The Aquatic Warbler (Acrocephalus paludicola) is an approximately 12 cm tall, nondescript-looking songbird. Its biology instead is spectacular. Its habitat can exclusively be found in wet, low growing sedges marshes in Central and Eastern Europe.
Aquatic Warblers have a strict polygamous mating system. A male mates with several females and females mate with multiple males. Every year they spend the winter in a 6000-7000 km remote African wintering area.
Specialization in an unusual habitat has become a problem for the Aquatic Warbler in the past 100 years. At around the turn of the century it was called the "sparrow of the fens" because of his commoness. However in Central Europe the river fens where it used to breed are now largely destroyed. Especially the intensive drainage, but also the abandonment of traditional forms of use lead to a population decline off about 95% in 100 years. The world population of the Aquatic Warbler today consists of no more than 33000-48000 individuals. The species only breeds in about 50 areas in seven countries. The whole breeding area is as small as the island of Rügen. The Aquatic Warbler is the only globally endangered songbird on the mainland Europe.
In 2003, an agreement on measures to protect the aquatic warbler as a side agreement to the Bonn Convention on migratory species was signed by 12 countries - the first and only international agreement for a "little brown bird". The states have committed to implementing measures to conserve the species.
In Germany there is one last remaining sanctuary for the Aquatic Warbler, the "Lower Oder Valley" National Park, not far away from our project area. There, but also in Poland, Belarus, Latvia and Ukraine, great efforts are being made to preserve the habitat of the Aquatic Warbler.