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River Warbler (Locustella fluviatilis)

It is quite possible that someone could have breeding River Warblers on their doorstep and not know it. This is a very secretive, skulking species, extremely difficult to see, and the male’s song sounds more like a cricket or cicada than a bird, so it is easily mistaken for something else. The sound is almost mechanical in tone, like the rhythmic “zip-zip-zip” buzzing of a sewing machine, and it is normally performed at night: one study revealed that 90% of all output was in the dark. Moreover, males stop singing as soon as they are paired, so after the brief singing season they vanish into the scrubby hinterland, and many are never detected at all.

River Warblers are birds of Eastern and Central Europe, and found in such habitats as wooded swamps, marshes, bogs and willow scrub, not necessarily near water or rivers. They require very dense but low undergrowth, often including grasses and nettles, and this needs to be interspersed with bushes (often hazel) whose leaf layers are 0.5 m-1.5 m above ground, leaving bare ground underneath where the birds can forage. They thus occupy rather different habitats to Grasshopper and Savi’s Warblers. In common with other Locustella warblers, though, River Warblers walk and creep around under cover, well hidden in their own mini forest. They will also forage along streams and other water-courses.

The nest is typical for a Locustella warbler, a loose cup of dead leaves and grasses about 10 cm in diameter. It is well hidden on or near the ground in dense vegetation, and can usually only be approached along some “tunnel” in the vegetation, like some secret spy hideaway.