Why do birds move their heads back and forth while walking?

Like I've mentioned a couple of times earlier, there are amazing things around us, wonderful science to learn from, if only we cared enough to ask the right questions. This was one such question I asked recently. There are a good number of birds here at IITM so a while back, I was looking at them as they were walking on the ground. And while they were walking, all of them were moving their head back and forth. Well, at least at the time it looked like that, as though they were moving their head with every other step they took on the ground. I asked friends of mine who were around at the time why they thought birds did so and they guessed that balancing themselves had something to do with it. I asked an ecologist friend of mine if she knew the answer and when she didn't know the answer, I gave up looking for the answer.

I noticed this again yesterday and I realized that I could've asked the internet the same question. So I did. Apparently, I was looking at it wrong apparently. It wasn't that the birds were moving their heads as they were walking, it was that the bird's heads were remaining still as their body moved.

So, unlike us, birds apparently have a tough time focusing and keeping track of things while they are moving. We can move our pupils and eye balls while walking to track things but the birds can't. So, instead, they move their body while trying to keep their head in the same place and then all of a sudden, they move their head to a new position and move their body again. Just watch this youtube video of a chicken being moved around while it's head remains in the same position. Maybe that'll help you understand what's happening.

You can also read this wired article or reddit thread. Hope you learnt something new today because I did.