On Locomotory Movements in Birds and the Intention Movements Derived From Them

This paper is intended to show that a great number of movements in birds, the origin of which has not hitherto been understood, are intention movements or movements derived from them. Pure intention movements (HEINROTH, 1910) being low intensity forms of innate behaviour patterns, are as a rule, the very first parts of an activity. Because many instinctive acts begin with a locomotory movement towards something (food, or a mate, or an enemy) most intention movements are low intensity forms of locomotion. In order to recognise pure intention movements therefore it is necessary to study the form of locomotory movements first. This is done in Chapter II, in which special attention is given to hopping and walking. It is shown that hopping involves not only the feet, but also movements of the body, the neck, the wings and the tail. Walking is "one-sided hopping", in which both feet are used alternately, and in which each foot is supported by body, neck, tail and wing movements. Chapter III discusses a number of intention movements. Chapter IV shows that the majority of intention movements are difficult to recognize because they have undergone a secondary evolutionary change (ritualisation) as an adaptation to a newly acquired function, that of acting as a social releaser. Comparison enables us to trace a number of principles involved in this secondary change, viz.: (1) exaggeration, (2) a shifting of thresholds of the component elements. and (3) loss of coordination between the component rhythms. Applying these principles, many so-called display, threat and begging movements can be understood as ritualised intention movements. Owing to the extreme scarcity of accurate comparative studies it is, in most cases, not possible to do more than make a guess as to the origin of a given movement. And although the available facts for the relatively better known groups such as the pigeons, ducks, and the Gallinaceous birds, support my relatively speculative conclusions, I should like to emphasize the need of accurate comparative studies aimed at a tracing of the origin of derived movements.