Sex and migratory strategy influence corticosterone levels in winter-grown feathers, with positive breeding effects in a migratory pelagic seabird
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To overcome unpredictable stressful transitory events, animals trigger an allostatic response involving the hypothalamic–pituitary–adrenal cortex. This hormonal response, which involves the release of glucocorticoids which in turn mediate between the main physiological mechanisms that regulate the energetic demands and resource allocation trade-off with behavioural responses to environmental perturbations and may ultimately lead to variation in fitness. We have used the Cory’s shearwater Calonectris borealis, a sexually dimorphic pelagic seabird with a partial migratory strategy, as a model bird species to analyse a number of traits related to the stress response. We investigated whether the activation of a stressful response, mediated by corticosterone, during the wintering period (1) correlated with the previous breeding success, (2) was affected by the migratory behaviour of male birds and (3) had consequences in the fitness of the birds. Corticosterone levels in feathers grown overwinter were analysed in 61 adult birds during three consecutive migratory periods (2009–2012) and in 14 immature birds in the wintering period 2010–2011. Moreover, the levels of corticosterone were analysed in experimental birds which were freed from their reproductive duties and compared with control birds which raised fledglings to the end of the breeding period. The results show that the levels of corticosterone were sex dependent, differed between years and were affected by the migratory strategy performed by the birds. The activation of the stressful response over the wintering period generated residual carry-over effects that positively affected the reproductive output in the subsequent breeding stage, a phenomenon previously undescribed in a long-lived pelagic seabird. Our study provides evidence that the analysis of corticosterone from feathers is a useful tool to evaluate carry-over effects in birds far away from breeding sites, opening new possibilities for future studies in this field.
KeywordsCorticosterone Stress response Pelagic seabird Life-history trade-offs Carry-over effects Cory's shearwater
We are grateful to Oliver P. Love and three anonymous referees for their constructive comments that clearly improved this manuscript. We thank the Serviço do Parque Natural da Madeira, and particularly Paulo Oliveira, Dília Menezes and Carolina Santos, for providing permission to carry out the work on Selvagens and, together with the wardens at the Nature Reserve where this study took place, giving important logistical support. Rui Oliveira made his laboratory facilities available to us and provided invaluable advice. We are grateful to all of those who assisted fieldwork on Selvagens over the years, particularly Hany Alonso and Teresa Catry, and to Ana Sofia Felix and Tiago Carneiro for assistance in the lab. C.P. was supported by a grant under the Subprograma de movilidad postdoctoral en centros extranjeros del Programa Nacional de Movilidad de Recursos Humanos de Investigación funded by the Spanish Ministerio de Educación (EDU 2728/2011, EX2010-0748). Further support was provided by Fundação para a Ciência e a Tecnologia (FCT-Portugal) and the European Regional Development Fund through the strategic project UID/MAR/04292/2013 granted to MARE and PTDC/MAR/121071/2010.
Author contribution statement
CP, JPG, MPD and PC designed the project, CP, JPG, MPD and PC conducted all research and statistical analyses and CP, JPG, MPD and PC wrote the manuscript.
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