A small, plain old world warbler of dense undergrowth. Note the narrow dark line through eye and the narrow white line above the eye. Occurs in forest understory, dense shrubland, bamboo thickets, and forest edges. Usually secretive and hard to see well, but males sometimes sing from an exposed perch. Song is a long introductory tone followed by a rapid warble, “uuuuuu-guisu,” from which the Japanese name is derived. Introduced to the Hawaiian Islands where it occurs on all of the main islands.