Seasonal reproductive success of the Moorhen Gallinula chloropus: the importance of male weight

During a three-year study of 82 pairs of Moorhens Gallinula chloropus, seasonal reproductive success (SRS) varied greatly between pairs. Pairs on big territories had a higher SRS than pairs on small territories, probably because clutch survival was higher on big territories. Pairs that began breeding early had a higher SRS than pairs that began late because early breeders laid larger clutches and could attempt more broods. Pairs with heavy males had bigger territories and began breeding earlier than pairs with light males. Heavy males therefore had a higher SRS than light males. Female weight did not affect territory size, timing of breeding, or female SRS. Assuming SRS to be a good predictor of lifetime reproductive success, selection should favour heavy males but not heavy females. Male Moorhens are significantly heavier than female Moorhens. Finally, pairs with breeding experience had a higher SRS than pairs without, because they had bigger territories and began breeding earlier. However, males in inexperienced pairs were not lighter than males in experienced pairs, so it is not clear why they defended smaller territories or laid later.