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Warning: All rights reserved. This article appeared in the issue of the National Finch and Softbill Society Bulletin.Volume 21. No. 1. Jan/Feb. 2004. (p. 10-11). Anyone wishing to reproduce this article for another bulletin, newsletter, article, journal, CD, or any other public forum needs express written consent of the NFSS and of the author michael@exoticfinches.com
by Michael Marcotrigiano, NFSS Science Editor
Birds can attain attractive plumage color in several ways, depending on the species. Some have feather structure that reflects certain wavelengths of light (commonly blue), some synthesize pigments and they are deposited in defined areas (commonly browns, rust, and black), and some add to their color by eating pigment and storing it in feathers, beaks, and sometimes feet. One class of pigments that assist some birds in becoming colorful is the carotenoids. These fat-soluble pigments are highly prevalent in plants and some seed. They are characteristically yellow to orange. In most birds that have yellow, orange, or red color, it is only by eating the pigment that they attain such beauty. For example, the red siskin's plumage is red because its genetics allow it to accumulate red and orange pigment from food. Through hybridization, these genes have been transferred over to red factor canaries. Another example, is the orange beaks of zebra finches which accumulate these pigments.
Besides making the world more colorful, carotenoids are powerful antioxidants and antioxidants play a key role in the enhancement of the immune response in animals. Over the past decade, one hypothesis for why female birds prefer the most highly ornamental males is that by having intense colors the males are perceived as being healthier, not "just better looking".
Several years ago I was watching the Tonight Show when Billy Crystal came on, impersonating the Latin movie star and heartthrob, Fernando Lamas. Johnny Carson, playing along with the new Crystal character, asked him how his health was and he said in a Fernando voice, "Not great… but Johnny, it is always better to look good than to feel good". Apparently, this is not how it works, at least in the birds studied so far. In fact, there is evidence supporting the prediction that caro-tenoid-based sexual attraction signals are reduced in birds that are infected with parasites, the assumption being that when carotenoids are limited, the bird needs to use its antioxidants for health reasons, rather than for display.
Very recently, in the prestigious journal Science, J.D. Blount and colleagues report on immune function and sexual attractiveness in zebra finches. This is the first report that clearly demonstrates that the manipulation of dietary carotenoid supply causes parallel changes in the immune function and the sexual attractiveness of male zebra finches.
I report on this research to show you that interesting biological work is being done on many aspects in birds. This is not a recommendation to pump up your birds on super doses of carotenoids. Anyone who knows an obsessive color-factor canary breeder is aware that the use of high doses of these pigments can result in liver and kidney failure. What you should gain from this, is an appreciation that a female zebra finch prefers males with more intensely colored beaks and that this is correlated to better health in these studies. So when you wake up tomorrow, comb your hair, brush your teeth, and have a carrot. If you don't attract a mate, eat two.
References
Blount JD, Metcalfe NB, Birkhead TR and Surai PF. 2003. "Carotenoid modulation of immune function and sexual attractiveness in zebra finches". Science 300 (5616): 125-127.
Moller AP, Biard C, Blount JD, Houston DC, Ninni P, Saino N and Surai PF. 2000. "Carotenoid-dependent signals: Indica-tors of foraging efficiency, immunocompetence or detoxification ability?". Avian and Poultry Biology Review 11 (3): 137-159.