Bestandsudvikling hos Hvidbrystet Præstekrave i Danmark og nabolandene

Ole Thorup, Thomas Bregnballe

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    Abstract

    Changes in distribution and abundance of breeding Kentish Plovers Charadrius alexandrinus in Denmark and neighbouring countries
    This paper describes the changes in the distribution and numbers of breeding Kentish Plover in Denmark and adjacent areas in SW Norway, Sweden, Germany and the Dutch Wadden Sea. We used published and unpublished records and numbers of breeding Kentish Plovers to estimate historical and present occurrence of the species.
    Extensive breeding surveys of Kentish Plovers in 1967-69 and 1971-75 (Dybbro 1970, 1976 and unpubl.) made it possible for the first time to generate reliable estimates of Danish breeding numbers; in 1967-69 136 pairs were found with 70 in the Danish Wadden Sea, and in 1971-75 119 pairs in Denmark and 70 pairs in the Wadden Sea. A nation-wide survey in 1987-89 (Falk & Brøgger-Jensen 1990) and a Wadden Sea breeding survey in 1991 (Fleet et al. 1994) achieved only partial coverage of the potential numbers of Kentish Plover present. Surveys next achieved good coverage of the Danish Wadden Sea and in Denmark in 1996, when Kentish Plovers no longer bred in the country outside the Wadden Sea. During 1996-2020, the species was counted at all its breeding sites in the Danish Wadden Sea annually (Appendix 1); numbers varied between 57 and 106 pairs in 1996-2000, and between 70 and 96 pairs in 2016-20.
    In northern Europe, Kentish Plovers are strictly coastal, found breeding on wide sandy beaches and sandbars and on adjacent grassland in early the stages of succession or which are intensively grazed. As was the case all over NW Europe, the species’ distribution became particularly more restricted during the second half of the 20th century (Fig. 1) at the same time as a drop in the total numbers of pairs in Denmark and all the neighbouring countries (Fig. 3 and 4). However, the reduction in total numbers in Denmark from the first estimate in 1970 until 2020 was much more modest (< 20%) primarily due to the fact that numbers in the key breeding area in Denmark, the Danish Wadden Sea, were stable or perhaps even increased slightly in that period (Fig. 2). In Niedersachsen and the Dutch Wadden Sea numbers declined more than 90% in the same period, whereas numbers in the Schleswig-Holstein Wadden Sea halved between 1970 and 2020 (Fig. 4).
    Elsewhere on the Wadden Sea beaches, Kentish Plovers disappeared or declined to very low numbers during a period of stable numbers on the Danish islands of Rømø and Fanø. Extensive land formation with sparse pioneer vegetation on the beaches and flexible fencing around nest sites that reduced disturbance from beach visitors may have been the primary causes behind the successful maintenance of numbers on Rømø and Fanø.
    In Schleswig-Holstein, targeted management has retained large numbers of breeding Kentish Plovers in three wetlands and coastal meadows embanked in the late 1970s and 1980s. In Margrethe Kog-Saltvandssøen in the Danish Wadden Sea (an area which was embanked in the late 1970s), breeding Kentish Plovers also settled in the years immediately after the embankment. However, in contrast to the three German sites mentioned above, lack of targeted management for species like Kentish Plovers allowed the pioneer vegetation to turn into grassland in this area, so failing to retain nesting birds. As a means of securing good breeding opportunities for Kentish Plovers away from large numbers of beach visitors, we recommend restoring former breeding habitats for the species in Margrethe Kog.
    Due to frequent serial polygamy in the species, absence of pure non-breeders, and a very long breeding period, one count method performs much better than the others. This involves two counts of all birds present in the breeding area, where all individuals are sexed, preferably undertaken in the Danish Wadden Sea between 21 May and 16 June; both counts should be within a fairly restricted time window in order to avoid double-counting the same pair. The number of the most numerous sex at the maximum count is then used as the number of breeding pairs.
    There was high inter-observer variability in the numbers of birds detected on the huge potential breeding areas on the beaches of Rømø (Bregnballe & Thorup 2021). Such breeding sites are difficult to cover properly due to the inconspicuousness of breeding Kentish Plovers, and we recommend the use of very experienced observers with particular skills in this type of breeding habitat.
    Original languageDanish
    JournalDansk Ornitologisk Forenings Tidsskrift
    Volume115
    Issue4
    Pages (from-to)285-300
    Number of pages16
    ISSN0011-6394
    Publication statusPublished - Dec 2021

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