MARSH WARBLER (Acrocephalus palustris)

Rousserolle verderolle

Acrocephalus_palustris_Marek_Szczepanek.jpgI love this crazy bird ! It is a migrant species nesting in Switzerland and present from May until September. It is found in a large arc to the north of the country along the line of the River Aar and the rivers that drain north from the alps eventually into the Rhine, but throughout this arc occurs only spasmodically, the main range in Europe is to the east of us.

The song is a wild frantic chorus of extremely complex notes and phrases and the literature tells us that it is made up of a large amount of mimicry of other species. However since any individual probably spends more time in its African wintering grounds than in Europe breeding, not many of the model species that it mimics are recognisable to us. It apparently has the largest repertoire of any of the Acrocephalus warblers in Europe. I recorded this bird alongside the Saane River which you can hear in the background:

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But as you can hear the song is delivered with an effort and a wild urgency that few other species can deliver. It sounds completely random but there are features within the song that seem to recur, for example these rapid repetitions that sound as though the bird is tripping over itself seem to occur regularly:

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I am also reliably informed that the slurred rather nasal "tschay" notes in the middle of this sequence are also diagnostic:

The alarm call that I have recorded starts with a rather short "chack" note and then progresses into a churring scolding noise, but whilst this bird did this when I approached too close it then moved into full song, presumably to drive me away ! :

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But it is the ability to imitate other species that is remarkable in this bird. A study from Belgium of 30 different individuals showed that 80% of the song phrases were definitely imitated (the remaining 20% were unknown), and that 80% consisted of an average of 76 different song types in each bird: 45 derived from the wintering grounds in Africa and 31 from other European species. It would seem that young birds begin to learn their song whilst in Europe, but then continue to do so for a further 6-7 months as they migrate across the equator and take up their winter quarters in eastern Africa, picking up song phrases from other species as they go. Once the learning phase is finished the songs learned then become fixed (Dowsett-LeMaire 1979).

So think about that amazing learning and copying process and have another listen to this crazy bird: here is another sequence that you can try and memorise !!

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