On the natural history of duetting in White-browed Coucals: sex- and body-size-dependent differences in a collective vocal display

Abstract

Avian duets have long fascinated biologists, but much remains unknown about what information may be contained in these collective displays and how duet structures vary between taxa. In this study, we describe the structure and performance rules of duets in White-browed Coucals Centropus superciliosus, a tropical non-parasitic Cuckoo. We recorded vocal behaviours of 11 focal pairs and measured temporal, frequency, and amplitude characteristics of their duets. Molecular sexing and radio telemetry revealed that duets were initiated by both sexes, but the majority of them were led by the male. Moreover, we found that duet contributions were sex specific with females producing lower-pitched songs than males, reflecting the general size dimorphism in this species. Finally, we also found that song peak frequencies varied with body size within each sex, suggesting that songs used in duets may act as index signals of body size. We speculate that sexual selection has driven White-browed Coucals to sing as low as possible, a notion that is further supported by our observation of special singing postures that may help in lowering song pitch even further.

A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection

“…This brings us to the hypothesis that the frequency of acoustic signals may be sexually selected, if frequency acts as an indicator of an individual’s size, dominance or fighting ability. In various taxa, the frequency of male vocalisations indeed seems to indicate individual body size and can influence territory establishment (or other forms of male − male competition), attractiveness (female choice, based on the ability to discern male size differences by vocal frequency) and ultimately an individual’s reproductive success (Morris and Yoon, 1989; Apicella et al ., 2007; Charlton et al ., 2007; Hardouin et al ., 2007; Vannoni and McElligott, 2008; Forstmeier et al ., 2009; Brumm and Goymann, 2017; Kirschel et al ., 2020). Thus, if low‐frequency sounds are advantageous in inter‐ and intrasexual interactions (Davies and Halliday, 1978; Wagner, 1989; Briefer et al ., 2010; Bro‐Jørgensen and Beeston, 2015; but see Fischer et al ., 2004), we predict correlated evolution of male vocal frequency and indices of the intensity of sexual selection such as male‐biased sexual size dimorphism (Trivers, 1972; Fairbairn, 1997).…”

Previously unknown behavior in parasitic cuckoo females: male-like vocalization during migratory activity

“…By contrast, the advertising 'cu-coo' call of Common Cuckoo male is especially well studied (Fuisz and De Kort 2007;Jung et al 2014;Wei et al 2015;Kim et al 2017a;Li et al 2017;Moskát et al 2017Moskát et al , 2018Zsebök et al 2017;Benedetti et al 2018;Tryjanowski et al 2018;Deng et al 2019a;Xia et al 2019), including its rare aberrant version 'cu-kee' (Møller et al 2016;Moskát et al 2021). It is well known, however, that female birds can produce song and/or male-like advertising vocalization in several species (Odom et al 2014;Boeme and Goretskaia 2016), including non-parasitic tropical cuckoos (Brumm and Goymann 2017), and duets and chorus are especially characteristic for such species (Tobias et al 2016). Besides, in some species females have been found to sing when the male disappeared or when the testosterone level experimentally enhanced (Garamszegi et al 2007).…”

A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection

“…This brings us to the hypothesis that the frequency of acoustic signals may be sexually selected, acting as an indicator of an individual's size, dominance or fighting ability. In various taxa, the frequency of male vocalizations indeed seems to indicate individual body size and can influence territory establishment (or other forms of male−male competition), attractiveness (female choice) and ultimately an individual's reproductive success (Morton 1977;Fitch & Hauser 2002;Apicella et al 2007;Hardouin et al 2007;Mager et al 2007;Vannoni & McElligott 2008;Forstmeier et al 2009;Brumm & Goymann 2017). For instance, the frequency of advertising vocalizations negatively correlates with body size in males of common toads Bufo bufo and during the mating period smaller males were less often attacked by larger males when natural croaks of the small males were experimentally replaced by deep croaks (Davies & Halliday 1978).…”