Is the dawn chorus an adaptation to warm-up the voice in Adelaide's warbler (Setophaga adelaidae)?

Abstract

Birds sing intensely during the early morning. I test predictions of the hypothesis that this phenomenon, known as the dawn chorus (DC), is an adaptation to warm-up the voice in male Adelaide’s warblers (Setophaga adelaidae). I also analyze the effects of weather and date on the dawn chorus start time (DCST). I used songs from 29 males recorded in three different years and weather data from a MesoWest weather station. Song performance improves rapidly during the DC, but changes little after dawn. High song-rates lead to rapid improvements in vocal performance. Two out of three measures of performance peak at intermediate air temperatures (Ta). Ta, however, does not exert a strong effect on DCST. Males start to sing later with higher relative humidity, and earlier with increasing precipitation the previous day. This study lends support to the warm-up hypothesis and improves our understanding on the effects of weather on birdsong.