Why pigeons bob their heads...

Cecil's Columns/Staff Reports
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Browsing the archives I ran across this enchanting question right away. To my surprise, this question had developed quite a lot of controversy, with three alternate explanations – none of which agreed with what I think is the best explanation.

The eyes of different animals work in very different ways. This is because they have different priorities. A frog, for example, basically does not see objects that do not move. But if a fly zips by its field of vision, it can focus on it very accurately, discern the fly’s location and zap the fly with its tongue.

The vision of birds works in a similar way. Unmoving objects are not a threat, but moving objects are. Hence, birds see moving objects better. A hawk sees the slight movement of a field mouse from unbelievable distances. A pigeon notices the movement of a predator and takes flight.

In order for the pigeon to notice the movement against the background, it must bob its head when it walks. When its body is moving forward, it moves its head backwards in order to keep it stationary in relation to the ground. Then it brings its head back forward very fast for the next step. This way the background is unmoving for most of the time even with the pigeon walking, and it can easily see motion.

This behaviour is more noticeable in some other birds, especially certain species found on the African savannah. These birds have longer necks, and the bobbing is therefore much more noticeable.

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Hi, and welcome to the SDMB! :smiley: It helps if you include a link to the column in question, so we can all get on the same page, so to speak.

Why do pigeons bob their heads?

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Ooops, peeked at the subject of the sticky message, and erroneously figured that merely mentioning the article would suffice. Thank you for taking the trouble to provide the link and welcome me, all in one breath.

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Much as it distresses me ('cause I was about to let this crackbrained theory have it with both barrels), Daliden is right. While looking for data to back my position (something you might consider, Daliden), I found this:

I then searched for this Dr. Frost, and found his Website:

[quote]
Frost, B.J. The optokinetic basis of headbobbing in the pigeon. Journal of Experimental Biology, 1978, 74, 187-195.

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I must confess that I did not search for sources to back me up. I do have an excuse, however: I believed that if any sources had existed, they would already have been quoted.

I now realize that the original pigeon question dates to a time when searching for information was not quite as easy as now.

I promise to back up my opinion better, if I happen to come across a subject I believe I know anything about. It might take a while, though.

Thanks for doing my research for me :smiley:

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the pidgeon bobs its head because it is a groovy little city rat, keepin’ the 70’s and 80’s alive for every wandering urbanite.

a.

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I think this doesnt go far enough in explining why they bob. Pigeons also jerk and bob their heads when sitting still. I thik they do this to basically fix a point in 3 dimensions. Particularly i imagine when something moves into its vision it bobs its head to get a second read on the object to triangulate its position.

If you watch a pigeon come up and take a seed up off the ground or from your hand it never just walks up and scoops it. It stops cocks one eye toward the seed, jerks/bobs its head to a new position while still looking at the seed then will quickly dart its head forward and grab the seed. Anyone who has fed them by hand can tell you that they are really accurate and can take a small seed from your palm very quickly and touch ONLY the seed.

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albatross37: wrote::
Member

Registered: Jul 2002
Location: japan
Posts: 19
the pidgeon bobs its head because it is a groovy little city rat, keepin’ the 70’s and 80’s alive for every
wandering urbanite

END OF THAT albatross37 cats’ write’n::

Very close to the truth. The stories about the eyesight are very interesting, funny how man looks at other things throught their own eyes.

The real reason they bob that little head back and forth, as stated, even while sitting, is due the ansestory of the Pigeon.

Long long ago, back before the domestication of the Pigeon, they were a simple migratory bird that was real fast food, for it’s time. The routes the pigeon would take in it’s yearly migrations would take it from it’s prefered home, to feeding grounds to the north in the northern summer. The cool bobbing motion they have is inherant of the continent. Like Austrailia has pouches in all the mammals, African spiecis’ have great abilities to perform dances for the prospective mate durring that “season”. Therefore the pigeon is just dancin along, groovin’ with the beat of everyday life in the city.

It seems funny to me, knowing that the common Pigeon was brought to the new world by European settlers as a reliable source for food, and most people look at them as city rats with wings.

(the above is written with a party time-joking attitude, please do not take offence at the above in anyway, it is not meant to be offensive)

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Because they can :wink:

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Over here in St. Petersburg there is a really neat bird called the hooded crow. It is bigger than a pigeon, and its legs are much longer and set further apart, so that when it walks it looks a bit like a reptile (making me visualize the dinosaur to bird idea).

