Abstract
BackgroundThe vocalizations of birds are dynamic traits that often vary in output with time of day and time of year. By quantifying patterns of diel and seasonal variation in vocal output, we can gain insight into the ecology and evolution of birds and the function of their vocalizations. In this investigation, we quantified diel and seasonal variation in song output by studying a breeding population of Savannah Sparrows (Passerculus sandwichensis).MethodsWe used autonomous recorders to collect extensive recordings across the breeding season in a long-term, colour-marked study population of Savannah Sparrows in eastern Canada. We described diel and seasonal variation across five different breeding stages based on recordings of more than 50,000 songs from 34 males.ResultsDuring the pre-breeding stage, prior to female arrival, males sang a pronounced dawn chorus with a peak in song output during the early morning. During the breeding stage, in contrast, the dawn chorus was diminished and males instead exhibited a pronounced dusk chorus with a peak in song output during the evening. Across the breeding season, the highest levels of song output occurred in late April and early May, soon after males arrived on the breeding grounds, and the lowest levels occurred in August, prior to the departure of birds for the wintering grounds.ConclusionsThese patterns suggest that Savannah Sparrows’ early-season dawn choruses are directed at males and serve a territorial defense function. Later-season dusk choruses, in contrast, appear to play a role in attracting mates and possibly acoustic mate guarding.
Highlights
The vocalizations of birds are dynamic traits that often vary in output with time of day and time of year
Based on analysis of 58,301 songs from 34 male Savannah Sparrows recorded during a 5-month time span, we found substantial variation in song output, both with time of year (Fig. 2a) and with breeding stage (Fig. 2b)
We analyzed variation in song output on an hourly basis, and found that song output varied with time of day (LMM: F19,132 = 10.1, p < 0.0001); song output showed no systematic variation with breeding stage (F4,132 = 0.1, p = 0.98); song output varied with the interaction between time of day and breeding stage (F76,132 = 6.9, p < 0.0001); and song output varied between males
Summary
The vocalizations of birds are dynamic traits that often vary in output with time of day and time of year. By quantifying patterns of diel and seasonal variation in vocal output, we can gain insight into the ecology and evolution of birds and the function of their vocalizations In this investigation, we quantified diel and seasonal variation in song output by studying a breeding population of Savannah Sparrows (Passerculus sandwichensis). Songbirds are well known for their dawn choruses, and to a lesser degree their dusk choruses They provide a model system in the field of acoustic communication to study diel variation in vocal output (Staicer et al 1996)
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