[EBB Sightings] Steller's Jay Oddity - color blue

	<4A521F10.3030009 at powersedit.com>

As Ralf Stinson has pointed out, blue colors are created by feather
structure rather than pigment.  

However, depending on the subspecies, there is little if any blue on the
head of a Steller's Jay. The adults have heads which are almost black,
sometimes with a dark or cobalt-blue tinge.  Our subspecies also has pale
blue streaks on the forehead.

The tiny microscopic structures which give rise to structural colors are
usually confined to the edges and tips of the feathers.  Over the course of
time, these feather tips wear down and the fine structures can disappear
leaving the feather a different basal color.  Often the tips of feathers
are a different color than the interior and when the tips wear off, the
interior color is seen.

Some birds such as the Starling and House Sparrow can change plumage
radically, simply by feather wear.  There is no molt needed to bring those
species from winter to breeding plumage.

Back to the Steller's Jays.  At this time of year, adult Steller's Jays
often show considerable wear-and-tear on their feathers and the effect on
the head may be pronounced.  I believe that this is at least part of why we
sometimes see Steller's Jays with brown heads at this time of year.  

On Mon, 06 Jul 2009 08:58:08 -0700, Hilary Powers 
wrote:

>That explanation makes perfect sense... but I think something more must 
>be happening with brown-head Steller's Jays. I saw one once too, from 
>the window of a stopped train, and the effect was really spectacular.
>The head of a Steller's Jay is normally more black than blue, and at 
>least on the bird I was looking at (through binocs and for several 
>minutes) the body was the usual intense blue. Meanwhile, instead of 
>being darker than the body, the head and shoulders were about the same 
>color value, or perhaps a bit lighter - a bright clear brown, almost 
>fawn. I find it hard to imagine a lighting effect that would do that....
>Ralf Stinson wrote:
>> With the exception of a few birds in the old world, no birds have blue
>> pigmentation in their feathers.  A pigment is a chemical that absorbs light
>> of colors that it is not (red pigment absorbs green & blue light, so it
>> looks red).  If you put clear oil on water, you see all the colors of the
>> rainbow being reflected.  So the colors you see are not from any pigment,
>> but from light interference pattern on the thin oil film.  There are
>> microscopic structures in the feather that produce the blue reflected light.
>> So for the blue head of the Jay, the microscopic structures were missing, or
>> the angle of the light was such that you did not see the blue.  The dark
>> blue color comes from brown pigment and the blue refecting microscopic
>> structures.  I have seen bluebirds appear brown because of the lighting.
>> After it moved into sunlight, it appeared blue.
>> 
>> Ralf Stinson
>> 
>> -----Original Message-----
>> From: sightings-bounces at diabloaudubon.com
>> [mailto:sightings-bounces at diabloaudubon.com] On Behalf Of Donald Lewis
>> Sent: Sunday, July 05, 2009 22:40
>> To: MDAS Sightings
>> Subject: [EBB Sightings] Steller's Jay Oddity
>> 
>> Sunday morning,  a Steller's Jay with a totally brown head was feeding a
>> fledgling on our deck. I've never seen a Jay like that. I guess a form of
>> less-than-normal pigmentation but I'm curious if others have seen a similar
>> bird.
>> 
>> Don Lewis
>> Lafayette, CA
>> donlewis at comcast.net

-- 
Joseph Morlan, Pacifica, CA        jmorlan (at) ccsf.edu 
SF Birding Classes start Sept. 15  http://fog.ccsf.edu/~jmorlan/
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