Mate-feeding has evolved as a compensatory energetic strategy that affects breeding success in birds

In many animals, females are fed by males during courtship or incubation (mate-feeding). According to the mate appraisal hypothesis, females may evaluate the parental capacity of males, whereas the pair bond hypothesis suggests that feeding may strengthen the pair bonds with them. Following the nutrition hypothesis, by contrast, females obtain direct nutritional benefits from being fed by males during periods of high-energy expenditure, such as egg formation and incubation. However, there is little support for these hypotheses at an interspecific level. We tested predictions from these hypotheses in a dataset of 170 species of passerine birds. As predicted by the nutrition hypothesis, we found that mate-feeding has evolved more often in species in which the female incubates and builds the nest alone and have noncarnivorous diets. This suggests that mate-feeding is a behavioral strategy that compensates for nutritional limitations of females during breeding, as both incubation and nest building are energetically costly processes, and noncarnivorous diets are deficient in proteins. We also found that incubation feeding has evolved more often in species that place nests at elevated sites, suggesting that these species face low predation risk that allows males to feed females. In the particular case of incubation feeding, we found that species that have evolved this behavior produce larger clutch size and have higher hatching success. Our results support the nutrition hypothesis from an interspecific perspective, suggesting that mate-feeding is a strategy to compensate for nutritional limitations of females during reproduction and that it has fitness consequences. Copyright 2011, Oxford University Press.