Wing characteristics and spring arrival date in Barn Swallows Hirundo rustica
Flight morphology traits affect flight performance and energetic demands, and hence they are of special importance for migratory birds. It is believed that high wing aspect ratio (ratio of wing span squared to wing area) and low wing loading (ratio of body weight to wing area) both reduce the energetic costs of flight, thus allowing for enduring flight and fast migration. We addressed this topic in a four-year study on the Barn Swallow Hirundo rustica population near Warsaw, Central Poland. We hypothesized that individuals possessing wings with higher aspect ratio and lower loading should arrive at the breeding area earlier than other individuals, and that these individuals should be characterized by higher annual survival than the average individual. Male Barn Swallows arrived at the breeding ground on average earlier than females, and older birds arrived earlier than second year birds. Males with high aspect ratio wings arrived from Africa earlier than the average male, independent of age. There was no significant association between aspect ratio and arrival date in females. The relationship between male wing aspect ratio and arrival date remained significant when controlling for the effects of potential confounding variables (including the estimates of male phenotypic quality, body condition and body size). High aspect ratio wings may help male Barn Swallows migrate faster than the average male, and thus arrive at the breeding area earlier in spring and achieve the benefits of early arrival. However, the relationship was weak, explaining only 5% of the variation in male arrival date (age, and hence experience, explained 38% of the variance). Wing loading was significantly correlated with timing of arrival in both male and female Barn Swallows, with early arrivals being characterized by higher wing loading than later ones. This finding can be explained by the benefits of arrival at the breeding quarters with body reserves that should help copy with costs of early arrival. We found no significant relationship between wing area and timing of arrival. Furthermore, we found no evidence for wing aspect ratio and wing loading determining annual survival rate in the Barn Swallow.
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Document Type: Research Article
Publication date: June 1, 2013