Herkunft and Zugverhalten von in der Schweiz ueberwinternden Reiherenten Aythya fuligula: eine Ringfundanalyse.Breeding range and migration pattern of tufted ducks Aythya fuligula wintering in Switzerland: an analysis of ringing recovery data.

摘要

We present the analysis of all recoveries of ringed Tufted Ducks collected at the Swiss Ornithological Institute up to 2004: 4637 recoveries of birds ringed in Switzerland, and 186 recoveries in Switzerland of birds ringed abroad. The large data set allowed for a detailed analysis of the migration pattern of Tufted Ducks wintering in Switzerland. We addressed the following questions: (1) Where are the Tufted Ducks wintering in Switzerland during the rest of the year? (2) Are there differences in migration pat-tern between the sexes and age classes? (3) Do different populations of Tufted Ducks winter in Switzerland? (4) Are there long-term changes in the migration pattern? The Tufted Ducks wintering in Switzerland breed in two distinct areas: central Europe and European Russia/western Siberia. Breeding birds from the eastern European population in between seem to winter preferably in the Baltic Sea area and in Great Britain. Very few birds were recorded in Switzerland as well as in Britain, suggesting that Tufted Ducks consistently winter either in central Europe (area north of the Alps) or in Northern Europe/Britain. Males scatter more during winter than females. Also, on average, males start spring migration in late winter somewhat earlier than females. Between August and October, the ducks return to their wintering grounds. Since the 1970's (i.e., since ringing took place on a regular basis), the date at which 50 % of the recoveries are situated north of 50 [degree]N (which splits Central Europe and the North Sea/Baltic Sea area) is reached about 50 days earlier. Furthermore, this 50 % criterion correlates with the mean temperature in March of lowland Switzerland, suggesting a shift in the wintering grounds depending on the harshness of winter.