Postmating sexual selection in house sparrows: can females estimate good fathers according to their early paternal effort?

Recently, several studies suggested that in species with biparental care, male parental effort (for instance in terms of nest building) serves as a sexual signal to females. In this study on free-living house sparrows Passer domesticus, we investigated how male contribution to parental care varies between breeding stages and whether early parental care of a male reflects his paternal effort in later stages. We found that nest building was performed predominantly by males. However, hatching success was not related to male participation in nest building or early nest guarding. The contribution of males to incubation and chick brooding was lower than in females. Investment in chick feeding did not differ between partners, but varied considerably between males. Only the male effort in chick feeding was related to the number of young at fledging age, suggesting that male assistance is essential to maximise reproductive success in house sparrows. Except for the positive correlation between male nest building and male incubation during egg laying, we found no relationship between early (nest building and nest guarding) and later paternal effort (late incubation, brooding and provisioning rates). Consequently, intensity of male nest building and early nest guarding do not seem to be honest indicators of later paternal effort in the house sparrow. Instead, we speculate that high early paternal effort might be a strategy of some males to manipulate the reproductive effort of their partners.