The influence of sex and body size on nestling survival and recruitment in the house sparrow

Differences in the survival rates of males and females over the period from hatching to recruitment can have important impacts on individual fitness and population demographics. However, whilst the influence of an individual's sex on nestling growth and survival has been well studied, less is known about sex-specific survival over the period between fledging and recruitment. Here, we analyse nestling survival and recruitment in an isolated, island population of house sparrows (Passer domesticus), using data collected over a 4-year period. Nestlings that had a greater mass at 1 day old were more likely to fledge. Recruitment was also positively associated with day 11 mass. The positive influence of nestling mass on survival to fledging also increased as brood size increased. There was no difference in the survival of male and female individuals prior to fledging. In contrast, over the period from fledging to recruitment, females had significantly less mortality than males. Recruitment was also positively associated with 11-day-old mass. Neither the nestling sex ratio nor the fledging sex ratio deviated from 0.5, but the sex ratio amongst recruits was female biased. Our study shows that sex can influence juvenile survival, but also shows that its effect varies between different life-history stages; therefore, these stages should be considered separately if we want to understand at what point sex-specific differences in juvenile survival occur. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 680-688.