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Journal of Ornithology

, Volume 154, Issue 3, pp 769–774 | Cite as

Seasonal variation in Eurasian Wigeon Anas penelope sex and age ratios from hunter-based surveys

  • Kevin Kuhlmann Clausen
  • Lars Dalby
  • Peter Sunde
  • Thomas Kjær Christensen
  • Bjarke Egelund
  • Anthony David Fox
Original Article

Abstract

Demographic monitoring is vital for tracking and modelling the population dynamics of highly mobile bird populations. However, different types of monitoring can sometimes lead to different outcomes, and understanding the causes of equivocal results is an important step to advance future monitoring schemes. This study found consistent seasonal variation in Eurasian Wigeon Anas penelope sex and age ratios among Danish hunter-based wing surveys, and describes how accounting for this variation might explain reported discrepancies between this and other monitoring methods. Early season flocks were dominated by adult males, and juvenile proportions were highest in November and significantly lower before and after this peak. Nationwide field assessments undertaken in January 2012 showed no significant differences from sex and age ratios in the wing survey data from that particular hunting season (2011/2012), indicating that this survey is a good predictor of Wigeon demography. These results highlight the need to account for consistent temporal variation in such demographic time series when using the results to model population parameters.

Keywords

Wing survey Field counts Reproduction Demography Hunting bag Management 

Zusammenfassung

Jahreszeitliche Schwankungen in Geschlechterverhältnis und Altersstruktur bei der Eurasischen Pfeifente ( Anas penelope ) anhand von Erhebungen durch Jäger

Für die Nachverfolgung und Modellierung populationsdynamischer Prozesse ist bei hochmobilen Vogelpopulationen ein demographisches Monitoring von entscheidender Bedeutung. Unterschiedliche Arten des Monitorings können jedoch gelegentlich zu unterschiedlichen Resultaten führen, und das Verständnis der Ursachen von mehrdeutigen Ergebnissen ist ein wichtiger Schritt in der Entwicklung zukünftiger Monitoring-Systeme. In den Erhebungen dänischer Jäger fanden sich durchgängig jahreszeitliche Schwankungen im Geschlechterverhältnis und in der Altersstruktur der Eurasischen Pfeifente (Anas penelope); diese Studie beschreibt, wie die Berücksichtigung solcher Unterschiede eventuell die Diskrepanzen zwischen den Ergebnissen aus unterschiedlichen Monitoring-Methoden erklären könnte. Schwärme zu Beginn der Saison wurden von adulten Männchen dominiert, während der Anteil junger Vögel im November am höchsten und vor und nach diesem Spitzenwert signifikant niedriger war. Im Januar 2012 landesweit durchgeführte Freiland-Bewertungen zeigten keine signifikanten Unterschiede im Geschlechterund Altersverhältnis zu den Erhebungen dieser speziellen Jagdsaison (2011/2012), was nahelegt, dass eine solche Erhebung ein guter Prädiktor für demographische Aussagen bei Pfeifenten ist. Diese Ergebnisse unterstreichen die Notwendigkeit, konsistente zeitliche Schwankungen in derartigen demographischen Zeitreihen zu berücksichtigen, wenn die Ergebnisse dazu benutzt werden, Populationsmerkmale zu modellieren.

Notes

Acknowledgments

We owe an enormous debt to all the hunters who have voluntarily contributed to the Danish wing survey over many years and to Ib Clausager for initiating and running the scheme for many years. We acknowledge funding from the Forest and Nature Agency (latterly Nature Agency) to support the determination of the sex and age ratios among the wing samples of common quarry species and contributed to the analysis presented here. We would also like to thank the Danish Agency for Science, Technology and Innovation for financial support to L.D.’s PhD project.

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Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2013

Authors and Affiliations

  • Kevin Kuhlmann Clausen
    • 1
  • Lars Dalby
    • 1
    • 2
  • Peter Sunde
    • 1
  • Thomas Kjær Christensen
    • 1
  • Bjarke Egelund
    • 1
  • Anthony David Fox
    • 1
  1. 1.Wildlife Ecology Group, Department of BioscienceAarhus UniversityRøndeDenmark
  2. 2.Ecoinformatics and Biodiversity Group, Department of BioscienceAarhus UniversityAarhus CDenmark

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