Imagine a startled pigeon flying at your head. Your eyes—and brain—allow you to see this obstacle quickly, without thinking, and to duck (if you're lucky).
But human eyes, while magnificent, are not the animal kingdom's most impressive. Many types of birds for example can process visual information even faster.
“You can imagine birds flying at relatively high speeds—they have to avoid crashing into tree branches in a millisecond,” says animal ecologist Esteban Fernandez-Juricic from Purdue University.
“Do they see the world in slower motion? We don't know, but that's one of the potential implications,” he says of birds processing images at faster paces.
Birds are rightly famous for their vision, with extremely keen eyes. Hawks, for instance, can spot prey as small as rabbits from three miles away. Sparrows can see ultraviolet waves, revealing a world humans can barely imagine.
In his research with Cornell's Lab of Ornithology, ecologist Rusty Ligonfound that the ability to see UV light influences how some bird species interact in ways that are invisible to humans. The King-of-Saxony's bird-of-paradise, for example, has two long, flowing feathers that are “basically glowing in ultraviolet,” says Ligon.
It's not just birds that see the world in wildly different ways.
Some amphibians, which live their lives within and outside the water, have a three eyelids. In frogs, it's called a nictitating membrane, and it protects their eyes when they're submerged but keeps them moist and clean when they're on land.
“Frogs are believed to be the only vertebrate animals with eyes that can detect color in the dark,” says biologist and National Geographic explorer Jonathan Kolby. With less light, most animals gradually lose this ability, but frogs are nocturnal and can see color even on dark nights with no moonlight.
Animal vision isn't limited to two eyes mounted atop a creature's head.
Earlier this year, scientists discovered that sea stars have eyes at the tips of each of their five arms. They likely see only crude images—what would look to us like roughly 200 pixels according to a study in the journal Proceedings of the Royal Society B—but it's enough to help them make out large structures.
Eyes evolved to be only as complex and energy-intensive as each species needed them to be, biologist Dan-Eric Nilsson told National Geographicin 2016.
“Eyes didn't evolve from poor to perfect. They evolved from performing a few simple tasks perfectly to performing many complex tasks excellently,” he said.