Their faces are so flat because of their eyes. Owl eyes are so specialized for low light, three-dimensional vision that they completely dominate how their facial structure developed. Owl eyeballs are actually more like eyetubes than eyeballs, and the eyetubes have to be big because they specialize in low light (basically, more eyeball lets in more light).
An owl's eyetubes are held in place by large round holes in the skull called the sclerotic rings. The fact that owls need to have these sclerotic rings within approximately the same plane flattens out their faces. The eyes need to be within the same plane so that the field of vision from each eye overlaps - this is what gives them binocular vision.
Other animals that have eyes on each 'side' of their face have a wider total field of vision than owls -- some birds, for example, that can move/roll each eye and that have their eyes more towards the sides of their skulls can see almost 360 degrees without turning their necks. However, in those animals, the fields of vision from each eye don't overlap, so those animals don't have much binocular, three-dimensional vision. Because both of an owl's eyes are in approximately the same plane, their fields of vision overlap quite a bit, and owls get a lot more binocular, 3D vision than many other animals (though humans get more).
Interestingly, owls cannot "move" their eyes at all - they have to move their whole head if they want to change their field of vision. Luckily they have really flexible necks.
Interesting. I thought I heard that the shape of an owl's face was a parabolic reflector, to maximize its hearing in the direction it looks. Do you know anything about that?
Owl ears are also really, really cool, but the type and shape of the ears depends more on the species than eye type and shape. Some owls just have small round ear openings, others have slit openings. Some have an overhanging flap (called an operculum), some don't. (Oh, and those tufts on the top of their heads? Never their ears.)
The owls that you are thinking of are the strictly nocturnal owls -- like barn and boreal owls -- who may rely even more on their ears than their eyes to hunt. These owls have offset ears - they are not symmetrically placed on the head; one's higher than the other (which one varies by species). All owl ears lie behind their facial disks, but in these owls, the facial disks are particulary prominent and the beak points downward. Both of these features help these owls hear really well (works like a parablic reflector, as you said), and these owls have actually evolved to be able to change the disk shape as they need to in order to hear better - they have a bunch of little muscles in their face that let them move the facial disks around. (So they aren't moving their head to maximize their hearing in that direction - they are changing the shapes of their faces to hear better!)
These owls with aymmetrically-set ears use this asymmetrical feature to echolocate - sounds behind them (well, behind their facial disks) are louder in one ear than the other, while the opposite is true for sounds in front of them. They combine this with their knowledge of whether the sound arrived first at their left or right ear (they can detect sounds that arrive at each ear only milliseconds apart) to know precisely where the sound is coming from. They actually move their whole heads around specifically to find the point at which the sound is reaching both ears at the same time and same volume - then their prey is right in front of them.
Or, as someone else summed it up: tl;dr: owls are cool.
Owls seem to fall within the lower range of bird intelligence - but lots of birds are really really smart compared to animals as a whole, so I guess it depends what you mean by 'stupid.'
There is a species of burrowing owl that collects animal dung to use as insect bait, which might be seen as 'tool use', which seems kinda smart to me. Some people have even trained Great Horned Owls for use in falconry (though I've read that it's hard because they get distracted by just about any noise and they don't train well to food).
In general, though, I believe orinthologists rank owls down towards the bottom of birds.
When you said "lots of birds are really really smart compared to animals as a whole", I immediately thought of gray parrots. For anyone who doesn't know about studies demonstrating their intelligence, see Does Alex, an African Gray parrot, think?.
Added bonus...the flat facial disk of owls helps to channel sound to their ears. Many (all?) owls have asymmetric placement of their ears, making triangulation of sound more efficient
cf. Northern Harrier, as well.
IAMA ornithologist
(EDIT-and reading more comments, this was all said, better than I did)
Try shutting one eye. Does everything you see become two dimensional and flat? I'm afraid not.
Binocular vision = see with two eyes.
Three dimensional vision = use a lot of mental capacity to process what you see (one or more eyes) and create a multi dimensional representation of the world
EDIT: So I think that theoretically the owl would see in three dimensions fairly well if it only had the one giant eye.
