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Titre :	Ammersee area 1966-1996: Trends in selected visiting birds
Auteurs :	Johannes Strehlow, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (37(1) Jan., 1998)
Article en page(s) :	19-45
Résumé :	For part I comprising breeding birds, see Orn. Anz. 36, 1997: 125-142. - Unless stated otherwise, the maxima in the diagrams are the highest daily counts of a year or winter. 32 visiting birds in the Ammersee area are selected which show a trend in numbers since 1966, partly also in the frequency of their occurrence. Of these, essentially more species show an increase in numbers than a decrease (15:3 species), whereas 14 more species exhibit changing trends (table). Above all, the frequent species Tufted Duck (Aythya fuligula) and Coot (Fulica atra) have decreased (Figs. 3, 4). Probably the reason therefore is the transition of lake Ammersee from the eutrophic to the mesotrophic state. This is documented also by a decrease of all waterfowl (Fig. 1). In addition, after an increase for about 10 years also numbers of Mute Swan (Cygnus olor, Fig. 26), Teal (Anas crecca), and Mallard (Anas platyrhynchos, Figs. 28, 29) diminished strongly in the last 15 to 20 years. The fish-eating species Great Crested Grebe (Podiceps cristatus), Cormorant (Phalacrocorax carbo), and Goosander (Mergus merganser) run through a marked maximum at the end of the eighties/beginning of the nineties (Figs. 24, 34), which points to a similar development of available fish amounts. Taking into account all waterfowl, the ecological system Ammersee proves very complex. Thus, at present it is not possible to give simple relations applying to all species. - The increase of 15 species (table) is not specific for the Ammersee area in most cases, but a result of common trends in Middle Europe. Roosts were detected for Hen Harrier (Circus cyaneus) and Merlin (Falco columbarius) with a maximum of 31 and 5 individuals, respectively.

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