Agonistic Behavior and Territory in the American Redstart

Abstract

A few essential terms are reviewed. Agonistic behavior concerned with attack and escape. Individual distance is an area around a bird, which moves with it, has no topographical reference, and into which no other individual allowed to come (Conder, 1949). Displays are defined by Moynihan (1955) as those peculiarly standardized and often exaggerated performances, including all vocalizations and many movements and postures, which have become specialized and modified as social signals or releasers. Blest (1961) describes ritualization as evolutionary process responsible for the existence of interand intra-specific signalling movements. Intention movements are the incomplete and low intensity movements, so called by Heinroth because they reveal what the animal 'intending to do' . (Marler, 1956). Tendency used here in the sense of Hinde given by Marler (1956) as the readiness to show a particular type of behaviour as observed under natural conditions. The strengths of the attack and escape tendencies are determined by using the methods described by Tinbergen (1959). The first method involves recording what behavior follows a given display if the stimulus situation (i.e., the other bird) remains constant. This method requires many observations of the same display since the stimulus situation often varies in natural encounters. If a display leads to attack 70 per cent of the time and to escape 30 per cent, it can be said that this display caused by a relatively strong attack tendency in conflict with a weaker escape tendency. Another method involves an analysis of the situations in which the display occurs and frequently used in this study in combination with the first method. The least reliable method consists of analyzing the form of the display. For instance, if it consists mainly of intention movements to fly from the opponent, one can postulate that it reflects a strong escape tendency. The function of a display determined by observing the response of the other bird (Tinbergen, 1959). For example, if a certain display by one bird typically causes the second bird to flee or to cease an approach, the display has a threat function.