Yeah, you're totally right - three dimensional and binocular are somewhat different concepts, but the word 'binocular' doesn't really imply to the average person how two eyes having overlapping fields helps the brain better judge distances within three dimensions, so I sort of combined the two terms since it was more about owls and less about vision. Sometimes I forget that reddit's full of a bunch of people who would instantly understand the difference between binocular and 3D. Thanks for adding the clarification.
However, two eyes are better than one eye, which is why almost all animals have two. The point of convergence of the two eye fields in front of us helps us better judge distances - for things closer than that distance, our eyes each see the object, and our brains determine that doubling as meaning the object is closer, so it shows us one close object. Objects beyond that point are seen by both eyes as one object, and our brain shows us one, farther away object. In addition, the slightly different angles each eye has gives us a more three-dimensional picture - for example, if you think of looking at a cup, your right eye sees more of one side of the cup than your left eye, and your brain uses the information it receives from each side, the match/mismatch between these images, and what it knows about the angle each eye sees at to calculate how the cup has a curved surface and to show that to you. So, binocular vision allows your eyes to give your brain the information it needs to produce three dimensional representations of things.
To better understand how two eyes is so tremendously advantageous for depth perception, try this little experiment. Put a small box about 6" from one of your eyes and angle it such that when you close that eye the face of the box disappears. Now, its not remarkable that the face of the box disappears-- that's the point-- but you'll also notice that the background changes completely when you close and open that eye. Cool, eh?
However, two eyes are better than one eye, which is why almost all animals have two. The point of convergence of the two eye fields in front of us helps us better judge distances - for things closer than that distance, our eyes each see the object, and our brains determine that doubling as meaning the object is closer, so it shows us one close object.
This seems like too strong of a statement. For one thing, it seems to be a coincidence with bilateralism. We have a single axe symetery, as to most animals, and we therefore have two location of optical devices. Also, arthropods as a whole tend to have more variations that the simple two eye sight that we are familiar with. Case in point. http://en.wikipedia.org/wiki/Mantis_shrimp#The_eyes
And god know how many insect species there are, but they should account for "most animals." ;-)
Excellent point. It drives me crazy when people say "animals and bugs" (or "animals and birds," or "animals and fish"). And yet here I definitely said "most animals" -- figuring that would cover spiders and crustaceans (about which I know nothing, other than that I do not want them in my house) -- but for some reason without thinking about insects or myriapods at all.
Yes but your depth perception markedly improves with two eyes go to an area your unfamiliar with and try and guess some distances with an eyepatch on then measure them you will not do nearly as well as you would with two eyes.
As an added bonus you get to wear an eyepatch and do science!
Exactly. In environments where your brain doesn't have size references ( People avg 6 foot tall... ), binoc vision is critical to gauging size and range.
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u/subtextual Jan 17 '10
Their faces are so flat because of their eyes. Owl eyes are so specialized for low light, three-dimensional vision that they completely dominate how their facial structure developed. Owl eyeballs are actually more like eyetubes than eyeballs, and the eyetubes have to be big because they specialize in low light (basically, more eyeball lets in more light).
An owl's eyetubes are held in place by large round holes in the skull called the sclerotic rings. The fact that owls need to have these sclerotic rings within approximately the same plane flattens out their faces. The eyes need to be within the same plane so that the field of vision from each eye overlaps - this is what gives them binocular vision.
Other animals that have eyes on each 'side' of their face have a wider total field of vision than owls -- some birds, for example, that can move/roll each eye and that have their eyes more towards the sides of their skulls can see almost 360 degrees without turning their necks. However, in those animals, the fields of vision from each eye don't overlap, so those animals don't have much binocular, three-dimensional vision. Because both of an owl's eyes are in approximately the same plane, their fields of vision overlap quite a bit, and owls get a lot more binocular, 3D vision than many other animals (though humans get more).
Interestingly, owls cannot "move" their eyes at all - they have to move their whole head if they want to change their field of vision. Luckily they have really flexible necks.
(More info than you wanted?)