Reliability of low-amplitude signals
A reliable signal is one that accurately represents the intrinsic quality or state being advertised by the signaller (Maynard Smith and Harper, 2003 and Searcy and Nowicki, 2005). Reliable signals present a puzzle whenever there is a conflict of interest between signaller and receiver, for example, rivals contesting a resource, or siblings competing for parental care. Such conflicts lead to selection that favours signallers that cheat or bluff in order to manipulate receivers to their own advantage (Dawkins & Krebs, 1978). Despite this AZ3146 expected selection for dishonesty in signalling, research has shown that signals are reliable enough of the time that both signallers and receivers benefit from the communication system (Maynard Smith and Harper, 2003 and Searcy and Nowicki, 2005).
Two general mechanisms hypothesized to explain reliability in acoustic signals are production costs and physical constraints (reviewed in Hurd and Enquist, 2005, Maynard Smith and Harper, 2003, Searcy and Nowicki, 2005 and Vehrencamp, 2000). Production costs act as ‘handicaps’ that make bluffing too costly for lower-quality signallers (Grafen, 1990, Zahavi, 1975 and Zahavi, 1977). Physical constraints arise from a link between some signal feature and some physical characteristic of the signaller. These ‘index’ signals cannot be faked or exaggerated by lower-quality individuals because chitin are physically constrained from doing so (Maynard Smith & Harper, 2003).