Signaling of need, sibling competition, and the cost of honesty

Young birds and mammals frequently solicit food by means of extravagant and apparently costly begging displays. Much attention has been devoted to the idea that these displays are honest signals of need, and that their appare nt cost serves to maintain their honesty. Recent analyses, however, have sh own that the cost needed to maintain a fully informative, honest signal may often be so great that both offspring (signaler) and parent (receiver) wou ld do better to refrain from communication. This apparently calls into ques tion the relevance of the costly signaling hypothesis. Here, I show that th is argument overlooks the impact of sibling competition. When multiple sign alers must compete for the attention of a receiver las is commonly the case in parent-offspring interactions), I show that tall other things being equ al) individual equilibrium signal costs will typically be lower. The greate r the number of competitors, the smaller the mean cost, though the maximum level of signal intensity employed by very needy signalers may actually inc rease with the number of competitors. At the same time, costs become increa singly sensitive to relatedness among signalers as opposed to relatedness b etween signalers and receivers. As a result of these trends, signaling prov es profitable for signalers under a much wider range of conditions when the re is competition (though it is still likely to be unprofitable for receive rs).