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Ever wonder what it looks like from a birds-eye-view? Hank explains they see more than you think!

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There are a lot of good reasons to envy birds.  They can fly, obviously, if you're a male you're almost guaranteed to be gorgeous, and they seem to have a knack for meaningful, long-term relationships.  But now scientists are finally beginning to understand what the world looks like through birds' eyes and it's amazing.

We've talked before about how birds can see the earth's magnetic field, but did you know they can also see ultraviolet light?  Us humans, we have three kinds of color receptor cells called cones in our eyes for detecting red, blue, and green.  Birds have four.  That fourth cone lets them see in the ultraviolet part of the spectrum.  And it turns out that most birds that we thought looked pretty boring can actually glow like ravers under the right light.

Example:  The male European Blue Tit is handsome enough under human-visible light, but under UV light its crown of feathers lights up like a Christmas tree.  And it's not just the birds themselves, lots of things reflect UV light; we just can't see it.

A high phosphorous content in urine, for instance, makes it glow vividly in ultraviolet, which is super handy for, like, tracking Meadow Voles if you're a hungry kestrel on the go.  But it's not just magnetic fields and extra colors that makes the bird's eye view of the world amazing.

Birds also have special fovea.  The fovea is the spot in your retina that has the highest resolution.  If you're a human, you only have one in each eye and it's great and all, but it has its limitations.

Try this demonstration.  Just look at me, cover one eye, and then try to read the words on either side of the screen.  It's really hard, and that's because your fovea only covers the middle 40 degrees of your visual field and the greatest concentration of your eyes' cones only covers 10 degrees.  So while you're lookin' at me, you can probably see that all the words are there, but you can't actually focus on them, maybe not even read them.  Once again, birds got us beat.

Birds of prey actually have two foveae in each eye.  This lets their eyes act like cameras that have both a macro lens and a zoom lens.  One fovea can let them focus on objects that are far away, while the other zeroes in on fine details that are directly in front of them.  Seabirds, meanwhile, have a single large fovea that's a strip instead of just a spot.  It runs across their entire retina so the horizon always stays nice and crisp while they fly.

Now here's another demonstration.  Look through a small hole in the middle of a notecard or piece of paper, maybe just do this (02:24).  Focus on a source of light behind that hole, like your computer screen, and then jiggle it around just a little bit.  In a couple seconds, you'll probably start to see the blood vessels in your eyes or, at least, the shadows that your blood vessels are casting on your retina.  Even though the level of light reaching your eye never changes, there are rapid, tiny variations in the direction of that light.  Exactly as might happen to a bird flying under foliage.

When this effect occurs, your entire field of vision can become obscured by the shadows of your blood vessels.  And if you're zoomin' down on a mouse at 80km/hr, it's not a great time for that to happen.  So birds have a unique structure in their eyeball called the pecten oculi, which is chock-full of blood vessels.  This helps give the eye tissues all of the nutrients they need, while reducing the need for blood vessels elsewhere in the eye that would block the retina.  Now that keeps their vision super clear, even in fast-changing light conditions.

So, they can see more colors than us, those colors look brighter, they can see electromagnetic fields, and their eyes have more camera settings than my phone!  Bein' a bird looks pretty good.

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