Abstract
How information transmission processes between individuals are shaped by natural selection is a key question for the understanding of the evolution of acoustic communication systems. Environmental acoustics predict that signal structure will differ depending on general features of the habitat. Social features, like individual spacing and mating behavior, may also be important for the design of communication. Here we present the first experimental study investigating how a tropical rainforest bird, the white-browed warbler Basileuterus leucoblepharus, extracts various information from a received song: species-specific identity, individual identity and location of the sender. Species-specific information is encoded in a resistant acoustic feature and is thus a public signal helping males to reach a wide audience. Conversely, individual identity is supported by song features susceptible to propagation: this private signal is reserved for neighbors. Finally, the receivers can locate the singers by using propagation-induced song modifications. Thus, this communication system is well matched to the acoustic constraints of the rain forest and to the ecological requirements of the species. Our results emphasize that, in a constraining acoustic environment, the efficiency of a sound communication system results from a coding/decoding process particularly well tuned to the acoustic properties of this environment.
Highlights
Acoustic communication systems, such as birdsongs or human language, are likely to be shaped by natural selection [1]
Whitebrowed warbler males are highly tolerant towards song simplification in species-specific recognition and seem to disregard parameters that are substantially altered during transmission: the duration of notes and silences, the fine intra-note frequency modulation and the amplitude modulation
We conclude that the relevant parameter is the average slope of the slow frequency modulation of the carrier frequency, a propagation-resistant parameter, enabling species identity information to be transmitted at long range
Summary
Acoustic communication systems, such as birdsongs or human language, are likely to be shaped by natural selection [1]. Environmental and social constraints represent potential forces influencing how information is encoded in acoustic signals by the sender as well as how perceived sounds are processed by the receiver [2,3,4,5,6] This is a key question for the understanding of communication processes, the identification of these constraints is problematic because, 1) most natural systems fluctuate unpredictably and, 2) presently observed biological phenomena are likely to be the result of a complicated and chaotic evolutionary history [7]. In tropical rain forests, evolutionary constraints upon sound communication due to dense vegetation have likely been stable over the past millennia up to present [8,9] This represents a unique opportunity to link present biological processes with environmental constraints that have remained the same for ages. This paper describes how the information transfer supported by the simple and stereotyped song of a typical bird of the Brazilian Atlantic rainforest, the white-browed warbler, Basileuterus leucoblepharus (Aves: Passeriformes: Fringillidae: Parulini), is well matched to the acoustic propagation constraints of the rainforest and to the ecological requirements of this species
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