Why pidgeons bob their heads.

I agree with your theory that pidgeons bob their heads, when walking, in order to maintain balance. It seems to me that if they did so in order to maintain visual focus, they would have to bob their heads when flying as well. What a sight THAT would be!

[Raoul Anatherwan]

Maybe the pigeons have been in the Ghetto for too long...

[Arnold Winkelried]

The column being referred to is Why do pigeons bob their heads? (13-Apr-1979) (http://www.straightdope.com/classics/a1_016.html)