Colossal Orbs of Telescopic Vision
HERE’S AN INTERESTING FACT: birds have far, far better vision than we do, or than any other mammal does. Birds can see colors we can’t even imagine. They see movements that are too fast for our eyes to notice. Their left and right eyes can see different things at the same time! Even scientists don’t yet understand all the amazingness of bird eyeballs.
Part of the reason birds see so much better is they have huge eyes. An eagle or an owl is less than a third of your size but has eyeballs as big as yours. And Eno? Well, Eno has the biggest eyeballs of any animal on land. Let me say that again: ENO HAS THE BIGGEST EYEBALLS OF ANY ANIMAL ON LAND. His eyeballs are bigger than a giraffe’s or even an elephant’s! Only sea giants like whales and colossal squids have bigger eyes.
Bigger eyes mean better vision. But before I explain why, do you understand how eyeballs work? Eyeballs are amazing and intricate and very complicated. But an eyeball is basically just a ball of jelly with a hole at the front and a screen at the back. Light goes in the hole and shows an image of the outside world on the screen. Then special light-gathering information bits inside the screen send all the information about that image to your brain.
As you probably know with televisions, a bigger screen usually has a better image. A giant television screen has so many more pixels—or dots of color and detail—than the teeny TV in your granny’s kitchen, which means a giant screen would show your granny’s cooking shows in way more detail, if she ever bought a new TV.
The same goes for eyes. The huge screens at the back of Eno’s colossal eyeballs have way, way more light-gathering information bits than the small screens in your eyes, which means Eno sees the world in much, much clearer detail than you do. Eno’s eyes can spot the slightest twitch of grass that our eyeballs wouldn’t notice. That might give him a split-second head start that could save his life. And more of those light-gathering information bits also means Eno sees much better in dimmer light at dusk when lions like to hunt.
Now, your teacher will be angry if I don’t tell you the proper words for your eyeball parts. So, the hole at the front is called a pupil. The screen at the back is a retina. The jelly is called vitreous humor—it looks like colorless hair gel. And the light-gathering information bits are called photoreceptors. There are different kinds of photoreceptors that do different things, but we don’t need to worry about that right now.
Bird eyes also have something yours don’t—a strange comb-like lump filled with blood vessels. It’s inside their eyeball, and it’s called a pecten or a pecten oculi, if you want to be fancy. Scientists don’t understand all the amazing things it does, but they know it nourishes the retina. And that means the retina needs fewer blood vessels, so there is room in the retina for even more photoreceptors, for even sharper bird vision. Wow!
Next, Eno’s eyeballs are shaped differently than yours. Your eyeball is rounder at the back, which means the image quickly gets blurry as the retina curves around the sides of your eyeball. But ostrich eyes are flatter at the back, which means the retina is flatter, which means more of the image is in focus, especially at the sides. And that means Eno could read this book just as well if you held it at the side of his head as if you held it straight in front of him.
Hmm . . . ignore that last thing I said. It’s a bad example, and not only because Eno can’t read. Eno’s eyeballs are on the sides of his head—not at the front like yours—so his sideways vision is excellent. (Scientists call sideways vision peripheral vision.) In fact, because his eyes are on the sides, if you held this book right in front of Eno, he might not be able to see it at all. Ostriches can’t see their own beaks!
They can’t even see what they are pecking at the moment they’re pecking it! Crazy! But ostriches can see almost all the way around their heads, which is incredibly helpful when you’re always on the lookout for predators.
And this is still just the beginning of what makes Eno’s eyeballs amazing. Ostriches also have . . .
Look at it go! And look at the gazelles running. That cheetah only needed to twitch and the gazelles were off like lightning, darting and dashing in every direction.
PHEW! The gazelles escaped, this time. A few seconds of high-speed action, then back to the peaceful savanna. It’s so hot here, nobody wants to run for long. But that cheetah looks hungry. I think we should go before the sun sets, don’t you?
ENO IS ONE OF A KIND . . . AND KIND OF WEIRD
THE SAVANNA HAS VARIOUS BIG CATS, like lions, cheetahs, and leopards. There are lots and lots of animals with hooves, like zebras, gazelles, giraffes, and wildebeests. There are doggy creatures, like African wild dogs and hyenas, which aren’t dogs but sort of look like them. But there is only one giant bird on the savanna. Eno is one of a kind.
Another way of saying “one of a kind” is “kind of weird.” Even I can’t argue that ostriches are a strange combination of bits: supersize chicken body, snaky neck, bobble head, no-fly wings, horse legs, horrible toes—and those are just the parts you can see.
But “one of a kind” can also mean “AMAZING! STUPENDOUS! WHIZ-BANG-WOW!” And believe me, with all his weird bits working together, Eno is the fiercest, fastest warrior on the savanna.
There is a lot to explain, so let’s hurry up and meet the family!
HERE’S UMA. BUT LET’S NOT BOTHER HER—she’s sitting on her eggs. She might have as many as twenty eggs under there. Her grayish-brownish feathers really blend in with the dry savanna grasses, don’t they? Eno has other girlfriends (ostriches usually live in smallish herds of a dozen or less), and some of them have laid eggs in the nest, but Uma is his main squeeze. If any of those eggs hatch, it will be Eno and Uma who raise the chicks, no matter who laid them.
Ostriches belong to a strange group of flightless birds called ratites. Most are big and fierce, but none are as big and fierce as ostriches. Rheas and emus look a bit like Uma, but smaller and shaggier, with stumpy legs. Cassowaries look like giant prehistoric turkeys with dinosaur-tooth hats. And then you have the kiwis, which are only chicken-size and very shy.
Not so long ago, much bigger ratites existed. New Zealand had giant moas that were thirteen feet (4 meters) tall! They were hunted to extinction shortly after humans first arrived on the islands, around 600 to 800 years ago. And Mad...