Understanding the population dynamics of white storks

    Successful conservation of the white stork is contingent upon an improved understanding of the factors affecting population trends.

    Aims

    The white stork went extinct in Switzerland in 1950. Due to the reintroduction project by Max Bloesch and Storch Schweiz the population has increased again to more than 200 breeding pairs. Will this increase continue, or will the population start to decline again?

    The project aims at understanding which environmental factors affect the population dynamics of white storks. This may help to derive conservation actions suited to maintain the positive trend of white stork populations in Switzerland.

    Approach

    The white stork population has been accurately surveyed for more than 100 years. The nestlings are, with few exceptions, systematically marked with rings. Ring resightings and ring recoveries from Switzerland and abroad give valuable information on behaviour, life histories, mortality causes, age structure, migratory flyways as well as on stopover and wintering sites. These data are being analysed with modern statistical methods. Similar data are available from other countries, which allows for interesting comparisons.

    Significance

    The history of the white stork in Switzerland in the 20th century was characterized by ups and downs. To prevent that the species goes extinct for a second time in Switzerland, all the available data needs to be analysed to derive useful conclusions for conservation steps.

    Results

    Is the future of the white stork bright? Statistical analyses give a clear answer: the Swiss population is nowadays self-sustaining and increases at a rate of 3 % annually. The high survival rate of adults (annual survival: 86 %) plays a key role for this positive development. However, because the populations are very sensitive to small changes in adult survival, it is crucial to mitigate potential dangers for storks. The most important factors threatening adults are electrocution and poaching in Africa. Newly created wet meadows at several places in Switzerland shall help to increase reproductive output, which still is low (1.65 fledglings/pair) compared to that from other populations.

    Project management

    Michael Schaub

    Partners

    Storch Schweiz
    Prof Jean-Dominique Lebreton, Centre d'Ecologie Fonctionelle et Evolutive CEFE, Montpellier