Theory of intraspecific nest parasitism in birds

Abstract

Abstract. The evolution of intraspecific nest parasitism is affected by egg recognition ability and clutch size. The coevolution of these three traits was analysed theoretically using a quantitative genetic model. Both multiple-nest parasites, which lay parasitic eggs in the nests of many hosts, and single-nest parasites, which lay in the nest of a single host, were analysed. The model predicts the following. (1) Brood parasitism evolves when the competition intensity among offspring in a nest, s, is larger than the parasitism cost, n. (2) The optimal parasitism rate, p* , the optimal recognition rate, r*, and the optimal clutch size, E*, increase with s/n. (3) r* , p* and E* are larger for multiple-nest parasites than for single-nest parasites. (4) The number of eggs laid in a female's nest is the same as the optimal clutch size without parasitism, Ê. (5) The optimal clutch size, E*, and the sum of the nest owner's eggs and the parasitic eggs in a nest, i.e. (1 - p*)E* + (l - r* )p*E*, are larger than Ê .