Blue-headed Vireo was singing in our yard this morning, its song not always easy to tell from Red-eyed Vireo's. The pauses in between its song phrases compared to Red-eyed's is so long make me think I could fall asleep during the pauses, ZZZZZ (that is one way I remember it). The quality of the song phrases are different between the two species as well. Learn bird songs, you will hear many more than you ever see.
Blue-headed
Red-eyed
(photo from another time)