[CT Birds] An interesting study

Dennis Varza dennisvz at optonline.net
Fri Jun 12 12:56:15 EDT 2009

Hi Folks

I ran across this article which I think others may find interesting  
as well.

It is about how visual characteristics of males can provide  
information about the health of the bird to help females choose the  
best birds.

Carotenoids have been identified as the main pigments involved in the  
expression of Yellow to Red Sexual Signals in fish and birds.  
Carotenoids can be displayed in plumage or soft parts, such as bill,  
feet, eyes etc. They can not be synthesized but must be ingested.   
Also, they are used in the immune response. If a bird displays a lot  
of color, it was skilled in acquiring carotenoids and is healthy. If  
a bird displays little color, then it is less skilled in acquiring  
carotenoids and/or is fighting a disease

This study used Zebra Finch Bill color as a measure of attractiveness  
(Orange vs. Red). First they gave two groups of birds carotenoid  
laced water to produce maximum carotenoid concentration in the blood  
and very colorful bills. Then, one group was given an infection of E.  
coli in order to activate the immune system.

Immune activation diverted carotenoids from blood plasma and this in  
turn affect the expression of the bill color making birds less  
attractive.  This study support the idea that carotenoids have  
important physiological properties that ensure the honesty of  
carotenoid-based sexual traits.

What is meant by “ensure the honesty of carotenoid-based sexual  
traits.” is that females can use bill color as a measure of male  
fitness that can not be “faked”.

Witht respect to Connecticut birds , the most obvious birds  where  
this is relevant are Tanagers and Orioles. Also, I would guess Red- 
winged Blackbirds and American Redstarts. With regard to soft parts,  
I would guess American Oystercatchers would be a prime candidate,  
withe their orange bills and legs.

Right now there are plenty of Oystercatchers at Mlford Pt. and Sandy  
Pt. West Haven. chasing each other around. It might be interesting to  
watch them and see if there are differences in color and if the  
dominant birds have brighter bills

Dennis Varza


An Experimental Test of the Dose-Dependent Effect of Carotenoids and  
Immune Activation on Sexual Signals and Antioxidant Activity 		  
American Naturalist 164 (651-659) 2004

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