Hushed disputes between noisy neighbours: ovenbirds vary song amplitude during conflicts with territorial rivals

Vocal amplitude represents an important source of variation in animal acoustic signals, yet amplitude is not well studied for most species, especially in field settings where amplitude is challenging to quantify. Previous studies have shown that vocal amplitude is a flexible trait that songbirds can control. In this study, we explored variation in the amplitude of the primary songs of male ovenbirds, Seiurus aurocapilla , to address the question: do ovenbirds modulate their song amplitude in different social contexts? We present the context-dependent amplitude hypothesis: that animals adjust their vocal amplitude across social contexts to maximize communication with intended receivers while minimizing detection by nonintended receivers. We used a high-precision, field-portable sound level meter to measure the amplitude of 213 songs sung by 30 male ovenbirds on their breeding territories. We categorized the contexts in which these songs were sung as either distant countersinging (i.e. directed back-and-forth interactions with a rival male >20 m away in a separate territory), close countersinging (i.e. directed back-and-forth interactions with a rival male <10 m away) and broadcast singing (i.e. singing without back-and-forth interactions with other males). Our recordings demonstrate that ovenbirds sing high-amplitude songs, with a median average amplitude of 76.0 dB(A) (interquartile range: 73.2–77.9, N = 213) across the entire song and a median maximum amplitude of 98.8 dB(A) (interquartile range: 96.0–101.0, N = 213). Our field data reveal that ovenbirds exhibit differences in the amplitude of their songs between the close countersinging context and the broadcast singing and distant countersinging contexts. Songs had higher amplitudes during the broadcast singing and distant countersinging contexts and the lowest amplitudes during the close countersinging context. We conclude that ovenbirds change their vocal amplitude between social contexts and that vocal amplitude is important to ovenbird communication. • Animals may adjust vocal amplitude across different social contexts. • We used a sound level meter to measure the vocal amplitude of wild ovenbird songs. • Male ovenbirds sang high-amplitude songs reaching a maximum of 98.8 dB(A). • Song amplitude varied across contexts with high levels during long-distance singing. • Lower-amplitude songs were used during close-range countersinging interactions.