Gray's Grasshopper Warbler

Gray’s grasshopper warbler is a small migratory Locustellidae with an unstreaked olive-brown back, uniformly grey breast, buff belly and plain dull-orange undertail coverts. It was formerly grouped with the Sakhalin grasshopper warbler, and both were once included in the broad assemblage called Old World warblers. The combination of unmarked upperparts and grey breast helps distinguish it from strongly streaked grasshopper warblers (Wikipedia general species account).

It breeds across southern Siberia, northeastern China and Korea and travels to Southeast Asia for the non-breeding season. Breeding habitat is in lowland and coastal forest or thickets. Unlike the prolonged insect-like reel produced by several European Locustella, its song is a short, loud and more musical phrase. Sulawesi records therefore concern a migrant rather than a resident endemic. The opened account did not give dependable diet, clutch, incubation or body measurements, so these remain unstated (Wikipedia general species account).