Red is the color of…

(fill in the blank…)   It’s time for a science nerd post on Backyard Biology, and I can’t resist summarizing an article I read in Forbes magazine (yes, Forbes does publish very well-written scientific articles) about why birds are red.

Red is the color of … many species of birds. In fact there are over 100 species of birds with a little or a lot of red plumage just in North America.

red birds

The first page of a google search for “red birds” shows a lot of images of cardinals, but many other species with red plumage as well, such as scarlet tanagers, painted buntings, red crested cardinals, flamingos, scarlet macaw, house finch, red crossbill, etc.

But there is no inherent red pigment that colors those feathers that rich, ruby hue — so how do birds manage to achieve their rosy glow?


A beautiful scarlet tanager sitting in my buckeye tree


Male House Finches show some red in the winter, but are brilliantly red on head and breast this spring.

As I have discussed in earlier posts, birds require beta-carotene (a yellow pigment) in their diet, in order to synthesize the red “canthaxanthin” pigment that reflects red light. The newly discovered enzyme responsible for the conversion from yellow carotene to red canthaxanthin pigment is one of a group of liver enzymes responsible for detoxification of ingested contaminants.  That’s the first requirement of achieving a red color.

If the enzyme is also produced in the skin while feathers are forming, then they achieve their full red color, and apparently, the more active the enzyme, the more intense or widespread the red. That enzyme activity during differentiation in the skin is the second requirement for achieving a red color.

So…REDness could be an honest signal (or indicator) of the health and vigor of the individual bird, an important cue for females seeking the most fit mate.

Red is the color of the most fit males.

Red is the color of the most fit males.

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