From: knapp@spot.Colorado.EDU (David Knapp)
Subject: RFD: Sci.physics.bird.colors  (wasRe: Blue Sky)
Organization: University of Colorado, Boulder
Date: Fri, 24 Jul 1992 14:47:19 GMT

In article <1992Jul23.223910.1774@samba.oit.unc.edu> Dalcio.Dacol@bbs.oit.unc.edu (Dalcio Dacol) writes:
>In article <1992Jul23.171544.6664@trentu.ca> pyacm@trentu.ca (A Colin Morton) writes:
>>In article <1992Jul23.010953.6388@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:
>>>In article <10018@vice.ICO.TEK.COM> hall@vice.ICO.TEK.COM (Hal Lillywhite)  
>>>writes:
>>>> In article <9930@sun13.scri.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:
>>>> 
>>>> ....
>>>> >George did that routine before blue-corn became popular enough to 
>>>> >show up as corn flakes as well as tortillas, or squid-ink pasta made 
>>>> >it into american grocery stores.  Interesting that there are blue birds 
>>>> >and flowers but not blue animals; where is a biologist when we need one! 
>>>> 
>>>> And I find it peculiar that although there are blue birds, there are
>>>> no blue raptors that I know of.  Can you imagine the advantage a sky-
>>>> blue hawk would have?  His prey would have a very difficult time seeing 
>>>> him until it was too late.  I wonder why such an obvious advantage 
>>>> seems not to have developed.
>>>
>>>Actually, he should be blue on the bottom and dark on top,
>>>so that he ends up blending in when viewed from above or below.
>>>Thats "why" fish are silver on the bottom and dark on top, perhaps
>>>
>>Most raptors are, in fact, white or very light gray on their undersides,
>>with mottled brown top coats.  In most parts of the world inhabited by
>>hawks and the like, partly cloudy or hazy days far outnumber the
>>perfectly clear ones, so this actually works better than a blue
>>underside would -- white shows up less distinctly on a blue background
>>than vice versa.
>>
>>Colin.
>
>	The point, it seems to me, is that any bird, no matter what
>color, when seen from below against the day-time sky is going to look
>like a darkish sillouete. since it is mostly backlit. The brownish-gray
>color does offer some camouflage advantage because in the final
>approach, hawks that hunt in open areas come in at very shallow grazing
>angles and so the bcakground, frrom the prey's point of view is either
>a terrestrial landscape (low hills, bushes, etc) or the distant
>horizon, which in general is not blue, but somewhat grayish (sunset and
>down excluded).
>	Incidentally, birds are animals and therefore there are blue
>animals. There are also blue lizzards, but in mammals it is quite rare
>indeed. In mandrils, a large african baboon, there is blue pigmentation
>on the face.  One should also mention that the blue in bird feathers is
>not produced by pigments, its origin is the same as the blue of the
>sky, namely Rayleigh scattering by tiny air bubbles in the feathers.
>--
>   The opinions expressed are not necessarily those of the University of
>     North Carolina at Chapel Hill, the Campus Office for Information
>        Technology, or the Experimental Bulletin Board Service.
>           internet:  bbs.oit.unc.edu or 152.2.22.80


So are we talking about *African* Blue birds?  But an *African* Blue bird
couldn't carry a coconut all the way to England....




-- 
David Knapp                                      University of Colorado, Boulder
Highly Opinionated, Aging  and                      knapp@spot.colorad.edu
Perpetual Student of Chemistry and Physics.
            Write me for an argument on your favorite subject.