Head bobbing and the body movement of little egrets (Egretta garzetta) during walking

Although previous studies have indicated that head bobbing of birds is an optokinetic movement, head bobbing can also be controlled by some biomechanical constraints when it occurs during walking. In the present study, the head bobbing, center of gravity, and body movements of little egrets (Egretta garzetta) during walking were examined by determination of the position of the center of gravity using carcasses and by motion analysis of video films of wild egrets during walking. The results showed that the hold phase occurs while the center of gravity is over the supporting foot during the single support phase. In addition, the peak speed of neck extension was coincident with the peak speed of the center of gravity. These movements are similar to those of pigeons, and suggest the presence of biomechanical constraints on the pattern of head bobbing and body movements during walking.