Male song of the Aquatic Warbler, a promiscuous bird without paternal care, is more complex than previously thought

Abstract

The Aquatic Warbler Acrocephalus paludicola is one of the rarest European passerines and is characterised by promiscuity, lack of pair-bonds and female-only parental care. This makes the species an important model for studying the function of avian courtship song. The song of the Aquatic Warbler consists of whistle and rattle phrases produced as discontinuous A-, B- and C-songs, which are built by a single rattle, a rattle and a whistle, and more than two phrases of both kinds, respectively. The A- and B-songs are thought to be aggressive signals in male-male interactions, while C-songs are thought to be important for female choice. Here, we analysed recordings of 40 individually marked males, and determined the phrase repertoire. The enumerated repertoire (males recorded for ≥ 10 min) ranged from 16 to 158 (mean 99), however, it did not capture the complete phrase repertoires. We then used models from species diversity ecology to estimate the actual phrase repertoire size, which ranged between 18 and 300 phrases (mean 155). The estimated repertoire was predicted by the number of C-songs. The rattle repertoire was larger than the whistle repertoire, and both positively correlated with the number of C-songs. Our study indicates that male Aquatic Warblers have highly complex phrase repertoires that vary widely in size. Their courtship song is flexible and efficient, enabling relative song complexity to be demonstrated in a short sample, thus facilitating both female attraction through the quick presentation of large phrase repertoires and rival deterrence through the production of many short and simple A- and B-songs.

Agonistic song rate positively correlates with male breeding success and avian malaria infection in a promiscuous songbird with female-only parental care

“…the great reed wrbler), and males with a larger repertoire produce more and tter offspring (Hasselquist et al 1996). The large repertoire size of the aquatic warbler (Osiejuk and Kubacka 2023) justi es an expectation that it should correlate with tness-related parameters (Robinson and Creanza 2019). However, we failed to nd this relationship, which does not support the hypothesis that the evolution of song complexity could be driven by female choice and remain under sexual selection in this species.…”

“…The song sampling and sound analysis are described elsewhere (Osiejuk and Kubacka 2023). Brie y, songs of individually marked aquatic warbler males were recorded between 16:15 and 21:20 hrs from 28 May to 29 July in 2018, using a Marantz PMD 661 digital recorder and a Telinga Pro 7 microphone mounted in a Telinga Universal parabola, as 48 kHz / 16-bit PCM WAV les.…”

“…We obtained (mean ±sd) 703 ±278.1 seconds of recording per male, with 235 ±113.7 phrases per individual. Because aquatic warbler males can present their repertoire e ciently in a few C-songs (Osiejuk and Kubacka 2023), and we used the estimated repertoire size rather than the enumerated one, we think that the recording times that we obtained su ce as a biologically relevant estimate of the repertoire size. Collecting longer recordings while maintaining a fair sample of individuals is challenging in the aquatic warbler, given remote and physically demanding breeding habitat and a narrow time window of peak singing intensity (Dyrcz and Zdunek 1993).…”

Agonistic song rate positively correlates with male breeding success and avian malaria infection in a promiscuous songbird with female-only parental care

“…The song sampling and sound analysis are described elsewhere (Osiejuk and Kubacka 2023) (Dyrcz and Zdunek 1993). The songs of each individual were manually segmented into phrases (Catchpole andLeisler 1989, 1996) in Raven Pro 1.6 (K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology 2022).…”

“…Levels of multi-paternity are high and the breeding success of males is highly asymmetric (Schulze-Hagen et al 1993Dyrcz et al 2002). Males are characterised by high betweenindividual syllable diversity and large repertoires, with the average number of unique phrases in a male estimated at 155 (range 18-300) (Osiejuk and Kubacka 2023). The latter predicts a stronger correlation of song elaboration with reproductive success compared to songbird species with smaller repertoires (Robinson and Creanza 2019).…”