THE DISPLAYS GIVEN BY PASSERINES IN COURTSHIP AND REPRODUCTIVE FIGHTING: A REVIEW

Summary. The components of the displays of passerine courtship fall into at least seven major groups: those of sexual, aggressive, fear, alert, nesting, parental and begging responses. All may occur also during reproductive fighting. However, in order to present the observational data reviewed here it was necessary to classify display components on form alone. In each case distribution through the passerines, and possible origin and homologies, are discussed. The categories used were:– Bill raising. This is characteristic of male courtship and reproductive fighting displays in many groups, but usually only occurs in one of the two contexts in any particular species. There is evidence that it may sometimes be homologous in both contexts. Bill lowering. Most groups possess this component. Its most common origin is probably from lowering the bill to pick up or insert nest material. Wing vibration. In some groups the wing vibration of male courtship appears to be homologous with that of the female precopulatory display, in others with that given when begging for food. Feather raising. One of the main sources for the feather raisings of displays appears to be feather raisings normally given in response to thermal stimuli. Components of the head‐forward posture. This posture and that of begging have nearly all their components in common. Possible homologies between them are discussed. Lateral asymmetry. Lateral tilting of the body together with turning of the tail appear to be almost confined to the Carduelinae, Fringilla and the Estrildinae. Components of the female precopulatory display. The passerines can be divided into two groups according to the presence or absence of vertical tail vibration in the female precopulatory display. Song. Passerine song is best regarded as derived from contact calls. It still retains much of the same motivation and is similarly facilitated by androgens. The two extreme conditions (which are connected by all intermediates) within the passerines are those species in which the male sings only when alone and those in which there is so rigid an association between courtship displays (usually a bow) and song that males display even when singing alone. Systematic implications of the distribution of these different components are discussed. It seems likely that the Estrildinae and Ploceinae form a natural group which may be related to the Corvid assemblage. A number of other relationships are suggested, but the data do not allow any firm conclusions.