Who Sees the Best Rainbow
By Steve Roark
Humans are apparently hard-wired to love seeing rainbows, as proven by all the Facebook photo postings that pop up whenever one appears in our area. But have you ever wondered if, say your dog sitting beside you, sees the same rainbow you do? Or how about other animals? Let us delve into color vision by various residents of our planet.
Let’s start with us. A rainbow to us has 6 colors: red, orange, yellow, green, blue, violet. Remember the ROYGBIV memorization trick? Some contend that on really clear days folks with really good vision can see 7 colors, with another shade of violet thrown in (ROYGBIVV). Now back to your dog sitting beside you. His rainbow would start out as blue, then green, a sliver of yellow, and… that’s it. A dog’s rainbow is only half as thick as yours. So he’s sitting there smiling and panting like he’s enjoying it, but in reality he’s thinking “what’s the big deal?”
The difference between us and dogs is that they only have two photo receptors in their eyes, which if you remember from biology, are called cones. They only have blue and green sensitive cones, while we have three including a red one. You wouldn’t think one kind of receptor would make much difference, but three is way, way better than two because it allows a bunch of other colors to become visible. Mix red with blue and you get purple, red with yellow gives you orange, and so on. The additional cone allows us to see about 100 different shades of color, 97 more than your dog can see. He should be envious, but his sitting there licking himself indicates that he could care less.
What about the sparrow flitting around in the tree behind you as you enjoy your rainbow? It varies among bird species, but sparrows can see into the ultraviolet color band and also have more sensitive red cones than we do. Their rainbow would start out extremely red, very red, red, orange, green, blue, violet, and ultraviolet. A much broader rainbow than ours, so perhaps we should be envious of sparrows.
But hold on, what about that swallowtail butterfly feeding on a thistle flower at your feet? Turns out they have 5 kinds of photo receptors, so there’s would be an amazing rainbow with multiple shades of all the colors we see and bunch we don’t. So wow, hats off to butterflies.
This leads up to the question of what animal sees the best rainbow ever? The present champion is the mantis shrimp, which lives on coral reefs with shallow, clear water, and so could, were it so inclined, see a rainbow. These guys have 16 kinds of color receptors, and their rainbow would be unbelievable. They would start out like super-duper ultraviolet, 6 more shades of ultraviolet, then violet, violet-blue, blue, blue-green, green-green, green-blue, bluey-blue, blue, and on it goes until they hit red and blowing our rainbow out of the water.
Of course, our human advantage is that we have the cognitive ability to see and appreciate the beauty of rainbows, even if ours is more diminutive than what is seen by other animals. Still, wouldn’t seeing a 24-layer rainbow be awesome! Information for this article came from a radio program called “Rippin the Rainbow” produced by Radiolab. Look up the podcast online and listen to it, as it’s very entertaining.