The development of behavior

Abstract

A full understanding of behaviour requires a knowledge of the processes whereby, under normal circumstances, a fertilized egg develops into an adult animal with a complete behavioural repertoire. For example, closely related passerine birds sing songs which vary in overall pitch, in the pattern of sounds involved and in their degree of complexity. Species also vary in the number of song types they sing; a chaffinch (Fringilla coelebs) has just one song type, a marsh wren (Cistothorus palustris) may use upwards of one hundred song types, while sedge warblers (Acrocephalus shoenebaenus) produce ‘… a seemingly endless stream of constantly varying song types’. (Catchpole, 1979.) Individual birds may produce variations on their species specific theme in the form of local dialects (Marler and Tamura, 1962) and may have repertoires of different sizes (Catchpole, 1979). What sorts of process could account for the development of behaviour patterns like this which are at once sufficiently constant to be a recognizable attribute of the species concerned and yet which vary between individual animals?