The red-eyed, blue-headed and yellow-throated vireos have similar songs. Their songs can be differentiated by the tonal quality and the length of the intervals between phrases. The red-eyed vireo delivers his phrases regularly with about a 2-second interval. The blue-headed vireo has the purest sound, the slowest song and the intervals between phrases is irregular. The yellow-throated vireo has the lowest pitch and is harsher than the other two.
Red-eyed vireo
Phrases every 2 seconds (Pieplow 2017).
Interval between phrases is typically regular.
Blue-headed vireo
More musical (purer tones)
Lower pitch
Slower song than red-eyed vireo: longer interval between phrases. Interval length is typically irregular (Morton and James 2020).
Yellow-throated vireo
Three eight…thirty-eight… (Pielow 2017)
Lower pitched and more buzzy/harsher than red-eyed and blue-headed vireo (James 1984c, Pielow 2017)
Typicaly a second between phrases (Rodewald and James 2020)
References:
Pieplow, Nathan (2017). Peterson Field Guide to Bird Sounds of Eastern North America. Houghton Mifflin Harcourt, Boston, MA.