Abstract:
This study presents the results of research into the vocal behavior of the Cerulean
Warbler, a small, migratory songbird with learned songs that breeds in the eastern U.S. and
southern Canada and winters in northern South America. Specifically, I 1) assessed patterns of
geographic variation in the species’ songs, as well as 2) characterized the unique period of
singing that occurs prior to sunrise, known as “dawn song.” I found that Cerulean Warbler song
structure within the species’ core breeding range, where I had high power to discriminate
differences, was highly uniform in all of the acoustic variables measured. Songs were
remarkably constrained in their acoustic features: all songs were composed of 2-4 sections and
had similar durations and frequency bandwidths. I failed to find geographically structured
singing, or “dialects.” The dawn singing behavior of paired male Cerulean Warblers was best
explained by seasonality (Julian date), although the breeding stage of the pair’s nest, as well as
weather (rain, wind, and temperature) also influenced certain aspects of dawn song. Early in the
breeding season, males sang at high rates, for long durations, and their dawn song bouts ended
after sunrise. By mid-season, many males stopped singing dawn song, but those that continued
sung at slower rates, for shorter durations, and their dawn bouts ended well before sunrise.
