Abstract
BackgroundTerritorial songbirds vocalise intensively before sunrise and then decrease their vocal activity. This creates a communication network that disseminates essential information for both males and females. The function of dawn chorus in birds has been frequently interpreted according to seasonal variation of singing as the breeding season advances, but potential differences in seasonal variation of song and calls for the same species have not been taken into account.MethodsWe chose Dupont’s Lark as a model species to study whether the seasonal pattern of dawn chorus differs between singing and calling activity, because in this species most daily songs and calls are uttered at dawn. We registered vocal activity of Dupont’s Lark before and around dawn in three different populations, through repeated sampling over the entire breeding season of two consecutive years.ResultsWe found that dawn singing parameters remained constant or presented an increasing trend while dawn calling activity decreased as breeding season advanced. We also found different daily patterns for singing and calling, with birds calling mostly during the first 30 minutes of dawn choruses and singing peaking afterwards.DiscussionThe different time patterns of songs and calls may indicate that they serve diverse functions at dawn in the Dupont’s Lark. Relaxation of dawn calling activity after the first month of the breeding season would suggest that dawn calling may be mainly related to mate attraction, while constant dawn singing throughout the breeding period would support a relationship of dawn singing to territorial defence. Our study highlights that the type of vocalisation used is an important factor to consider in further research on dawn choruses, since results may differ depending on whether calls or songs are analysed.
Highlights
Dawn chorus occurs when birds, usually males, begin to sing before sunrise and cease or decrease song activity for the rest of the day (Mace, 1987; Catchpole & Slater, 2008, but see Garamszegi et al, 2006 and Webb et al, 2016 for female singing)
To understand dawn chorus in territorial birds, studies should account for: (1) the reason of the concentration of vocal activity at dawn, which has been explained by female behaviour, conditions for sound transmission and low foraging success at dawn, among others (Kacelnik & Krebs, 1983; Kunc, Amrhein & Naguib, 2005; Naguib et al, 2016), and (2) the function of the vocalisations uttered at dawn, which has been related to mate attraction (Eriksson & Wallin, 1986; Poesel et al, 2006; Murphy et al, 2008) and to territorial defence and mate guarding (Møller, 1988; Møller, 1991; Amrhein & Erne, 2006), the two functions can be complementary (Møller, 1991; Slagsvold, Dale & Sætre, 1994)
The only characteristic of singing activity related to the advance of the breeding season was singing output, since total number of songs uttered per male and night significantly increased in later surveys, while singing performance and singing start or ending time did not show a significant trend through surveys (Table 1, Fig. 3)
Summary
Dawn chorus occurs when birds, usually males, begin to sing before sunrise and cease or decrease song activity for the rest of the day (Mace, 1987; Catchpole & Slater, 2008, but see Garamszegi et al, 2006 and Webb et al, 2016 for female singing). Despite the prevalence of dawn-singing in birds and the numerous studies focused on that topic, its origin, evolution and causes remain unclear and seem to be contextdependent, differing among species, populations and studies (e.g., Staicer, Spector& Horn, 1996; Catchpole & Slater, 2008; Zhang, Celis-Murillo & Ward, 2016) This could be explained in part because researchers have indistinctly analysed or have even pooled calls and songs (Poesel, Foerster & Kempenaers, 2001; Grava et al, 2013; Stanley et al, 2016; Lee, MacGregor-Fors & Yeh, 2017) to elucidate dawn chorus function (but see LaZerte, Otter & Slabbekoorn, 2017). Our study highlights that the type of vocalisation used is an important factor to consider in further research on dawn choruses, since results may differ depending on whether calls or songs are analysed
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