T his summer the color of Bullfrog Valley is red, for birds anyway. There are the eponymous Cardinals who literally define their color – Cardinal red. They are year round residents and very common visitors at bird feeders. Cardinals are all red, save a black face and are distinguished by a tuffed head.
North America’s only all red bird is the Summer Tanager, and a summer visitor to the area. The male as noted is all red, sort of a strawberry color while the female is an olive yellow color. They aren’t often seen at feeders because they are insectivores grabbing large numbers of bees and wasps from the air. They are common but not often seen. They are best detected nearby from their sound. They have a distinct call note that sounds like a downward pitched “tsk, tsk, tsk, tsk.”” Also denoted as pit-ti-tuck.”
The Scarlet tanager also spends it summers here. The male is red the female yellowish green, is hard to find in the canopy and is insectivorous. The only difference is this red tanager has black wings. The distinct call note for the Scarlet Tanager is “chick-burrr.”
One more somewhat red bird, now a year round resident, is the house finch. They fill the day at my feeders eating lots and lots of sunflower seed. They are a predominately brown/tan finch, but the males have a red head, throat, and rump.
So much for a little natural history of a few local red birds, now the why and how of red birds. The why is clear. The brighter the color the better, due to it’s signaling fitness to a mate. One of the ways a female measures the health of a possible mate may be via the the proxy of bright colors. It’s true of not only red but any other bright color or combination thereof.
There seem to be a whole complement of genes that “travel” together evolutionarily speaking. Genes that lead to bright colors, or striking patterns, or big antlers for that matter seem to be linked with genes the contribute to fitness. These would be genes for physical or ever immunologic strength, genes for adaptability, or even intelligence. This evolutionary cooperativity has been referred to as a society of genes.
So bright redness is indicative of fitness, the fitter birds succeeding in the game of evolution. Now how about the how? How do bird make or get these bright colors? It’s all in the biochemistry. It turns out that birds redness comes from a birds ability to convert dietary components which contain pale yellow pigments. Bright red birds have an excess of a particular enzyme know as cytochrome P450, an enzyme shared with animals and used mainly to detoxify certain toxins. It also converts pale yellow pigments to bright red pigments.
In a study of red vs yellow domestic canaries, the red variety had thousands of times the cytochrome P450 activity as their yellow conspecifics. The pale yellow pigments are converted to bright red pigments, then deposited in feathers and voila, bright red birds.