Female blue tits sing frequently: a sex comparison of occurrence, context, and structure of song

Abstract

In species with mutual mate choice, we should expect adaptive signaling in both sexes. However, the role of female sexual signals is generally understudied. A case in point is female birdsong that has received considerably less attention than male song. This holds even for well-studied species such as the blue tit (Cyanistes caeruleus), an important model in evolutionary ecology. Although there have been anecdotal reports of female song from three populations, there are no quantitative studies on female song in this species. Here, we report systematic sampling from a population of individually marked blue tits over 3 years, revealing that females sang frequently throughout the sampling period. Notably, daytime singing of females occurred in functionally similar contexts as in males (agonistic, solo song, and alarm contexts) but females had lower song output than males and were not observed singing dawn song, while males showed long singing displays at dawn before copulations take place. Female and male song overlapped substantially in acoustic structure (i.e., same song types or peak frequency) but females had smaller individual song-type repertoires, shorter trills, and lower vocal consistency. Differential selection pressures related to functional differences in male and female song might explain the observed variation in acoustic structure. With the first quantitative study of female song in such a well-studied species, we hope to stimulate further investigations into the functions of female singing, especially in the Northern temperate zones where female song may have been overlooked, not only in this but perhaps in other monomorphic species.

Sex differences in singing behaviour are predicted by territoriality and biparental care in songbirds

“…Recent studies confirm that female song is regularly overlooked and underestimated, even in well-studied temperate breeding birds (e.g.,. barn swallows, Hirundo rustica 68 ; blue tits, Cyanistes caeruleus 69 ). This might in part occur because female song can take place at different times of the day 69 , times of the year 55 , populations 70 or in different contexts 71 from male song.…”

A dawn and dusk chorus will emerge if males sing in the absence of their mate

“…Several studies report differences between song produced during the day and dawn song, in particular in terms of song output [13,20]. The ‘absent mate’ hypothesis predicts such difference in song output, if male song rate increases with the time the female has been absent (as shown in figure 2).…”

“…We test the 'absent mate' hypothesis by examining the validity of the two underlying criteria in a nest-box-breeding population of a common and well-studied passerine bird, the blue tit Cyanistes caeruleus [7,8]. Blue tits exhibit a pronounced dawn chorus and a less pronounced dusk chorus [9][10][11][12][13]. In the early breeding season males on average wake up and start their activity earlier in the morning than females, and females go to roost earlier than males in the evening [14,15], implying that criterion 1 is met in blue tits.…”

Evolution of female song and duetting in the chaffinch (Fringilla) species complex

“…This lability has led researchers to examine the conditions under which it evolves. Despite a recent wave of observations documenting female song for the first time in temperate songbird species (Magoolagan et al 2019, Patchett et al 2021, Langmore 2022, Liu et al 2022, Moyer et al 2022, Sierro et al 2022), female song still appears to be more common in tropical and subtropical species (Slater and Mann 2004, Price 2009, Logue and Hall 2014, Odom et al 2014). Tropical environments typically provide lower levels of seasonality and more consistent resource availability than temperate ones (Slater and Mann 2004, Archibold 2012), and as a result tropical species tend to have longer territory ownership, reduced migration, reduced brood size, and greater rates of social monogamy (Kunkel 1974, Langmore 1998, Hall 2004, Slater and Mann 2004).…”