The use of soft songs during territorial intrusion in alarm context in the Ortolan Bunting Emberiza hortulana

Abstract

Animals from many taxa produce low amplitude acoustic signals. In some birds such soft signals were found to be uttered in aggressive context and were the best predictor of subsequent physical attack. This phenomenon is poorly understood and several hypotheses have been proposed to explain the function(s) of the lowered amplitude of such signals. The eavesdropping avoidance hypothesis suggests that the use of low amplitude signals limits the possibility of signal detection by third-party receivers such as predators or conspecific rivals. Herein, we aim to investigate if soft songs in the Ortolan Bunting Emberiza hortulana are used in order to avoid being predated or eavesdropped by potentially threatening conspecifics. We simulated alarm situation by playback of conspecific alarm calls. We measured the overall strength of males’ response to territorial intrusion and number of soft songs in response to a risky situation compared to a control condition. Males showed a weaker approaching response to territorial intrusion and produced more soft songs if previously exposed to conspecific alarm calls and this behaviour is consistent with the eavesdropping avoidance hypothesis. However, we did not observe a complete switch to singing softly in alarm context, and both during the treatment and control males uttered loud calls in response. We suggest that soft songs in the Ortolan Bunting facilitate mediation of the territorial conflict by signalizing change in current motivation. Alternatively, soft songs might be related to readiness to fight or enable addressing signal to a specific receiver within a close range.