Behaviour 2019
Testing the “Warm-up” Hypothesis for the Evolution of the Dawn Chorus
Juleyska Vazquez-Cardona1, Hester Jiskoot1, Tyler R. Bonnell1, Peter C. Mower1, David M. Logue1, 2. 1University of Lethbridge, Lethbridge, AB, Canada; 2University of Puerto Rico, Mayaguez, , Puerto Rico

Why do many species of birds participate in an early morning dawn chorus? A previous study from our lab showed that male Adelaide’s warblers’ (Setophaga adelaidae) singing performance increases over the course of the morning, suggesting the hypothesis that intense early morning singing is the outcome of an evolutionary arms race to rapidly “warm-up” the vocal apparatus. The present study uses a larger dataset, more precise measures of vocal performance, and a novel analytic approach to characterize changes in vocal performance over time and test whether performance is mediated by air temperature (Ta), as predicted by the warm-up hypothesis. We found that three kinds of vocal performance increase dramatically over the course of the dawn chorus and then hold steady or decrease slightly in the hours after sunrise. We also found that performance was lower at low Ta. This study lends support to the hypothesis that birds are warming-up their voice during the dawn chorus and improves our understanding of the effects of weather on birdsong.