Feather colours

Subject: Feather colours
From: (Shane Raidal)
Date: Wed, 30 Oct 1996 10:49:28 +0800
Llew Rintoul wrote :

>Does anyone know, offhand, what class of chemical is responsible for 
>the colours found in bird plumage?  Beta-carotenes, perhaps.  Or do the 
>colours we see arise from  optical effects such as interference, liquid 
>crystals (as in beetles, I believe).   Alternatively is there a good 
>reference which may be of assistance.


Most brown, black and grey colours are due to melanin granules deposited in 
the feather during feather growth by special cells called melanocytes. 
Melanin also strengthens keratin - this is why many flight feathers have a 
dark tip.

Red, orange and yellow colours mainly due to carotenoid pigments.  There are 
 600 or so plant carotenoids in nature not all cause pigmentation.  The 
carotenoid group includes the carotenes (vitamin A precursors) and 
xanthophylls and both of these groups contain compounds which are pigments.

Green feathers (with the exception of the Turaco) are due to yellow pigment 
AND refraction of blue light (the same reason why the sky appears blue).  
Thus a blue budgerigar would be green if it had the yellow pigment.  
Microscopic air-cells in the barbs of the feather are the site where 
refraction occurs.  Some feather diseases will upset these air-cells and 
disrupt the refractive process (causing green feathers to appear yellow and 
blue feathers to appear white).

Some birds like the Turaco produce genus or species specific pigments.   
Also many parrots have feather pigments which fluoresce under UV light.

The following reference is very useful even though it is focussed on poultry:

Lucas and Stettenheim (1972) Avian Anatomy - Integument, Parts I and II, 
Agricultural Handbook 362, Agricultural Research Service, USDA. 

Dr Shane Raidal BVSc PhD MACVSc (Avian Health)
Lecturer in Veterinary Pathology
School of Veterinary Studies                
Murdoch University                 phone:  +61 9 360 2418
Perth,WA, 6150                            fax:  +61 9 310 4144  

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