Factors governing the changes in strength of a partially inborn response, as shown by the mobbing behaviour of the chaffinch (Fringilla coelebs) - I. The nature of the response, and an examination of its course

Abstract

The 'chink' call given by chaffinches to non-flying predators can be used as an index of the intensity of the response. The response to predators thus provides suitable material for the quantitative study of certain aspects of instinctive behaviour. Before quantitative treatment can be attempted, however, a qualitative survey of the nature of the response is necessary. This paper contains such a survey, followed by an examination of the course of the response. The 'mobbing' response given to predators depends primarily on a conflict between tendencies to approach the predator and to flee from it; an investigatory response also plays a role. The movements made in mobbing are very similar to the intention movements of taking flight. Comparative study shows that the precise nature of the movements varies with the systematic position of the species concerned. The characters of owls which are important in the release of the mobbing response are analyzed. The recognition of many of these characters, including that of shape, seems to be inborn. The motor pattern of the response is also inborn. The behaviour does not appear until the bird is several weeks old: the nature of the maturation process is complex, and involves changes on both sensory and motor sides. The course of the response is described. Various characters of the response are selected for study, their variability examined, and some of the factors which control them investigated. Some of these characters vary independently of each other, so the features of the nervous mechanisms on which they depend must also be independently variable.