Reed Buntings are sparrow-sized but slim, with a deeply notched tail. The male has a black head, white collar and a drooping moustache. Females and winter males have a streaked head. In flight, the tail looks black with broad, white edges.
https://files.ohai.social/media_attachments/files/112/011/548/906/973/594/original/d366d5042f12485a.jpg