Abstract
The status signalling hypothesis aims to explain within-species variation in ornamentation by suggesting that some ornaments signal dominance status. Here, we use multilevel meta-analytic models to challenge the textbook example of this hypothesis, the black bib of male house sparrows (Passer domesticus). We conducted a systematic review, and obtained primary data from published and unpublished studies to test whether dominance rank is positively associated with bib size across studies. Contrary to previous studies, the overall effect size (i.e. meta-analytic mean) was small and uncertain. Furthermore, we found several biases in the literature that further question the support available for the status signalling hypothesis. We discuss several explanations including pleiotropic, population- and context-dependent effects. Our findings call for reconsidering this established textbook example in evolutionary and behavioural ecology, and should stimulate renewed interest in understanding within-species variation in ornamental traits.
Highlights
Plumage ornamentation is a striking example of colour and pattern diversity in the animal kingdom, and has attracted considerable research (Hill, 2002)
Many studies have suggested that bib size serves as a badge of status, but most studies are based on limited sample sizes, and have used inconsistent methodologies for measuring bib and dominance status (Nakagawa, Ockendon, Gillespie, Hatchwell, & Burke, 2007; Santos et al, 2011)
Our findings call for reconsidering this textbook example in evolutionary and behavioural ecology, and should stimulate renewed attention to hypotheses explaining within-species variation in ornamentation
Summary
Plumage ornamentation is a striking example of colour and pattern diversity in the animal kingdom, and has attracted considerable research (Hill, 2002). Aggressive contests are costly in terms of energy use, and risk of injuries and predation (Jakobsson, Brick, & Kullberg, 1995; Kelly & Godin, 2001; Neat, Taylor, & Huntingford, 1998; Prenter, Elwood, & Taylor, 2006; Sneddon, Huntingford, & Taylor, 1998) These costs could be reduced if individuals can predict the outcome of such contests beforehand using so-called “badges of status” – i.e. two potential competitors could decide whether to avoid or engage in aggressive interactions based on the message provided by their opponent’s signals (Rohwer, 1975). Many studies have suggested that bib size serves as a badge of status, but most studies are based on limited sample sizes, and have used inconsistent methodologies for measuring bib and dominance status (Nakagawa, Ockendon, Gillespie, Hatchwell, & Burke, 2007; Santos et al, 2011)
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