Visual head extension: transitional head coordination in the pigeon squab (Columbia livia).

We describe a previously unreported visuomotor behavior of the developing pigeon squab, which we term "visual head extension." The behavior consists of extension and lowering of the head as the bird descends towards a surface or experiences the optical equivalent of such a descent. A peak in performance occurs 10 days after hatching. Evidence obtained shows that both vestibular and dynamic visual information can independently produce head extension. We go on to place the new behavioral response in the context of a dynamic, relational approach to perceptuomotor coordination, and outline the corresponding advantages of studying the single-limb, head-neck system in the pigeon.