300,000 times brighter than the best blue sky viewed in the same conditions: any reflections from the face pale into insignificance compared to direct 'entoptic scatter' from the sun's illumination of the eye (light scattered inside the eye that's glare, and not part of what you are trying to image). > > Does donning eye black improve athletic performance? While the > MythBusters can't blindly guarantee its effects are a game-winner, > they can see one thing clearly: Eye black can give a baseballer's > eyesight a definite boost. > > Given this finding I'd expect to see most of the raptors and aerial > insectivores with black near the eyes. Many raptors do, particularly > the bird hunters (e.g. the accipiters and falcons). However, > immature accipiters don't have 'black' around the eyes. > > A number of aerial foragers also have 'dark' faces, though again > there is often an age and even a male versus female difference. > Perhaps it is enough to have dark areas under the eye as opposed to > light or perhaps there are differences in the prey they exploit. > However, many of the small flycatchers have white eye-rings which > seems to be counter to what we would expect. That struck me too in Peterson and Sibley, but perhaps the white eye rings are set into the head well below the corneal front surface, so that they reflect light out again from the head (as a species recognition signal), but very little actually enters into the eye of the bird itself. It doesn't look that way with a white supercilium/ eyebrow though. > > The trait is also found in birds that don't specialize in catching > prey on the wing (e.g. Black-and-White Warblers and Red-breasted > Nuthatches who are primarily bark and leaf gleaners), though they do > catch insects in flight from time to time. > > It could be that for many species this is an enhancement to vision, > for others it's a courtship trait, for others it is disruptive > camouflage and for some it may even be primarily to prevent feather > wear (black areas of feathers are tougher than non-black areas). Or, > it may be some combination of these. -- Agreed, probably many functions. I checked a bit more and the black pigment in feathers is indeed recognized as melanin. Melanin can be bleached with a dilute solution of permanganate, so now I just need to find some discarded crow feathers to try this. Surprisingly, one source said that black feathers are more rapidly degraded by bacteria than white ones. Cheers, Steve (at an undisclosable Location, but maybe somewhere in Halifax) > All the best, > > Lance > > Lance Laviolette > Glen Robertson, Ontario > lance.laviolette@lmco.com > > > -----Original Message----- > From: naturens-owner@chebucto.ns.ca > [mailto:naturens-owner@chebucto.ns.ca] On Behalf Of Stephen R. Shaw > Sent: Saturday, March 17, 2012 2:24 AM > To: naturens@chebucto.ns.ca > Subject: EXTERNAL: Re: [NatureNS] Article: Zoologger: Unmasking the > Zorro of the avian world > > 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 complete