(* = Kurzbeitrag)
Einfluss der Wassertemperatur auf das Überwintern der Wasseramsel Cinclus cinclus am Küsnachter Bach (Kanton Zürich).
(von 1994 bis 2006 vergeben)
Winterbestand, Bestandesentwicklung, Bestandesdichte, Wassertemperatur, Nahrungsangebot, Speiballen
Schweiz, Zürich, Küsnachter Bach, Chliweidlibach
Effect of water temperature on wintering White-throated Dippers Cinclus cinclus at the Küsnacht brook near Zurich, Switzerland. The White-throated Dipper population inhabiting the 8.2 km Küsnacht brook has been intensively studied since 1987. In 2002, 16 pairs bred; ever since, population size varied between 11 and 14 breeding pairs. About half way up the brook, a small stream (Chliweidlibach) flows into Küsnacht brook. The small Chliweidli stream is fed by water from a purification plant around 350 m away from the convergence. From December 1990 to February 1992 and in January and February 2009 water temperatures of the Chliweidli stream and the Küsnacht brook were measured. In addition, I collected invertebrate food supply with a 30 × 30 cm Surber sampler, in order to compare it with a sample from 1989. Through the influx of purified water, water temperature in January and February was increased by >4 °C in all study years. Invertebrates available for Dippers were reduced to freshwater hog louse Asellus aquaticus and freshwater shrimp Gammarus sp. The predictability of the safe and easily accessible food led to high Dipper densities along Chliweidli stream (4–5 individuals/350 m) and Küsnacht brook (9–10 individuals/1500 m) in winter 2009. The frequently regurgitated pellets consisted of the strongly chitinized Asellus aquaticus und Gammarus sp. In the year 2011 the purification plant is going to be shut down. The untreated water will then be led to a newly constructed plant at the shores of Lake Zurich. The loss of the stabilizing effect of elevated water temperatures will possibly lead to a local reduction of Dipper densities in winter.
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