Abstract
Previous studies have linked winter habitat with subsequent breeding phenology and physical condition of migratory birds, but few have found delayed effects of winter habitat on subsequent reproductive success. The aim of this study was to test if African winter habitat is related to subsequent reproductive success of house martins (Delichon urbicum) breeding at a colony in Spain. We measured stable isotope (δ2H, δ13C, δ15N) values from feathers moulted in West Africa and used confirmatory path analysis to test if isotopic values of winter-grown feathers were related to reproductive success through the mediation of breeding phenology and body condition. We conducted separate analyses for males, females and age classes (yearlings vs ≥ 2 years old). Experienced males wintering in habitats of higher rainfall (as inferred from lower feather δ2H values) were in better body condition and produced more offspring during the subsequent breeding season. In contrast, we did not find any effect of winter habitat on reproductive success of young males or females. These findings provide evidence consistent with a complex causal link between winter habitat quality and subsequent breeding success of long-distance migratory songbirds.
Highlights
In an ecological context, carry-over effects occur when the previous history and experience of an individual explains its current performance in a given situation[1]
Confirmatory path analysis showed that rainfall amount as inferred by feather δ2H had a significant direct effect on body condition [estimate (SE) = − 0.33 (0.15), p = 0.04], and that body condition had a significant direct effect on the number of fledglings produced during the breeding season [estimate (SE) = 0.45 (0.16), p = 0.01]
We found direct and indirect effects of environmental conditions experienced in the winter areas on different breeding traits in our migratory study population of house martins
Summary
Carry-over effects occur when the previous history and experience of an individual explains its current performance in a given situation[1]. Few studies have found carry-over effects of environmental conditions from winter areas on final reproductive success[8,9,10,11,12]. Structural Equation Models (hereafter: SEM) and path analysis (a kind of SEM with only measured variables) provide a powerful statistical method to study complex natural systems, since multiple predictor and response variables can be analyzed in a single causal network[19,20] These kinds of analyses can be especially useful in dealing with carry over effects in migratory birds since the above-mentioned variables flow www.nature.com/scientificreports/. The use of path analysis was essential for discerning that arrival, laying and fledging date, as mediated by the effect of winter habitat quality, determined the number of fledglings reared during the subsequent breeding season. We did not detect a final carry-over effect on the number of fledglings produced
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