• Naguib, Marc
  • Mennill, Daniel J.


Birdsong is among the most well-studied communication systems in vertebrates and provides many textbook examples in animal behaviour, ecology and evolution. Owing to the substantial body of research dealing with this topic, and the numerous research groups focusing on different aspects of birdsong, it is often difficult to maintain an overview across the discipline. An increasing number of reviews on various aspects of birdsong provide important syntheses (Todt & Naguib 2000; Vehrencamp 2000; Gil & Gahr 2002; Beecher & Brenowitz 2005; Catchpole & Slater 2008). The recent review by Searcy & Beecher (2009) makes a valuable contribution by bringing together a substantial body of research on the territorial function of birdsong with a specific focus on singing contests. The review covers a large body of research and critically discusses the evidence that certain components of singing contests act as aggressive signals. Furthermore, it places many ideas in a context that will stimulate researchers to conduct more advanced studies and to plan carefully which behavioural responses to measure. While reviewing the literature on the signal value of various communication strategies, Searcy & Beecher (2009) discuss song overlapping, a well-studied component of singing contests. They conclude that song overlapping may not be a signal at all, despite a large body of research which argues to the contrary. Here we complement the valuable review of Searcy & Beecher (2009) by providing a different view on how to evaluate the traits that are components of animal signalling interactions. We focus on song overlapping because it is among the best studied traits in the territorial interactions of songbirds, because it is well studied in other taxa including anurans and insects (Grafe 1999; Gerhardt & Huber 2002), and because Searcy & Beecher (2009) discuss overlapping from a perspective we do not share