Population dynamics of little owl

    Understanding the dynamics of little owl populations is important for the conservation of this once widespread species.

    Aims

    We study the possible reasons for population changes of four little owl populations in Central Europe. The results may help to develop conservation strategies and to assist in the possible re-colonisation of Northern Switzerland. We study which of the demographic rates are responsible for variation in population growth and whether the mechanisms causing variation are the same in all populations.

    Approach

    Demographic data (capture-recapture data, reproductive success) from four populations (one in Switzerland, three in southern Germany) have been collected by different persons during the last 30 years. We analyse these data with the help of modern statistical methods.

    Results

    Our analyses show that annual variation in survival was the most important factor affecting the little owl populations. By contrast, the highly variable fecundity contributed little to variation in population growth rate. This small impact of reproductive success on population growth can be explained by substantial natal dispersal. None of the studied populations was self-sustainable, but depended strongly on immigrants, which mostly were young individuals from other populations. These effects were stronger, the smaller the spatial extent of the studied populations was.

    Successful conservation of little owls is therefore only possible, if the focus is directed towards a system of local populations. Once a local population has become too small and isolated, the chances to prevent its extinction are low, even if the habitat is optimally managed.

    Project management

    Michael Schaub

    Partners

    Swiss Association for the Protection of Birds SVS/BirdLife Switzerland