I can't say that I have, now, pigeons do bob their heads naturally when walking, that's called saccadic head movement, which is similar to our saccadic eye movement, it's to stabilize our view and help focusing on the important stuff
I feel like Freud's name is most famous/well known, but Skinner discovered so much about behavior and a lot of his theories and findings are used today. The entire field of behavioral analysis is a direct result of him.
Those poor pigeons gonna need their medications