Older is better? Age-related variation in ornamental and breeding traits in bluethroats, Luscinia s. svecica

Abstract

Age-related variation in breeding performance is well-known in birds. Similarly, plumage ornamentation as a signal of male quality may affect breeding performance. However, because of inter-correlation between age and plumage ornamentation, it is difficult to estimate the relative contribution of these factors on breeding performance in natural variation. In the current study, we examined the relationship between breeding characteristics, age and throat ornament size of bluethroat males (Luscinia s. svecica). The study was conducted on 96 males in the Krkonose Mountains, Czech Republic, in 2003-2011. The results show that older males had higher reproductive performance: they arrived earlier, were more likely to be territorial, had larger clutches and thus had more hatchlings. On the other hand, ornamentation had a few, inconsistent correlations with breeding performances: well-ornamented males had fewer mates but had more fledglings. Our results suggest that age rather than ornamentation size is the main correlate of variation in breeding performance.