Head movements and eye functions of birds.

The forward and apparent backward movements of the head which pigeons, chickens, and certain other fowls display while walking have been commented on by various persons orally, but seldom in print. In general, it seems to be assumed that these movements result, more or less incidentally, from the act of walking itself, being somewhat comparable to the swinging of the arms of a human being or the flopping of the ears of a mule. But this, we shall see, is an erroneous supposition. To the casual observer it also appears that as a chicken or pigeon walks along the head is moved forward, allowed to go backward somewhat, and then thrust forward again; even after some rather careful observations, the senior author still retained the impression that the pigeon's head moved back slightly. Martin A. Mikesh contended that the backward movement is illusory, that the fowl's head goes forward only, and that during the apparent backward movement the head is really at rest. But so far as we know, no crucial photographic study, which would permit a definite analysis of this point, has ever been previously attempted. In view of its bearing upon the general problems of vision, equilibrium, and vestibular functions, in addition to its intrinsic interest, the problem seemed to be of sufficient importance to warrant making a series of motion pictures of certain birds during pedestrial locomotion and of their reactions to certain passive bodily movements. Thus far, the study has been restricted to pigeons, chickens, starlings, and ducks; but sufficient data have been obtained to prove that the apparent backward movements of the