Blue jays and bird colors

by Nancy Olmstead

The woman who lives downstairs from me feeds the pigeons almost every morning.  I know she’s out there when I hear a great swooshing of wings: dozens of pigeons flutter down to our driveway to greet her.  She’ll also put out peanuts for the squirrels.  Sometimes a crafty blue jay slips in there and grabs a peanut.

One of those wily blue jays flew up to the fire escape outside my kitchen window, and as it was adjusting its peanut, I got a good look at it.  Blue jays are such a bright blue color; it’s shocking in our Burlington landscape of brown and gray city birds.

Birds come by their colors in different ways.  The blue of a blue jay is not a pigment; it’s created by the physical structure of the feather.  The color is all in the way the molecules are arrayed.  If you ground up a blue feather, thus breaking apart the structure, there wouldn’t be any color anymore.  If you backlight a blue jay feather, you won’t see the blue anymore.  Next time you find one, place it between your eye and a flashlight beam, or hold it up to the strong sun – no blue.

In contrast, northern cardinals borrow their bright red color from plants.  The carotenoid pigments that make a cardinal red can’t be synthesized by animals; they have to be ingested from plants in a bird’s diet.

What are all those feather colors for, anyway?  Scientists know that birds have good color vision.  In species where the male and female are colored differently, color is usually important in mate choice.  A female American goldfinch is picky about which male she partners up with – a male with lovely, bright yellow color is preferred, while a male with drab plumage could find his partner straying.

Colors can also be structurally important.  The most abundant feather pigment is melanin, which gives strength to areas of the feathers that need to be particularly resistant to wear, like wing tips.  Herring gulls are a good example of a bird with these melanin-rich wing tips – they show up as an almost-black color.  Many terns also have this pattern of dense melanin pigmentation at the wing tips.

I’m not sure what role color plays in the life of a blue jay, but I’d like to find out.  Male and female blue jays look pretty similar to me, so perhaps color isn’t a big deal in mate choice.  Or maybe there are small, subtle color variations that I haven’t picked up on yet.

I should team up with the lady downstairs.  I could bring the blue color chart and maybe she could bring the bag of peanuts.

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