Female song in birds is more widespread than previously thought but remains poorly studied. Relatively few researchers have compared the structure and function of female song with that of conspecific males, especially in non-duetting species. Here we investigate male and female song in the White-throated Dipper (Cinclus cinclus; hereafter 'Dipper'), a highly territorial and largely monogamous passerine with a complex song in both sexes. The songs of individually marked birds were recorded over a 3-year period in order to compare the acoustic structure and production of song in males and females at different stages of the breeding cycle. No differences were found in the complexity, frequency or temporal characteristics of male and female songs. However, unpaired males recorded early in the breeding season sang more complex songs than males that were paired up and nest-building or whose breeding attempts were underway, suggesting that male song is used for mate attraction. By contrast, females sang most often during aggressive encounters with birds from outside their territory. Furthermore, males sang throughout the breeding season, when they are highly territorial, whereas females rarely sang after laying had begun. Together, these results support findings from other species that song structure varies with context and suggest that female song in Dippers may be used primarily in mate or territory defence.
Capsule: Male White-throated Dippers Cinclus cinclus are more likely and quicker to respond to the playback of song than females, but both sexes are more likely to respond before the onset of breeding than after. Aims: Territoriality and the function of song in female birds have rarely been studied outside of the tropics or Australasia. We investigated territoriality and song function in males and females of a Northern temperate species, the White-throated Dipper. Methods: We conducted playback trials on established pairs and compared the responses of males and females according to the sex of the simulated intruder and the timing of playback relative to the onset of breeding. A response was classified as movement towards the speaker, singing or both. Results: Males were significantly more likely and quicker to respond to playback than females, but neither sex responded differently to the playback of male and female song. Both sexes were more likely to respond to playback before breeding had begun than after. Conclusions: Our results suggest that both males and females are territorial but that males take the dominant role in defence. Female song appears to elicit a similar response to male song and may play a role in territoriality or mate defence.
Capsule: Pairs of White-throated Dippers Cinclus cinclus which defended winter territories bred earlier than non-territorial individuals, but there was no difference in reproductive success. Aims:The effect of winter territoriality on breeding ecology has rarely been studied in resident birds. We carried out a preliminary investigation of whether winter territorial behaviour and territory size affect the timing of reproduction, breeding territory size and reproductive success in a riverine bird, the White-throated Dipper. Methods:We monitored an individually marked population of White-throated Dippers in the UK. Wintering individuals were classified as either territorial or 'floaters' according to their patterns of occurrence and behaviour, and their nesting attempts were closely monitored in the subsequent months. Winter and breeding territory sizes were measured by gently 'pushing' birds along the river and recording the point at which they turned back.Results: All birds defending winter territories did so in pairs, but some individuals changed partners before breeding. Territorial pairs that were together throughout the study laid eggs significantly earlier than pairs containing floaters and those comprising territorial birds that changed partners. However, there were no significant differences in clutch size, nestling mass or the number of chicks fledged. There was no relationship between winter territory length and lay date or any measure of reproductive success, although sample sizes were small. Winter territories were found to be significantly shorter than breeding territories. Conclusion:Winter territoriality may be advantageous because breeding earlier increases the likelihood that pairs will raise a second brood, but further study is needed. Territories are shorter in winter as altitudinal migrants from upland streams increase population density on rivers, but this may also reflect seasonal changes in nutritional and energetic demands.
Song complexity and singing frequency in male birds are shaped by female choice; they signal male quality because song is costly to develop and produce. The timing of song learning and the development of the brain structures involved occur during a period when chicks are exposed to a number of potential stressors. The quality and quantity of song produced by adults may therefore reflect the level of stress experienced during early life, a theory known as the ‘developmental stress hypothesis’. We tested this hypothesis using song recordings and life-history data from an individually marked, long-term study population of wild dippers (Cinclus cinclus). The extent to which early life conditions predict adult song traits was investigated using natal brood size as a measure of sibling competition; the rate of provisioning by parents as a proxy for nutritional stress; and residuals of the linear regression between body mass and tarsus length as a measure of nestling condition. The syllable diversity in the songs of adult males was positively correlated with their body condition as nestlings, but there was no significant correlation with either provisioning rate or brood size. Provisioning rate did, however, predict song rate; males in relatively poor condition as nestlings or those raised in smaller broods which were fed more frequently by their parents sang at a higher rate in adulthood. These results support the developmental stress hypothesis and provide some of the first evidence from a wild bird of how the conditions experienced during early life impact adult song. Song traits may therefore provide females with information regarding both the current condition and developmental history of males.
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