Reduction of maternal care: a new benefit of multiple mating?

Cost/benefit analyses have been used to understand the evolution of mating by females with multiple males, as in extrapair copulations (EPCs), which are now known to occur commonly in socially monogamous and polygynous birds. Indirect (genetic) benefits have been invoked to explain such mating patterns in some cases, but direct benefits have received less attention. We report a study of direct benefits in the communally rearing Mexican jay (Aphelocoma ultramarina). The social mate of the mother (putative father) is the most reliable feeder of the young in his nest, regardless of cuckoldry. Feedings provided by social fathers are not reduced in relation to their paternity loss. In contrast, mothers having nestlings sired by a second male tend to have lower feeding rates than those without such young. Secondary fathers provided a significantly higher level of feeding to the brood of their female than did (1) random nonbreeders of all ages and both sexes, (2) random male nonbreeders of all ages, and (3) older (2+ years), male nonbreeders. Surprisingly, however, broods with two fathers did not receive a higher level of total feeding, despite our observation that two-father broods had two more helpers, on average, compared to broods without extra fathers. Regardless of age or breeding status, males were more frequent feeders than females. This study provides the first evidence that one of the major costs of reproduction, maternal care of nestlings, is reduced for females that have young sired by secondary males. Copyright 2002.