The growth bars on tail feathers in the male Styan's Grasshopper Warbler may indicate quality

Abstract

We propose that growth bar size may indicate the quality of individuals in Styan's Grasshopper Warblers Locustella pleskei. Positive correlations of an individual's standardized growth bar width between years showed that some individuals of both sexes were usually in better condition than others. The survival rate of males with wider growth bars was higher than that of other males. These survivors might have survived better because of a better body condition. We also examined the relationships between growth bar width and reproductive parameters (arrival date, pairing date and reproductive success). Males with wider growth bars arrived earlier, acquired a mate earlier and achieved higher total reproductive success by breeding twice. In females, growth bar width was correlated with reproductive parameters (arrival date, pairing date and total reproductive success), but not with survival. These results suggest that males with wider growth bars were of higher quality than those with narrower bars. The contrasting results for the two sexes may be explained by differences in their breeding tactics.