Discrimination of vocal performance by male swamp sparrows
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In aggressive communication, the interests of signalers and receivers are directly opposed, presenting a challenge to the maintenance of reliable signaling. Index signals, whose production is constrained by physical ability, offer one solution to the reliable signaling problem. Vocal performance, the ability to produce physically challenging songs, is likely such a signal in swamp sparrows. Maximum vocal performance varies between males and is correlated with aspects of quality. However, vocal performance can be modulated in aggressive contexts by increasing the frequency bandwidth and trill rate of songs. This study examines receiver response to (1) differences in performance of the same song types by different signalers and (2) individual modulation of performance between contexts. Results demonstrate that male receivers show differential response to between-male differences in song type performance, but do not show differential response to the smaller scale modulations of performance produced by individuals singing the same song type at different times. This pattern suggests that vocal performance cannot be effectively cheated and may therefore serve as a good example of an index signal.
KeywordsBirdsong Vocal performance Aggression Reliable signaling Communication
The authors would like to thank Barbara Ballentine for providing stimuli for the inter-male discrimination experiment, Susan Peters for her gracious and invaluable help in creating artificial stimuli for the intra-male discrimination experiment, and Kennon Todd for assistance in the field during pilot work for this study. We would like to thank two anonymous reviewers for helpful suggestions in revising the manuscript. We would also like to thank the Pymatuning Laboratory of Ecology for logistical support and the Pennsylvania Game Commission for access to study sites. This work was funded by the University of Miami College of Arts and Sciences and the University of Pittsburgh’s Arthur and Barbara Pape Endowment.
The experimental methods for this study complied with current rules and regulations within the USA.
Conflicts of interest
The authors declare that they have no conflict of interest.
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