Martinez, N. & T. Roth
(* = Kurzbeitrag)
Bestandsentwicklung und Brutbiologie des Gartenrotschwanzes Phoenicurus phoenicurus in der Nordwestschweiz.
(von 1994 bis 2006 vergeben)
Bestandsentwicklung, Bestandstrend, Brutgebiet, Siedlungsdichte, Landwirtschaft, Brutbiologie, Geschlechterverhältnis, Neststandorte, Brutphänologie, Bruterfolg, Nistkasten, Habitatwahl
Basel-Landschaft, Basel-Stadt, Solothurn, Schweiz
Population dynamics and breeding biology of the Common Redstart Phoenicurus phoenicurus in Northwestern Switzerland. The Common Redstart strongly declined in the second half of the last century in Switzerland. The species is thus classified as near threatened and is one of 50 priority species for recovery programs. We collected data on breeding biology between 2009 and 2016, including data on density of territories per habitat, on adult sex ratios, and on clutch sizes and laying dates of 133 nests. We also combined our data with data from other sources. We counted 270 to 280 territories of the Common Redstart in the cantons of Basel-Stadt and Basel-Landschaft and assume that Northwestern Switzerland still holds a population of national importance comprising about 300 – 330 territories. Compared to a census in 1993 / 1995, however, the population clearly declined. According to our habitat model, the decrease of high stem orchards is the main factor explaining the decline in Common Redstarts. The highest densities were found in areas with diverse land use facing southwards. Allotment gardens held a much higher proportion of the current population than in 1993 / 1995. Orchards, allotment gardens and groups of trees are important for the occurrence of the species. The preservation of such habitats, and in particular of existing structurally rich high stem orchards, is crucial. The existing small-scale structural diversity, including patches of bare ground and sparse vegetation, has to be preserved and increased. Our data on breeding biology showed that the adult sex ratio, measured as the proportion of adults that are males, was 0.58, suggesting that females have higher mortality than males. In almost 50 % of clutches, the first egg was laid in April. Compared to previous studies from Central Europe, this suggests an advancement of egg-laying. Common Redstarts seemed to prefer boxes with one large or two small openings, but mortality in boxes with one large opening was relatively high, mainly due to predation. Based on the available data, preferable nest boxes to support Common Redstart populations would have two small openings or one single high, but narrow opening.
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