If you're a city dweller, you see these dirty little birds hopping around every day — might as well know why they look the way they do! Find out what makes pigeon throats shine, and how pigeons compare to other iridescent birds.
Pigeons — more poetically known as rock doves — are a fixture of pretty much every metropolis on the planet. Urban denizens must contend with pigeons cluttering up public plazas, picking through their garbage, and pooping on their cars.
But hey, can we fault them for not dying as obligingly as the rest of nature when exposed to the rigors of urbanization? And they bring a little sparkle to city living — even dull gray pigeons have shimmering pink and green iridescent throats. But how exactly do they maintain this color?
You may guess that the oils on the pigeons' feathers make the birds shimmer, but the iridescence is actually another example of structural color. It's built into the features themselves. The feathers are a tilted latticework of tiny threads of pigmented material.
Light waves hit and bounce off of each of those threads. The light waves then interfere with each other as they head out into the world. Where peaks hit troughs, they cancel each other out and there is no color. Where peaks merge, there is an intense blast of color. Your eyes will be in the path of cancellations and peaks depending on where your head is at any one time. Moving your head (or watching the pigeon move its head) will cause you to see different bursts (or absences) of color, thus giving the pigeon's neck a shifting iridescent effect.
To no one's surprise, the pigeon isn't the master of iridescence. The latticework in its feathers is one of the least organized affairs in bird-dom. Its grid is made up of a thick, jumbled series of filaments. When you see the shimmering on the throat of a pigeon, this is what you're marveling at.
Compare that to the celebrated peacock, which has feathers made up of thin, rigidly-stacked filaments, resulting in more brilliant and dramatic color. Still, it'll be a long time before anyone sees a peacock dash out into traffic to grab someone's discarded french fries.