Maternal Condition and Nestling Sex Ratio in House Wrens

Abstract

Abstract Parents are expected to vary the sex ratio of their offspring in relation to the sex-specific fitness benefits. However, benefits of producing sex-biased broods may be dependent on condition of the female. For example, mothers in good condition could achieve greater fitness if they produced high-quality sons, whereas, mothers in poor condition would gain more by producing daughters rather than poor-quality sons. As a consequence, we would expect to see a relationship between female condition and sex ratio of offspring. We examined effect of maternal condition on nestling condition and sex ratio in the House Wren (Troglodytes aedon). Overall sex ratio of nestlings in the population was not biased, but females in better condition produced relatively more sons. Overall positive relationship between female condition and proportion of male offspring was due to second broods, which were significantly male-biased and more likely to be produced by females in good condition. Females in better condition also tended to provision young more often and produced both male and female nestlings in better condition. Polygyny and extrapair mating are common in House Wrens. If males in good condition are more likely to be successful breeders as adults, then it may benefit mothers in good condition to produce more sons.