BIRDSONG AND SOUND TRANSMISSION: THE BENEFITSOF REVERBERATIONS

Abstract Animal vocalizations used for long-distance communication are shaped by acoustic properties of the environment. Studies of the relationship between signal design and sound transmission typically focus on habitat-induced limitations due to signal attenuation and degradation. However, signal design may not entirely be explained by habitat limitations, but rather by beneficial consequences of reverberations. Narrow-frequency bandwidth notes (NFB notes) are pure notes that change little in frequency, and are typical for many bird species living in dense tropical forests. In contrast to frequency-modulated notes, we show that reverberations lead to a longer and louder signal after transmission for NFB notes. Furthermore, playback experiments to territorial males of an African passerine indicated that longer notes led to a stronger behavioral response. These results suggest that reverberations may benefit signal efficiency depending on the signal design, and add new insight into the selection pressures imposed on acoustic signals by the environment. Canto de Aves y Transmisión de Sonido: Beneficios de las Reverberaciones Resumen. Las vocalizaciones utilizadas por animales para la comunicación a larga distancia están condicionadas por las propiedades acústicas del entorno. Los estudios sobre la relación entre el diseño de las señales y la transmisión del sonido suelen centrarse en los límites impuestos por el hábitat debido a la atenuación y degradación de la señal. Sin embargo, es posible que el diseño de la señal no esté regido exclusivamente por las limitaciones del habitat, sino por las consecuencias beneficiosas de las reverberaciones. Las notas de frecuencia de banda estrecha (notas NFB) son notas puras que cambian poco de frecuencia y son típicas de varias especies que habitan bosques tropicales densos. Al contrario que en las notas de frecuencia modulada, mostramos que las reverberaciones alargan y aumentan la señal de las notas NFB. Asimismo, experimentos de playback con machos territoriales de un paseriforme africano indican que las notas más largas provocan una mayor respuesta. Estos resultados sugieren que las reverberaciones pueden mejorar la eficiencia de la señal, dependiendo del diseño de la misma, y añaden un nuevo componente a nuestro conocimiento sobre las presiones selectivas impuestas por el entorno sobre las señales acústicas.

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