Courtship-feeding and clutch size in Common terns Sterna hirundo

Two of David Lack’s most original and important contributions to the study of breeding biology in birds were his discussions of the significance of courtship-feeding (Lack, 1940) and the determination of clutch size (Lack, 1947). He originally argued in general terms that clutch size is adjusted, through the action of natural selection, to correspond to the maximum number of young that the parents can raise successfully (Lack, 1954). However, he agreed in his later writings that in some species clutch size may be limited below this optimum number by the nutritional reserves available to the female at the time of laying (Lack, 1963; 1966; 1968). If the nutritional state of the female is indeed limiting in this way, the phenomenon of courtship-feeding takes on special significance, because the food provided by the male may contribute directly to the reserves required for egg laying (Lack, 1966 p. 23; 1968 p. 287). There is now evidence in several species that courtship-feeding contributes significantly to the nutritional intake of the laying female (Royama, 1966; Brown, 1967; Krebs, 1970; Nisbet, 1973). This paper reports recent observations of the relationships between courtship-feeding, clutch size, egg size, and the weight of laying females in Common terns Sterna hirundo.