A nondescript songbird that skulks in taiga undergrowth, where very difficult to see well. Breeds on Hokkaido, Sakhalin Island, and the Kuril Islands. Very similar to Gray’s Grasshopper-Warbler, which breeds on mainland of far northeastern Asia and has a different song. Migrants very difficult to distinguish from Gray’s, but Sakhalin averages warmer-toned and browner, with perhaps a slightly paler throat. Sings from deep cover, day and night, a hurried, loud, choppy song.