Non-Breeding Song Rate Reflects Nutritional Condition Rather than Body Condition

Johan J Bolhuis,Marcel Eens,Alain J.-M Van Hout,Ann Geens,Rianne Pinxten

doi:10.1371/journal.pone.0036547

Abstract

Numerous studies have focused on song in songbirds as a signal involved in mate choice and intrasexual competition. It is expected that song traits such as song rate reflect individual quality by being dependent on energetic state or condition. While seasonal variation in bird song (i.e., breeding versus non-breeding song) and its neural substrate have received a fair amount of attention, the function and information content of song outside the breeding season is generally much less understood. Furthermore, typically only measures of condition involving body mass are examined with respect to song rate. Studies investigating a potential relationship between song rate and other indicators of condition, such as physiological measures of nutritional condition, are scant. In this study, we examined whether non-breeding song rate in male European starlings (Sturnus vulgaris) reflects plasma metabolite levels (high-density lipoproteins (HDL), albumin, triglycerides and cholesterol) and/or body mass. Song rate was significantly positively related to a principal component representing primarily HDL, albumin and cholesterol (and to a lesser degree plasma triglyceride levels). There was only a trend toward a significant positive correlation between song rate and body mass, and no significant correlation between body mass and the abovementioned principal component. Therefore, our results indicate that nutritional condition and body mass represent different aspects of condition, and that song rate reflects nutritional rather than body condition. Additionally, we also found that intra-individual song rate consistency (though not song rate itself) was significantly positively related to lutein levels, but not to body mass or nutritional condition. Together our results suggest that the relation between physiological measures of nutritional condition and song rate, as well as other signals, may present an interesting line of future research, both inside and outside the breeding season.

Highlights

Numerous studies have focused on the information content of animal signals, in birds species [1,2]
Bird song has received much attention from researchers as a signal involved in mate choice and intrasexual competition [3,4,5,6,7]
A linear regression model for body mass showed no significant effect of the PC (b = 0.262, p = 0.12)

Summary

Introduction

Numerous studies have focused on the information content of animal signals, in birds species [1,2]. While a fair number of studies have examined seasonal variation in bird song and its neural substrate [8,9], and for some species, such as the European starlings (Sturnus vulgaris), much progress has been made in understanding the underlying neural and hormonal mechanisms [10,11,12], the function and information content of non-breeding song has received little attention and is generally much less understood [13]. Understanding the information content of non-breeding song may prove essential to form an integrated picture of seasonal variation in the expression and physiological control of song as a signal

Methods

Results

Conclusion