The Motivational Organisation Controlling the Mobbing Calls of the Blackbird (Turdus Mer Ula) Iv. a General Discussion of the Calls of the Blackbird and Certain Other Passerines

Abstract

AbstractI. All the main vocalisations of the Blackbird (excluding song) have as one of their causes the presence of a frightening object. The alarm call 'seee' may depend on the same action potential as the 'duck' group of calls. The causation of mobbing calls given in subsong is discussed. 2. The motivational organisation underlying the mobbing calls is such that they (or their variants) occur adaptively in a number of quite different contexts (e.,g. mobbing, fledgling location calls) and also in a context (reproductive fighting) where they are probably not adaptive. 3. Two Buntings (Emberiza spp.) have calls which are apparently motivated in the same way as the 'duck' group of calls. In one of them, the general threshold for calling appears to be permanently high in the adult. 4. The motivation of behaviour by a 'conflict of drives' is discussed. A simple behaviour pattern which genuinely depends on the interaction of two systems controlling groups of acts may be caused in two different ways. It may depend on the summation of positive effects from both systems. Alternatively it may depend on only one of the systems, but occur only when other systems are competing with it for control of effectors, so that the action potential for the behaviour pattern rises unusually high. The theoretical consequences of such competition (which can be represented by a variable of the general threshold type) are discussed; they appear not to have been fully recognised previously. Evidence is given that such interactions affect behaviour other than vocalisations.