Q: Which of these two statements is correct?
Yes, there is a bluebird - Or - No, there are no blue birds.
A: (You’re gonna hate this!) Both!
Now, how can that be? Have birds and nature become so politically correct as to please everyone, and no one, at the same time?
Actually, the answer is found somewhere within the space between human language and physics.
There are many blue-looking birds out there. Many even have blue in their names - blue jay, blue-winged teal, black-throated blue warbler (great name for a great little bird). Some birds have “bluish” names like indigo bunting and cerulean warbler. There are even a few that are blue wannabes - great blue heron (they are about as blue as one of those blue tick pointer dogs). Why, there is even one called a bluebird!
Within the ability of our eyes and brains to interpret colors, most of these birds appear plainly blue. And that is okay, and true, inasmuch as our dependable eyes tend to send to our brains only the information that they receive. In the sense of spectral color coming from these bird’s feathers that information is blue color.
But…and as an interpretive naturalist I have become a great ‘but’ fan…is this the true color of these birds’ feathers?
As these feathers export light, the answer is, “Yes!” As these feathers are pigmented, the answer is, “No!” So, here we go again!
But wait, there is a best part…throughout the entire world, and the known galaxy, there isn’t a single blue feather being naturally sported by any bird!
So, where does this blue color come from? Is it some sort of optical illusion? It is! But more than that, it is two optical illusions.
The physics of it is that objects can - in a simplistic fashion - absorb and reflect light. The absorbed color is negated. The reflected light is invisibly sent off into space. If, by chance, however, this reflected light is caught by an eye, and subsequently interpreted by a brain, then it becomes color.
This does sound truly weird, but light is invisible until it meets the eye. Things such as sunbeams, flashlight beams, and even lasers, are invisible unless they are reflected by some medium such as dust, smoke, and water vapor. These tiny objects - particulates to some - become the reflectors that bring the light to your eye for interpretation. Think about things in outer space, where there is mostly a clean vacuum - like some picture of the space shuttle or Hubble telescope. Sunbeams are not visible - just the black void of space. In an opposite sense, think of any movie where a flashlight is used - think of Jurassic Park. Those bright-beamed flashlights would look pretty insignificant if there were no smoke or fog to reflect their beams.
Now, back to those blue feathers.
Like all feathers, blue ones can reflect light in a couple of ways. If the surface is smooth - microscopically smooth - it can allow the pigment inside of the feather to dominate the reflection. This takes place on the molecular level and involves a bit of a prismatic effect.
Prisms are neat. It seems like they can take any light and turn it into a rainbow. But some specifically deformed prisms can retain certain colors and only reflect others. Pretty sneaky, huh? So, even a black-pigmented feather can look blue!
Most blue birds have smooth surfaced feathers, and the absorption and reflection of light takes place inside the feather. The outcome can be quite spectacular. Just picture all the tones of blue on a blue jay. Now, there’s a prismatic work of art - especially given that the bird does not have a single blue feather on its body.
The other optical illusion is called iridescence, and it is quite common in birds. Here, the surface of the feather - again microscopically - has a scratched, or furrowed pattern. This is where the feather does its absorbing and reflecting of light. With a specific pattern of scratches or furrows, the feathers can give off a quite specific prismatic effect. Ducks and hummingbirds have the telltale shininess of iridescence.
I know that a mallard is not blue, but look at its head. Those are black feathers! At most angles the feathers show off as green. But take a look sometime when a mallard swims directly away from you - that’s when its green head will turn purple! This is a common aspect of iridescence.
So, how about that quiz again? There isn’t a single blue feather in the bird world, but thanks to physics, there are plenty of blue-looking birds. And, in at least one little way, it is quite a good reflection upon us.