Abstract
Environmental conditions encountered by migratory seabirds in their wintering areas can shape their fitness. However, the underlying physiological mechanisms remain largely unknown as birds are relatively inaccessible during winter. To assess physiological condition during this period, we measured corticosterone concentrations in winter-grown primary feathers of female great skuas (Stercorarius skua) from three breeding colonies (Bjørnøya, Iceland, Shetland) with wintering areas identified from characteristic stable isotope signatures. We subsequently compared winter feather corticosterone levels between three wintering areas (Africa, Europe and America). Among females breeding in 2009, we found significant differences in feather corticosterone levels between wintering areas. Surprisingly, levels were significantly higher in Africa despite seemingly better local ecological factors (based on lower foraging effort). Moreover, contrary to our predictions, females sharing the same wintering grounds showed significant differences in feather corticosterone levels depending on their colony of origin suggesting that some skuas could be using suboptimal wintering areas. Among females wintering in Africa, Shetland females showed feather corticosterone levels on average 22% lower than Bjørnøya and Iceland females. Finally, the lack of significant relationships between winter feather corticosterone levels and any of the breeding phenology traits does not support the hypothesis of potential carry-over effects of winter feather corticosterone. Yet, the fitness consequences of elevated feather corticosterone levels remain to be determined.
Highlights
Most seabirds breeding in temperate and Arctic regions are migratory [1] and spend most of the year away from their breeding colonies [2,3]
While there was no effect of breeding colony (GLM, F2,86 = 2.48, p = 0.09), wintering area significantly influenced feather CORT (GLM, F2,86 = 3.92, p = 0.02) which was significantly higher in Africa compared to America (28.8961.75 pg/mm versus 22.1461.65, respectively; Tukey’s HSD post hoc test, p = 0.02), Europe being intermediate at 25.5561.55 pg/mm (Tukey’s HSD post hoc tests: Europe/America: p = 0.31; Europe/ Africa: p = 0.32)
As indicated by the significant interaction between breeding colony and winter area (GLM, F3,86 = 5.15, p = 0.002), feather CORT did not vary consistently among colonies; Shetland birds that spent the winter in Africa showed the lowest feather CORT levels while birds from Iceland and Bjørnøya exhibited their highest levels whenever wintering in Africa compared to other areas (Table 1; Figure 1)
Summary
Most seabirds breeding in temperate and Arctic regions are migratory [1] and spend most of the year away from their breeding colonies [2,3]. High feather corticosterone levels on wintering areas were attributed to stressful conditions and population declines in European trans-Saharan migrant Egyptian vultures (Neophron percnopterus; [12]) and were negative predictors of future survival in wild house sparrows (Passer domesticus; [13]). The latter studies reported negative effects of elevated feather CORT levels on survival probabilities, they did not report effects on reproduction during the breeding season. While feather CORT levels assessed in puffins were measured during the course of winter, no specific winter areas were identified
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