First, if you haven’t seen it yet, watch this chicken video. Yes, it’s an ad, but it’s completely worth it.
What are those chickens doing? And more importantly, can you learn to do it in time for your next dance party?
It all has to do with vision. For birds, humans, and any other seeing animal, a problem arises: namely, animals move a lot, but vision works best when the eye is not moving. The receptors in your eye react to changes slowly enough that fast motion of the receptors will blur the image, not unlike how fast panning shots in movies are blurry. Also, it’s easier to see motion—of a yummy mouse running along the ground, say, or a large-fanged predator creeping towards you—if the background is still; and, if you’re moving, it’s easier to calculate how fast you’re going if you don’t have to worry about other, uninformative motion in your vision.
So you have a twitchy animal with eyes that need to stay still. Humans and many other animals handle this with their eyes, by moving the eyes in the opposite direction whenever the head moves. If you focus on a word in this sentence while you move your head from side to side, that word stays in the center of your vision because your eyes automatically compensate for your head movement. This is possible because of the vestibulo-ocular reflex, which uses rotation detectors in your inner ear, and the opto-kinetic reflex, which uses motion detectors in the retina of your eye. And, as you can see, it’s entirely subconscious—and very hard to undo. Just try to keep your eyes still in your head as you slowly turn your head. You can’t (or I can’t, anyway).
Birds can’t do this. Birds have larger eyes for their body size than mammals; owls’ eyes are so big that they had to make them tubular, rather than spherical, just to fit them inside their head! And partly because of this, birds can’t move their eyes very much. So instead, to keep the eyes still while the body moves, birds keep their entire head still.
This makes a lot of sense. If your eyes can’t compensate, the next logical body compartment is the head, and birds’ heads have a large range of motion thanks to their long dinosaur necks.
The chickens in the ad are just doing what is natural to any bird: keeping their heads still while their bodies move in order to have a stable image of whatever they’re looking at. My big question, after watching the ad, was: what are they looking at? They clearly care about it enough to stare, even while a weird camera swoops distractingly all around them. My uneducated guess, based on the final scene where the two rows of chickens face each other, is: another chicken.
So can you learn to do this move? Probably not; it’s as automatic for birds as our compensatory eye movements are to us. But hey, I’m not going to tell you not to try.
Land MF, Nilsson D-E. 2002. Animal Eyes. New York: Oxford University Press.
Just love this general science-y stuff that you post!
Thanks, I’m glad you like it!
Great post, especially as I work in the eye care field :-)
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Great information! We are designing a robot that replicates that movement of the head going up (and down). How do you call this movement? I would love to learn more deeply about it.
all i can say is chicken butt