| Abstract: | The purpose of this study was to determine whether parental investment decisions are made on the basis of cumulative past investment or the prospects of expected benefits minus costs. Through clutch size manipulations at nests of Redwinged Blackbirds, Agelaius phaeniceus, we obtained ♂♂ with equal past investment but varying expected benefits. Parental investment was measured by intensity of nest defense against a dummy predator at the nest. Results indicate expected benefits minus costs, rather than cumulative investment, determine parental investment decisions. |
