How Birds See the World
How Birds See the World
Whether you have a problem with a bird, or just enjoy birds and want to know more about them, it can be useful and enlightening to explore the world form their point of view. The way different birds actually see the world makes a big difference in how they interact with people and our world. Knowing how birds see and interact with the world around them can help us avoid conflicts with birds and better direct our efforts to create a world that is acceptable and beneficial for both birds and people.
First of all, when we’re talking about how birds see the world, we really are interested in how birds see. Birds are very visual creatures. What they see helps determine how they interact with the world around them—including us! In some ways, birds see the world very differently than humans do. It isn’t a stretch to say that they are living in a completely different world when it comes to how much of the world they see and how it looks to them.
Field of View
Humans basically see most of the 180 degrees right in front of us, since our eyes are in the front of our heads. Owls and hawks have similar forward facing eyes, but usually see a bit more of the world around them than we do—from 200-260 degrees. That means they have a much smaller blind spot behind them. Most birds have eyes on the sides of their heads, so they see even more of the world—pigeons see about 320 degrees around them, with only a tiny blind spot behind their head. Ever wonder why it’s hard to sneak up on a pigeon? Now you know! They almost always see you coming. It’s even worse with some ducks like Mallards. Their eyes are so high on the sides of their heads that they actually see 360 degrees—the whole world–around them.
Ever wonder how starlings and other birds can fly in those huge twisting flocks without crashing into each other? Without big blind spots like we have, it is much easier for birds to stay in formation with the other birds around them. Next time you get a chance to watch a bird, notice how much it sees and how that impacts what it does. You will see birds tilt their heads to look up at the sky, and birds pecking at the ground without having to turn their heads to look at the ground—all because their field of view makes this possible for them.
We see about 120 degrees of the world in front of us with both eyes—our binocular vision. With eyes on the sides of their heads, most birds have a much narrower binocular view. Pigeons, with their wide view of the horizon, have only about a 23 degree binocular field of view. Owls may have a 50 degree binocular view—pretty wide for a bird. We use our binocular vision to help us with depth perception (stereopsis). Birds don’t really do this, but just like us, when both eyes are able to look at something it helps them better see faint objects or keep moving objects—especially prey—in their field of view. For Mallards, instead of having a narrow binocular view in front of them, they have a narrow binocular Mohawk strip over the top of their heads—presumably the better to see where they are going or predators that may be above them when they have their bills down in the water!
Most birds have exceptional color vision. Humans distinguish colors based on our color vision cells (cones) having three different color sensitivities. Because the colors we see are based on these three different types of cells, we call that trichromatic vision. Birds on the other hand usually have four different types of cones, with one kind of cone allowing them to see ultraviolet light—making the world a very different place for birds! It is important to remember that birds do not see colors like we do. In fact, birds like crows that all look the same to us, actually look very different to each other—since they can see patches of ultraviolet coloring that allows crows to distinguish males from females and even individual birds from each other. When we have trouble with birds, we need to take this into account. That fake owl that looks really good to us, who knows what it really looks like to a bird! Maybe it doesn’t look so real or scary without whatever ultraviolet coloration normal owls have.
Where we have just one set of cones to help us see greens, many songbirds have two—probably allowing them to make much more subtle differentiations between greens. All the better to spot green caterpillars on green leaves. Birds also have colored oil droplets on their cones, which serve as internal sunglasses to provide different filters for different parts of their world. Pigeons have yellow filters to give them a better view of the sky, just like aviator sunglasses, and red filters of the ground so they can better find seeds to eat on the ground.
Some birds can see polarized light and even magnetic fields. Birds differ from humans in how close they can focus and how much of the world is in focus at any given time. For pigeons, the ground they walk on is constantly in focus—leading them to bob their heads as they walk to freeze their view of the ground as their body moves instead of just having it go streaming by in a blur.
When we watch movies, we know that we are really seeing a rapid series of 24 individual images a second that look like solid moving images to us. If you blink a light faster than 60 times a second (60 Hz), it looks like a steady light to us. Pigeons on the other hand have a “flicker fusion rate” of 100 Hz. Birds of prey have an even higher rate. This allows them to see and respond to things more quickly than we do—like approaching humans, or tree branches flashing past them in flight. A movie of an owl diving on a pigeon would not appear to the bird as a single moving threat, but as a slide show of images. Does that mean birds can distinguish shorter segments of time? Does time itself move at a different speed for them? Some of these differences seriously challenge our ability to even imagine!
So next time you are dealing with a problem bird, or just watching a bird in your yard, watch how it sees and interacts with the world around it. By knowing how much of the world it sees, and how it uses its eyes, you may be able to better understand what it is doing. It may even help you figure out how to keep it from doing something that you is driving you crazy!
Bird Magnetic Compass Vision (Discover Magazine) http://discovermagazine.com/2007/oct/birds-navigate-using-magnetic-compass-vision
Bird Vision (Wikipedia): http://en.wikipedia.org/wiki/Bird_vision
Bird Vision Explained (Purdue University) http://estebanfj.bio.purdue.edu/birdvision/
Color Vision of Birds http://users.mis.net/~pthrush/lighting/cvb.html
the attachments to this post: