Is male condition corrected with song features in Dusky Warblers (Phylloscopus fuscatus)

Background Birdsong is an important form of communication that plays an important role in territorial defense and mate attraction by conveying valuable information. While body-size and song frequency are often negatively correlated among species, this relationship is only found in a few songbirds. Previous studies on the Dusky Warbler (Phylloscopus fuscatus) found that there was a positive correlation between tarsus length and peak frequency. And heavier male Dusky Warblers possess better territories and obtain more opportunities for mating; body condition may be related to reproduction of birds, so females may choose heavier mates or better body condition based on the singing characteristics of males.

Methods We recorded spontaneous song and measured morphology of 33 male Dusky Warblers in Saihanba Forest Farm area between July 5 and August 10, 2015. We chose body weight as an indicator of body size and defined body condition as residuals from a linear regression between body weight and tarsus length. Frist, we used Pearson correlation to analyze whether date and time of day were correlated with weight, and then we used linear regression to analyze whether sound features could indicate the body weight and body condition. We call body weight and body condition the male condition.

Results We found no effect of date and time of day on weight, and we showed a correlation between the male condition and song features in the small songbird, Dusky Warbler. Maximum trill quality and maximum peak frequency of songs were negatively related to male condition; the mean number of syllables of songs and maximum high frequency of songs were positively correlated with body weight and body condition.

Conclusions In the small songbird, Dusky Warbler, four song parameters, including maximum trill quality, mean number of syllables of songs, maximum peak frequency of songs, maximum high frequency of songs, significantly predicted male condition change of which the most important song characteristic for male condition was maximum trill quality. This study suggested that the extreme song features were more constrained by male condition than mean sound characteristics.