Integrated population monitoring of kestrel and western barn owl

    The long-term project aims at identifying the critical phases in the annual cycle of kestrel and western barn owl.

    Aims

    Our aim is to identify the critical phases in the life cycle of kestrel and barn owl. The project shall help to get deeper insights into the population dynamics of these two species and to understand the impact of survival, fecundity, immigration and emigration on population changes. By individually marking kestrel and barn owl nestlings, we hope to improve our understanding of their settlement decisions. We also aim to understand why the two species often show contrasting population trends despite having a lot in common in terms of habitat, prey and nest site.

    Approach

    Using a standardised protocol, we encourage our honorary collaborators to sample data on population size, to mark and resight individuals and to record reproductive success of barn owls and kestrels. We have established several locally collaborating groups to ensure a representative sampling across Switzerland.

    Results

    Several interesting results were obtained from one barn owl population which is intensively studied: barn owl survival is reduced when winters are cold and snowy, because the access to food (voles) is reduced. There is also evidence that life history strategies of individuals differ according to their coloration.

    Components of reproductive success such as clutch size, egg laying date or brood size measured in different populations of kestrels throughout Switzerland varied strongly among years. The components varied also spatially, resulting in part from differences in altitude among study areas but hardly from the amount of arable land. An early egg laying date had a positive effect on clutch size, brood size and body mass of nestlings. As the egg laying date depends on food availability in spring, any conservation action that positively affects food availability in spring could be beneficial for kestrel populations.

    Project management

    Michael Schaub, Martin Spiess

    Partners

    Prof Alexandre Roulin, Université de Lausanne
    Dr Res Altwegg, Avian Demography Unit, University of Cape Town

    Publications

    Zellweger-Fischer, J., M. Schaub, C. Müller, M. Rudin †, M. Spiess & L. Jenni (2011):
    Der Bruterfolg des Turmfalken Falco tinnunculus: Resultate und Erkenntnisse aus fünf Jahren integriertem Populationsmonitoring.
    Roulin, A., R. Altwegg, H. Jensen, I. Steinsland & M. Schaub (2010):
    Sex-dependent selection on an autosomal melanic female ornament promotes the evolution of sex ratio bias.
    Altwegg,R., A. Roulin, M. Kestenholz, L. Jenni (2006):
    Demographic effects of extreme winter weather in the barn owl.
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    The Institute’s commitments

    Kestrel and the Western Barn Owl