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magpie (fwd)



Hi c-birders,

An ornithologist from CCU in Conway, SC (former home of Andreas 
Kristensen, the stringer-slayer) sent me some comments correcting and 
amplifying what I said about melanins in birds, and the appearance of 
aberrant white patches in otherwise black birds. For those who are 
interested, read on...

Joshua S. Rose
Duke University
Department of Biology (Zoology, R.I.P.)

jsr6@acpub.duke.edu
http://www.duke.edu/~jsr6/

---------- Forwarded message ----------
Date: Thu, 18 Jan 2001 15:02:25 -0500 (EST)
From: chris hill <chill@kingfish.coastal.edu>
To: jsr6@duke.edu
Subject: magpie

Hi Josh, 

I'm not on carolina birds right now, but read it on Jack Siler's page.  
I'd add two things to your discussion.

Not only blacks in bird plumage, but also browns, grays, rufous, and buffy
yellows are all due to melanins, which are found in the plumage of almost
all birds (not just black ones). In addition, I don't think melanins are
that expensive to make. They're made from tyrosine (so says Gill's
ornithology text), a common amino acid.  While there's some metabolic
cost, I bet it's fairly trivial compared to cost of making the feather
itself.  Birds that are temporarily starved during feather growth do
develop a weak spot in the growing feather (aka "hunger trace") but I
don't remember ever seeing a change in feather color around the hunger
trace.

I've been seeing the occasional crow with white wing patches since my
teens (twenty years ago).  I was less prudent than Russ Palmieri - I
thought "Jackdaw!" on the first one before I thought magpie.  And Jackdaws
don't even look like that.  Although I haven't persuaded many others, I
think in many cases what appears to be white feathers are often more
transparent than white (I've seen blue sky through one white wing patch).  
I've wondered if crows might be more prone to particularly vigorous
feather parasites.  The effect might be exaggerated if the parasites went
for the more pigmented areas first.

A point in favor of the parasite hypothesis would be if more
"white-winged" crows turned up in summer (i.e., when the flight feathers
are oldest, before the August molt).  Russ's bird doesn't fit that
pattern, most of mine do, but I haven't collected reports systematically.
Of course, capturing a couple would help define the cause, too (good
luck!!).

Chris


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