It also bobs its head, but in very slow motion compared to a pigeon, since it takes fewer, longer steps. Watching them, I thought about the weight distribution during the step cycle, and saw that if it did not bob its head, its ass would bounce. When it stands, its weight is generally balanced fore and aft of the line between its feet. When it moves one foot forward, though, a majority of the weight is aft of the new line between its feet. and so it would tip backwards, unless it counters by extending its head.

Dr. Frost’s website would not load for me, but offhand I can think of one possible drawback in his treadmill experiment: if a pigeon is on a small treadmill. it is not moving its mass, it is only moving the smaller mass of the treadmill. That might make it easier for the pigeon to find a pace and shorter step that would keep the variations of weight distribution down, so it wouldn’t need to bob.

Further, when the hooded crow walks fast, it skips rather than walks (sort of the way Popeye would run in the original Fleischer black and whites) and does not bob, because the distance between its feet when they touch the ground is short compared to the distance covered in the air. Did Dr. Frost look at different gaits (if such exist in pigeons)? JDM

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Here you will find an except from a favourite radio show of mine, which explains the reason why pigeons bob.

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With reference to the very good book “How the mind works” by
Stephen Pinker. Pigeons bob there heads in a way that cancels out the jerky movements of their walk so that they don’t see everything jerking backwards and forwards when they walk, they see a smooth image of the world around them. The idea that this is to enble pigeons to have depth perception is wrong, you try closing one eye and jerking you head backwards and forwards see if that helps give depth perception, I think not.

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maccer, to us humans, who are used to getting our information stereoscopically, the idea of getting this information from one eye seems strange. But perhaps a pigeon’s brain, among that of other creatures whose eyes reside on the sides of their heads, can assemble a three-dimensional picture from two closely spaced two-dimensional ones. When you close one eye, and move your head side to side in a line (not just turning your head, that doesn’t work as well), the objects closest to you appear to move more than those farther away. The pigeon’s brain then could use that information to decide how far away something is. It could do this automatically, not generating a actual three-dimensional picture, but determining the distances all the same. In the few minutes I experimented, I feel that I could learn to discern relative distances, however roughly, given time and training, with only one eye. I am not an ornithologist, so I may be completely wrong, and it may have to do with weight redistribution while walking. But my logic tells me that pigeons jerk their heads to see properly.

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So I was around some pigeons recently, and I couldn’t help but think of this thread. I think everyone’s partially right. Here’s my “unified theory” of pigeon bobbing, followed by an interesting corollary and an additional (maybe confounding) tidbit.

Unified Theory

In everyday life, the pigeon “snaps” its head to a new fixed spot in space with every step. For a few hundredths of a second, everything’s a blur, then for maybe a tenth of a second it can take a nice “snapshot” of the surroundings. During that time, it can look for motion against the unmoving background, checking for approaching predators. In addition, after it’s taken a few snapshots, it can assemble a 3-D, nearly-360-degree picture, since its eyes are on the sides of its head.

When the pigeon is stationary, it must still perform the head-bob to create the snapshots necessary for the 3-D picture of the food it’s after.

This head motion does seem to offset the backward motion of the legs somewhat. If it didn’t help at least a little, then there’d be no reason (that I can think of) for the bobbing to synch up with the footsteps. But whether the “balance thing” or the “vision thing” came first, I don’t know. The treadmill test suggests that the vision thing is more important, since the bobbing stops when the whole bird is fixed in space (stationary bird on moving treadmill).

Interesting Corollary

There’s an interesting consequence of the “vision+balance” dual-purpose head-bob. It implies that a bird’s neck and leg lengths should typically be proportional, across species. The neck length should be about the length of one pace. For the balance thing, you need to bob once per step. For the vision thing, you need to shoot your head forward one pace, then draw it back to keep it fixed in space as you take the step. Thinking about pigeons, roadrunners (the real kind), and flamingos, they seem to fit the hypothesis. I don’t know if roadrunners bob; I think flamingos do.

Confounding Tidbit

Along with the other pigeons was a one-legged pigeon. With a two-legged pigeon, the body motion is pretty smooth, while the head jerks. For the one-legged pigeon, a smooth body motion was out of the question. So he was hopping, and the body was jerking around pretty fierce. But the head seemed to be moving smoothly – not snapping from one fixed point to another, but rather gliding smoothly along.

Maybe I wasn’t paying close attention, and the head was taking its snapshots in-between hops (as the whole body was mostly stationary preparing for the next hop), then snapping the head to the new spot during each jerky hop (when it would be very hard to keep it fixed in space anyway). But if the head motion was really smooth, then I’m not sure what it says about my two-legged uber-explanation.

Any further thoughts are welcome.