Abstract
Sex ratio is an indicator of population health as unexpected biases may indicate potential threats. We studied nestling sex ratio in Black Stork Ciconia nigra populations in order to check potential biases and differences along east–west and north–south gradient across its distribution range in Europe. We also studied variation between years, and checked potential correlations with weather variables. The overall sex ratio of nestlings in Europe was nearly equal with a non-significant deficiency (47.1 %) of males, the larger sex. Although yearly fluctuations in sex ratio were detected, no significant effect of the year alone was found, only simultaneously with population and brood size. There was a tendency to have a higher proportion of female nestlings in larger broods, but the pattern was probably scattered by the effect of reduction of largest broods. Compared to Western and Eastern Europe, a significant deficiency of male nestlings was found in Central Europe (Poland), whereas no differences were found along the north–south gradient. We did not find any effect of temperature, but rainfall during the incubation period was negatively correlated with the proportion of male nestlings in Central (Poland) and Western Europe (France) whereas in North-Eastern Europe (Latvia) the same effect of the precipitation in pre-breeding period was found.
Zusammenfassung
Räumliche und zeitliche Variation im Geschlechterverhältnis von Nestlingen der europäischen Populationen des Schwarzstorches Ciconia nigra
Das Geschlechterverhältnis gibt Aufschluss über die Gesundheit einer Population, da unerwartete Schwankungen auf mögliche Gefahren hindeuten können. Wir untersuchten das Geschlechterverhältnis von Nestlingen in Schwarzstorch Ciconia nigra Populationen, um mögliche Ungleichverteilungen und Unterschiede im Ost-West oder Nord-Süd-Gradienten über seinem gesamten Verbreitungsgebiet in Europa zu entdecken. Wir betrachteten ebenfalls die Variation zwischen den Jahren und untersuchten mögliche Korrelationen mit Wetterbedingungen. Insgesamt war das Geschlechterverhältnis in Europa fast ausgeglichen, mit nicht signifikant geringerem Anteil von Männchen (47,1 %), dem größeren Geschlecht. Obwohl es jährliche Schwankungen gab, war der Jahreseffekt alleine nicht signifikant, sondern nur gemeinsam mit Population und Brutgröße. Tendenziell waren in größeren Bruten auch mehr Weibchen, doch der Zusammenhang war vermutlich verwischt durch Brutreduktion in den größten Bruten. Im Vergleich zu West- und Ost-Europa fiel ein signifikant geringerer Anteil männlicher Nestlinge in Zentraleuropa (Polen) auf. Auf dem Nord-Süd-Gradienten wurde keine Ungleichverteilung festgestellt. Temperatur hatte keinen Effekt, aber Niederschlag während der Inkubation korrelierte negativ mit dem Anteil männlicher Nestlinge in Zentraleuropa (Polen) und Westeuropa (Frankreich). In Nordosteuropa (Lettland) hatte Niederschlag vor der Brutperiode denselben Effekt auf das Geschlechterverhältnis.
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Acknowledgments
We would like to thank all the numerous people who have assisted in the field work and whose years-long work has made this study possible. We also thank two anonymous reviewers and Mirjam Nikolai for the comments on the manuscript. Financial support was provided by European Commission Marie Curie Actions programme (European Re-integration Grant no. 256061 to Ü.V.) and the Polish Ministry of Science and Higher Education (grant no. N304045136 to P.Z.). For making possible to use weather data, we acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu).
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Communicated by O. Krüger.
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Konovalov, A., Kaldma, K., Bokotey, A. et al. Spatio-temporal variation in nestling sex ratio among the Black Stork Ciconia nigra populations across Europe. J Ornithol 156, 381–387 (2015). https://doi.org/10.1007/s10336-014-1135-8
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DOI: https://doi.org/10.1007/s10336-014-1135-8