Female Song Rate and Structure Predict Reproductive Success in a Socially Monogamous Bird

Abstract

Bird song is commonly regarded as a male trait that has evolved through sexual selection. However, recent research has prompted a re-evaluation of this view by demonstrating that female song is an ancestral and phylogenetically widespread trait. Species with female song provide opportunities to study selective pressures and mechanisms specific to females within the wider context of social competition. We investigated the relationship between reproductive success and female song performance in the New Zealand bellbird (Anthornis melanura), a passerine resident year round in New Zealand temperate forests. We monitored breeding behavior and song over 3 years on Tiritiri Matangi Island. Female bellbirds contributed significantly more toward parental care than males (solely incubating young and provisioning chicks at more than twice the rate of males). Female song rate in the vicinity of the nest was higher than that of males during incubation and chick-rearing stages but similar during early-nesting and post-breeding stages. Using GLMs, we found that female song rates during both incubation and chick-rearing stages strongly predicted the number of fledged chicks. However, male song rate and male and female chick provisioning rates had no effect on fledging success. Two measures of female song complexity (number of syllable types and the number of transitions between different syllable types) were also good predictors of breeding success (GLM on PC scores). In contrast, song duration, the total number of syllables, and the number of "stutter" syllables per song were not correlated with fledging success. It is unclear why male song rate was not associated with reproductive success and we speculate that extra-pair paternity might play a role. While we have previously demonstrated that female bellbird song is important in intrasexual interactions, we clearly demonstrate here that female song predicts reproductive success. These results, with others, highlight the need for a change in how we view the significance of female secondary sexual traits; traits long underestimated due to a focus on male song.

Female dark‐eyed juncos Junco hyemalis thurberi produce male‐like song in a territorial context during the early breeding season

“…Contrary to this prediction, we observed females singing only in response to a simulated intrusion from a rival female, supporting a function in resource and/or mate defense. Consistent with an adaptive, territorial function, females of multiple temperate species sing most often during aggressive interactions with rival females (Langmore 1998), and recent evidence suggests that female song rate is positively related to fitness in some species (Cain et al 2015, Brunton et al 2016.…”

Evolution of a mating preference for a dual‐utility trait used in intrasexual competition in genetically monogamous populations

“…Intrasexual resource competition offers a mechanism by which a link between an ornamental trait and fecundity could emerge: if ornamented females, for example, are more likely to win competitions with other females for access to resources that enhance fecundity, such as high‐quality territories or food resources, males that prefer ornamented females will have more fecund mates (Tobias, Montgomerie, & Lyon, ). Emerging evidence supports the idea that, as suggested by multiple reviews covering the function and evolution of female ornamentation (Lyon & Montgomerie, ; Tobias et al., ; Webb et al., ; West‐Eberhard, ), female visual and vocal ornaments are often used in female–female competition over resources related to reproductive success (Brunton et al., ; Cain et al., ; Crowhurst, Zanollo, Griggio, Robertson, & Kleindorfer, ; Kraaijeveld et al., ; Krieg & Getty, ; Murphy et al., ,b; Pryke, ; Stankowich & Caro, ; Watson & Simmons, ). For example, female black swans ( Cygnus atratus ) with more curled feathers are more likely to win female–female agonistic interactions, and number of curled feathers also predicts the ability to maintain territory ownership, which leads to higher offspring survivorship (Kraaijeveld et al., ).…”

“…For example, female black swans (Cygnus atratus) with more curled feathers are more likely to win female-female agonistic interactions, and number of curled feathers also predicts the ability to maintain territory ownership, which leads to higher offspring survivorship (Kraaijeveld et al, 2004). In New Zealand bellbirds (Anthornis melanura), females use song to defend breeding territories against other females, and female song rate predicts the number of young fledged (Brunton, Evans, Cope, & Ji, 2008;Brunton et al, 2016). Similar links among female song rate, female territorial defense against other females, and female offspring production occur in house wrens (Troglodytes aedon;Krieg & Getty, 2016) and superb fairy-wrens (Malurus cyaneus; Cain et al, 2015).…”

Analysis of female song provides insight into the evolution of sex differences in a widely studied songbird

“…Similarly, in species in which females have dull plumage, there has been repeated, independent selection on feather color in both males and females (Dale et al, 2015; Hofmann et al, 2008; Price et al, 2014), with females experiencing more evolutionary plumage change than males in some lineages (Price et al, 2014). Even though losses of female song and plumage appear to contribute considerably to dimorphism in signaling traits, the processes and conditions leading to these changes within individual species have not received much attention, particularly in species where female song is rare (Brunton et al, 2016; Kleindorfer et al, 2016a).…”

“…In contrast, relatively few studies have found relationships between female visual signals and fitness proxies, but see: (Amundsen et al, 1997; Bulluck et al, 2017; Cain & Ketterson, 2011; Jawor et al, 2004; Pap et al, 2019). Likewise, many studies have examined the fitness correlates of male song (Catchpole & Slater, 2003; Gil & Gahr, 2002), but only a handful have looked at how female song impacts fitness (Brunton et al, 2016; Cain et al, 2015; Kleindorfer et al, 2016b; Krieg & Getty, 2016a). Although integrated approaches can best untangle the relative contributions of selection on males and females to these signaling modalities (Hebets et al, 2016; Riebel et al, 2019), researchers have seldom included both visual and acoustic phenotypes from both sexes within the same studies.…”