Relationships among song characteristics in Japanese tits
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Relationships among song characteristics in Japanese tits Shoji Hamao1 · Ayano Inoue2,3 · Takehiko Kamito2 Received: 10 September 2019 / Accepted: 24 June 2020 © Japan Ethological Society 2020
Abstract Birdsongs often contain two simultaneous, harmonically unrelated sounds; however, little is known of the function of this two-voice phenomenon. We hypothesized that it contributes to increases in song speed and note repertoire, which are important song characteristics in sexual selection. We analyzed six song variables in Japanese tits (Parus minor) and found positive correlations between all possible pairs of the proportion in length of two-voice vocalization, note rate, and note type repertoire, which is consistent with our hypothesis. This finding is a first step towards determining the function of two-voice vocalization in song communication. Keywords Japanese tit · Note rate · Note type repertoire · Parus minor · Two-voice phenomenon
Introduction Songs of male birds have several different characteristics that may be sexually selected. For example, song speed and frequency bandwidth are under sexual selection pressure (Møller et al. 1998; Ballentine et al. 2004; Nishida and Takagi 2018). Because muscles and the nervous system control the syrinx and affect song speed and bandwidth (Podos 1997; Suthers et al. 1999), these song characteristics are related to the physical condition of the males. A recent study in skylarks (Alauda arvensis) showed that the duration of the gap between syllables is long when the inter-syllable frequency shift is large (Geberzahn and Aubin 2014), suggesting that rapid frequency change and greater frequency modulation make singing more difficult. In addition, note or song repertoire size contributes to reproductive success through female choice and male–male interactions (Searcy and Andersson 1986; Catchpole and Slater 1995). Because song learning occurs during the early period of life and therefore involves developmental costs, a large note or song repertoire indicates higher male quality (Nowicki and Searcy * Shoji Hamao [email protected] 1
Department of Zoology, National Museum of Nature and Science, 4‑1‑1 Amakubo, Tsukuba 305‑0005, Japan
2
Department of Natural Science, International Christian University, 3‑10‑2 Osawa, Mitaka 181‑8585, Japan
3
Present Address: Nerima‑ku, Tokyo 176‑0001, Japan
2004; Ritchie et al. 2008). Thus, songs with various characteristics at a high level involve costs for the singers and therefore advertise singer quality as an honest signal (Zahavi 1975; Guilford 1995). The two-voice phenomenon, which is the simultaneous production of two separate, harmonically unrelated sounds (Greenewalt 1968; Miller 1977), is common in songs of several bird species (reviewed in Suthers 1999). When birds control each part of the syrinx, a two-part organ, independently, they produce two different sounds simultaneously (Gaunt et al. 1982; Goller and Larsen 1997). Although the physical mechanism of this vocalization pattern has been studi
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