I’m a Song Sparrow, and song is what I do. This bird could be heard almost every morning not long after sunrise on the north side, right next to the paved perimeter trail. When walkers or runners passed, it sometimes ducked down or behind the bush, and sometimes just ignored them and kept on belting out its tune. Notice that it gets an answer sometimes, and it changes its melody in response.
Song Sparrows are talented singers; read more about them here: