Many birds can keep their heads absolutely stationary while their bodies move around. (Think, for example, of a hummingbird sipping nectar from a flower while its body moves all around.) This is an adaptation to keep the bird’s perception of the environment constant despite other gyrations of the body (such as the bobbing motion of a walking pigeon). One of my friends called my attention to this YouTube video of the phenomenon, involving a guy holding a chicken. It’s absolutely amazing–so much so that I wanted to try it myself. When I was in North Carolina this weekend, I visited a friend who has a pet chicken, and we tried out this maneuver with the bird. Sure enough, the head remained stationary. I am informed that a reputable journal will soon have a short article about bird head tracking, and I’ll post a linke to it here when it’s published in a month.
Addendum: the same guy demonstrates the phenomenon with a lovely purple martin.