Recently, I’ve started to wonder why pigeons bob their heads in such a violent manner when they walk. This habit seems like it consumes a lot of calories… don’t they need every bit of energy in order to fly? I don’t understand why natural selection hasn’t bred pigeons that walk without bobbing their heads. Wouldn’t they be more efficient and therefore more fit?
Here are some hypotheses I’m toying with to explain this behavior:
Maybe this actually is the most efficient way for pigeons to walk. Perhaps they’re counterbalancing themselves the way a cat does with its tail.
But, if pigeons bob their heads when they’re standing still, this hypothesis wouldn’t explain why they do that. I haven’t been able to watch pigeons standing still long enough to see if they continue to bob their heads, though. (And even if they do, I guess it could be an instinct that’s only useful when they’re walking, but it’s too ingrained for them to stop when they’re just standing around…)
Because they’re not predators, pigeons’ eyes are set far apart on their heads. This gives them a wide field of view which helps them to see approaching hawks. As a side effect, their binocular vision is quite narrow (anyone know how narrow?). This means that both of their eyes can only focus on objects directly in front of them. Objects that are slightly off to the side can only be viewed by one eye, impairing depth perception.
I was standing on the sidewalk one day watching a pigeon bob its head when I decided to close one eye and see how my depth perception was affected. I still had to focus my eye’s lens to see an object clearly, so my depth perception wasn’t completely gone, but it was greatly diminished. Then I tried to mimic the pigeon. If I bobbed my head towards the object and then away, I got a better sense of how far away that object was. Closer objects appeared to get bigger when I bobbed towards them, while objects farther away didn’t.
(Now that I think about it, I probably looked a little odd doing that…)
Anyway, maybe pigeons are compensating for their poor binocular vision in a similar manner. Their quick motions could be an attempt to gauge the distance to the nearest scrap of food so they can accurately peck at it.
Does anyone have a better idea?
Update: Dae presented video evidence of a more compelling explanation.Last modified February 6th, 2012