Abstract A mated female was observed singing in a color-banded population of Common Yellowthroats (Geothlypis trichas) in New York State in 2011. This female continued to sing, often concurrently with her mate, for ∼1 week, at which time she completed nest construction and was not observed singing for the remainder of the season. Her song did not resemble any normal Common Yellowthroat song or vocalization. No previous publications have described female song in this species; common explanations for female song in other species include abnormally high testosterone levels, development of male-like characteristics with age, and increased territory defense demands at high densities. We found little support for any of these hypotheses, as our singing female was within the normal range for breeding density, testosterone, morphology, ornamentation, and several physiological parameters. We did not know the age of our female and could not discount old age as a cause of singing; however, other known-age, old female...