Every other week, the Outside/In team at NHPR answers a listener question about science and the natural world. This week's question comes from Rob in Archdale, North Carolina.
“Predators have forward facing eyes. Common prey species have eyes on the sides. Is this true? If it is, are there examples in nature where this doesn't hold?”
Host Nate Hegyi looked into it.
Nate Hegyi: Maybe you’ve heard this factoid before. It’s the kind of hard and fast rule that’s taught in an elementary school science classroom. But in case you were sick that day, it also shows up in, uh, more untraditional places.
Joe Rogan: Things that have eyes on the side like a deer, they are looking for BLEEP coming at them. But when something has eyes going forward, it’s looking to attack. Aliens have eyes facing forward, which is interesting.
Nate Hegyi: Joe Rogan. Who I guess knows something I don’t about aliens? Anywhoo… for the most part, this factoid is true. A lot of land-based predators do in fact have forward-facing eyes.
Barb Lake: when you have two eyes in front of your head, you're seeing overlapping vision. So each eye is seeing a little bit on the left and a little bit on the right. And that helps you with depth perception.
Nate Hegyi: This is Barb Lake. She’s a wildlife technician with the Alaska Department of Fish & Game. She says this depth perception helps predators when they hunt.
Barb Lake: It's really great because then you know exactly how far or how close you are to whatever it is that you're stalking or pouncing on.
Nate Hegyi: Meanwhile, a lot of the prey that these predators are pouncing on will have eyes on the sides of their heads. What they lose in depth perception, they gain in a wider field of vision. Which is important if you’re constantly looking for threats.
Barb Lake: So things like horses, it's really great if your head is down and feeding in the grass, you can still see all the way around you to see if that predator is coming.
Nate Hegyi: But don’t hang your hat on this fun fact completely. Because there are a lot of exceptions to the rule… especially when you go underwater. Take sharks.
Barb Lake: Obviously their eyes are on the side of their head and obviously they're predators. So what's up with that? That doesn't make any sense. But if you think of how a shark moves in the ocean, it's very different. So they swim with kind of like a side to side kind of movement. And if your eyes are on the side of your head while your head is moving side to side, inevitably each eye is seeing forward at any time. Whereas for land animals, if you're like a big cat stalking its prey, your head is never moving. It's staying very, very still.
Nate Hegyi: Here’s the other thing - sharks aren’t actually all that concerned with having great eyesight because there isn’t a lot of light underwater. Instead, many marine predators will take advantage of other organs to find their prey.
For example, sharks and fish have lateral lines. These are organs that run the length of their body and sense vibrations in the water.
And then there’s whales and dolphins, whose eyes are also usually on the side of their face. They rely on their spermaceti to find prey.
The spermaceti is the large, bulbous organ you see on, say, the front of a beluga whale’s head. It transmits echolocation, which is like a sonar system.
Barb Lake: So like if you were in the ocean with a sperm whale and it was using its echolocation on you, it could actually see your internal organs. It can kind of be like an MRI with that echolocation.
Nate Hegyi: When you can use sound like that, suddenly vision doesn’t seem all that important.
In fact, maybe we should be more concerned with alien’s big bulbous heads than those forward-facing eyes. Alien echolocation? Pff… no thank you.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.
