How does the color of a bird’s wings help it fly? Many birds that soar and glide have wings that are darker on the top than on the bottom because radiated heat helps them to fly.
Birds usually have wings that are a different color on the top to that on the bottom. The general reason for this is down to camouflage, but recent discoveries have shown a second reason for larger birds. The camouflage idea is easy to understand and can be seen in the sea as well as with birds in the air. A lot of birds have a white, or a whiteish underside and a darker topside. The purpose of this is to hide from predators. When viewed from underneath, they want to blend in with the sky and the clouds, hence the lighter color. When viewed from above, they want to blend I with the land, hence the darker color. This doesn’t apply to all birds, but it is a commonly found adaptation. You can see the same thing in the sea as well. Penguins and sting rays have a lighter underside and a darker topside. When viewed from below, they want to blend in with the sky, and when viewed from above, they want to blend in with the darker sea. This is a good reason for having two shades, but it turns out that there might be another reason.
It turns out that a lot of larger birds may have two colors on their wings because it helps them to fly more easily. I say “may” because this is only conjecture and the scientists who did the study can’t say for definite if there is a strong connection to the color of the wing.
There are three ways that birds can fly. The first way is by flapping their wings. They angle their wings so that the downstroke produces thrust and the air moving over the wings produces lift. Depending on the size of their wings, some birds can get more lift from a single flap and some birds have to flap a lot to get their lift, such as the hummingbird. The second way is to glide. A bird can spread its wings out and glide through the air. The lift comes from the air moving over the wings and the thrust is produced by the force of gravity pulling the bird down. Without flapping, the length of time a bird can glide for is limited because at some point they will have to land. The last method is to soar. When a bird soars, they have their wings in a fixed position, similar to gliding, but they get their thrust from the rising heat, the energy, in the atmosphere.
Whatever method birds use to fly, they have to overcome drag. This is either from the wind they are flying into, or simply drag from the friction with the air itself. The more drag birds have, the more thrust they have to find to get lift. If they are using thermals to soar and glide, then too much drag from the air will cancel out the thrust they get from the thermals and they won’t be able to soar for as long, or they will have to flap and supply the thrust with their own energy. What the experimenters discovered was, birds with darker feathers on the topside of their wings radiated more heat. We all know this from wearing white or black T-shirts outside in the summer. If you wear a white T-shirt, it will reflect the sunlight and stay cool. If you wear a black T-shirt, it will absorb the sunlight and convert the light into heat energy, which it then radiates out. The dark feathers on birds also absorbs the sunlight and radiates it back out as heat. What this does is it heats the air just above the bird. When air is warmed, the molecules have more energy and they move more, making the air less dense. Because the air is less dense, it flows more smoothly over the bird’s wing, reducing the air resistance. It could make enough of a difference to save the birds some energy. It could make it just a little bit easier for large birds to soar. It is still only an observation at the moment, because there are many large birds that don’t have dark top feathers. Or, perhaps, they are just birds that aren’t lucky enough to have evolved this difference. And this is what I learned today.
Sources
https://communities.springernature.com/posts/why-do-gulls-have-grey-wings
https://www.sciencedirect.com/science/article/abs/pii/S0306456517300712?via%3Dihub
https://aviation.stackexchange.com/questions/83556/do-black-wings-have-better-aerodynamics
Image By JJ Harrison (https://tiny.jjharrison.com.au/t/fCEqOJC1cJUcoIOa) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18290910
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