Geographic song variation and dawn singing behavior of the cerulean warbler (Setophaga cerulea)

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.