ヤチセンニュウ Locustella naevia

Extremely skulky warbler. Plumage dark gray-brown overall with wide black streaks on back; also note long undertail coverts with big dark centers. Favors damp grassy thickets, heaths, and other rank shrubby habitats, often near water. Very skulking, and rarely seen unless singing. Sings from perch in grass or low bush, mainly late in the day (sometimes at night): a prolonged, insectlike, reeling trill. Calls include a high-pitched “pik.”