A note on the evolution of clutch size in altricial birds

David Lack (1947; 1954) suggested that clutch size in birds is adapted to correspond to the maximum number of young that parents can nourish. The studies that Lack’s pioneering work stimulated have revealed both supporting and contrary evidence (see Lack, 1954, 1966; Wynne-Edwards, 1962; Skutch, 1949; 1967; Klomp, 1970; Hussell, 1972). Lack’s hypothesis also has been criticised on theoretical grounds. Skutch (1949) suggested that predation could determine optimum clutch size if the loss of nests to predators were to increase as brood size increases, hence as feeding visits, begging and general activity about the nest increase. As Lack (1949) pointed out in response, whether predation or starvation is the principal cause of death, the optimum brood size is none the less that which produces the most young on average.