Nicolas Strebel, Nicolas Martinez
Hängt die Häufigkeit der Singdrossel Turdus philomelos zur Brutzeit mit der Häufigkeit grosser Gehäuseschnecken zusammen?
(von 1994 bis 2006 vergeben)
Brutbestandsindex, Bestandsentwicklung, Reviere, Dichte, Höhenverbreitung, Nahrung, Nahrungsangebot, Schnecken
Turdus viscivorus, Turdus philomelos, Turdus merula, Turdus pilaris, Turdus torquatus
Misteldrossel, Singdrossel, Amsel, Wacholderdrossel, Ringdrossel
Is the breeding population density of the Song Thrush Turdus philomelos correlated with the abundance of large snails? The population size of the Song Thrush has increased considerably in Switzerland since the mid-2000s. At the same time, an increase in the abundance of landsnails was found in the Swiss Biodiversity Monitoring project. In view of the great importance of snails as food for the Song Thrush, a connection between these developments seems probable. We investigated whether the population sizes of Song Thrushes and snails also correlate at the local scale. We studied 420 sites, distributed over the whole of Switzerland, for which data on breeding bird and landsnail abundance were collected in the Common Breeding Bird Monitoring and the Swiss Biodiversity Monitoring programs. After correcting for a set of habitat covariates, we found a slight correlation between the number of territories of the Song Thrush per site and the abundance of large snails in a sample area located at the border of the corresponding bird census site. We also found a positive correlation between the temporal changes in Song Thrush abundance and the simultaneous changes in the number of large snails on the corresponding site. The increase in the number of snails throughout Switzerland might therefore have contributed to the nationwide increase in Song Thrush populations; however, quantifying the strength of this relationship is difficult based on the available data, and other factors might have contributed to the increase in the population of the Song Thrush, such as the increase in forest area and a climate-induced increase in various other prey animals, especially at higher altitudes.
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