Singing on the wing reveals respiratory performance constraints of song production

Abstract

Birdsong is a critical behaviour for reproductive success and therefore exhibits features that reach physiological performance limits. Only few examples of production constraints have been studied in detail. To address this gap in our knowledge, we ask whether singing during flight reaches respiratory and energetic limitations. Male common whitethroats, Curruca communis (formerly Sylvia communis), display three singing modes, perched stereotyped song, variable song during flight and variable song after landing. We compared temporal and frequency modulation characteristics of song for these three modes. When flying, males reduced the duration of syllables and increased silent periods between syllables, which resulted in markedly reduced sound density. These changes in temporal structure and similar minimal pause duration for all singing modes imply that ventilatory changes induced by flight drive these changes in song rhythm, while neither respiratory nor syringeal dynamics indicate limitations in oxygen delivery to vocal muscles. These findings identify song features that are potential indicators of the fitness of the singing bird.