THE COST OF DOMINANCE AND ADVANTAGE OF SUBORDINATION IN A BADGE SIGNALING SYSTEM.

Reliable signals of social status are a seeming paradox. High social status often confers survival or reproductive advantages; therefore, we ask why low-ranked individuals do not display signals of high status, thus deceptively increasing their potential for survival or reproduction. Such deceptions would undermine the reliability of a signal. Therefore, to explain the meaningfulness of conventional signals of social status we must explain either why cheaters do not successfully invade a population of signalers or why cheaters are held at a low frequency. By definition, cheaters are individuals that communicate inaccurate information that is potentially beneficial to them (in this case about status) when they are capable of communicating more accurate information without undue costs. Including in this definition the capacity to communicate more accurate information distinguishes cheating from the transfer of misinformation through error or ignorance. This definition neither requires cheating to be a conscious act nor excludes this possibility. Signals of social status lie on a cost continuum; contributing costs include those of sending, generating, wearing, or transporting the indicator of status. Costly signs of status are difficult to mimic; consequently, the evolutionary stability of costly indicators of status is not perplexing (Zahavi, 1977). Some likely examples of costly signs of states are (1) the massive horns and antlers of artiodactyls (Geist, 1966a, 1966b), which are expensive to generate and to carry about; (2) the low pitch of toad calls (Bufo bufo), which cannot be mimicked because the low croaks of dominant individuals are physically dependent on having a big body (Davies and Halliday, 1978); and (3) the roaring of red deer (Cervus elaphus), which is expensive because roaring is exhausting (CluttonBrock and Albon, 1979). In contrast, the bib and crown coloration of winter Harris' sparrows (Zonotrichia querula) is a signal of low cost. Individuals with more black feathering on their bib and crown dominate those with less black feathering, and escalated contests over status or resources are rare (Rohwer, 1975, 1977). Because of its low cost and symbolic nature the Harris' sparrow signal seems easily faked; appropriately, Dawkins and Krebs (1978) call it a badge. In this paper we ask "How can badges of status be evolutionarily stable?" Investigating the evolutionary stability of a badge presupposes that color differences among individuals do signal dominance status. This view has been challenged by Baker and Fox (1978), Balph et al. (1979) and Shields (1977), but supported by Ketterson (1979a). For Harris' sparrows the status signaling hypothesis has been bolstered by data showing that variation in appearance within age and sex classes is significantly associated with status under certain resource distributions (Rohwer et al., unpubl.). Understanding how badges of status are evolutionarily stable (Maynard Smith, 1976) requires explaining why subordinates signal their low rank. To answer this question we have concentrated on answering a subsidiary question, namely, "Why should dominant and subordinate phenotypes coexist in the same flock?" This question is meaningful only when dominance status is measured by some characteristic of individuals that will apply from flock to flock. Traditionally dominance status has been defined as an individual's rank in the hierarchy of its own