Grasshopper Warbler

The Grasshopper Warbler is a small, heavily streaked, olive-brown warbler that is far more often heard than seen. Its plumage is finely streaked above and shows subtle streaking on the undertail coverts as well, with plain buffy underparts, and it moves in a low, mouse-like manner through dense vegetation, rarely coming into the open.

Its name refers not to its diet but to its extraordinary song: a continuous, high-pitched, mechanical reeling trill, remarkably insect-like and sustained for long periods, often likened to the sound of a fishing reel or an old-fashioned sewing machine.

Because it is so skulking and its ventriloquial song can be difficult to pinpoint, this is considered one of the more challenging European warblers to actually see well, even when clearly audible nearby.

Key field marks

• Finely streaked olive-brown upperparts
• Streaked undertail coverts, unusual among warblers
• Plain buffy underparts
• Rounded wings and a long, graduated tail
• Skulking, mouse-like movement through low, dense cover

Similar species

• Sedge Warbler: also streaked but shows a bold pale supercilium and an unstreaked rump, and gives a completely different scratchy, varied song rather than a mechanical reel.
• Savi's Warbler: closely related and similarly reeling in song, but plainer and unstreaked above, a rarer and more southerly/easterly species.
• Reed Warbler: plain, unstreaked upperparts, quite different from the heavily streaked Grasshopper Warbler.

Grasshopper Warblers breed across much of Europe and into western Asia, favouring scrubby, tussocky grassland, young conifer plantations with dense ground cover, heathland edges, and wetland margins with thick low vegetation.

They are long-distance migrants, wintering in sub-Saharan Africa, and the species is highly sensitive to changes in vegetation structure, often shifting territories between years as habitat conditions change, for example as plantations mature and lose their dense ground cover.

Males sing from within low cover, sometimes turning their heads while singing, which can make the ventriloquial, reeling song even harder to pinpoint precisely.

Voice

The song is a remarkable, sustained, high-pitched mechanical reeling trill, often continuing unbroken for a minute or more, closely resembling the sound of a fishing reel being cast or an insect's stridulation, which gives the species its common name.

Feeding

Grasshopper Warblers glean insects and spiders from low vegetation and the ground, foraging in a furtive, mouse-like manner that keeps them largely hidden from view.

Nesting and breeding

The nest is a well-hidden cup built low in dense grass or scrub, often close to the ground. Clutches typically contain five to six eggs.