File:DSC 8858 Rousserolle effarvatte Acrocephalus scirpaceus (50180833053).jpg

In Switzerland, the Red-winged Warbler mainly inhabits the wetlands of the Plateau, with more than 90% of its numbers below 600 m. It is sporadic in the Alpine valleys and the Jura. In recent years, breeding at high altitude has been confirmed at Lac des Rousses F 1060 m (P. Durlet) and Lac de Joux VD 1000 m (Cl. Guex, Cl. Vaucher) and is probable at Geschinen VS 1340 m (R. Lupi) and Lenkerseeli BE 1070 m (K. Rösti).

The Effarvatte nests along calm waters, ditches and reed-lined streams, even in reedbeds as small as 20 m2 if the stems are sufficiently robust and tightly packed; in certain ideal sites, such as the Grande Cariçaie, it can even aggregate more than 70 territories/10 ha.

Numbers and distribution have hardly changed across Switzerland since 1993-1996, despite local variations: on Lake Neuchâtel, populations increased at the end of the 1980s, before experiencing occasional declines since 2010; in the canton of Zurich, the Effarvatte is the only long-distance migrant to show a positive trend between 1988 and 2008; finally, on Lake Constance, it suffered losses between 1980 and 2010, especially in the hinterland, while remaining stable in its main hotspots. In Germany, where there has been a further decline since the beginning of the millennium, as in France, numbers have recovered after a long period of decline, but the trend is negative in Italy and at Lake Neusiedl A. The European population is stable overall.

In a probable response to climate warming, the Effarvatte is arriving here earlier and earlier; it is increasingly anticipating the start of its breeding season without bringing forward the end date, which would enable it to increase the number of breeding attempts and could explain why it is one of the few long-distance migrants to maintain its numbers. Although its densities are particularly high in marshy areas between the second and fourth years after mowing, over-frequent maintenance of marshes and ditches can also lead to localised falls in numbers.

Population
9,000-11,000 pairs (2013-2016)
Groupe Fauvettes et alliés Fauvettes et alliés
Parrainage
Michael Götsch

© Mathias Schäf