Status signaling is absent within age-and-sex classes of Harris' sparrows

-We tested the status-signaling hypothesis in two groups of same-age and samesex Harris' Sparrows (Zonotrichia querula). Unlike flocks of mixed age and sex composition, badge size did not correlate with social status in these groups; thus, status signaling does not appear to occur within age-and-sex classes of Harris' Sparrows. Other predictions of the status-signaling hypothesis we tested were that (1) fighting ability and social status should be correlated, and (2) fighting ability and badge size should be correlated. We used a multivariate assessment of body size as an indicator of fighting ability and found no support for either prediction in the flock of adult females. In the flock of adult males, large birds were more dominant (Prediction 1) but fighting ability and badge size were not correlated (contra Prediction 2). Received 21 May 1987, accepted 20 January 1988. THE status-signaling hypothesis, invoked to explain avian winter plumage variability (Rohwer 1975), comprises three relationships: (1) Individuals with superior fighting ability are able to defeat a greater number of opponents than individuals with inferior fighting ability. Good fighters therefore have higher social status than poor fighters (relationship A, Fig. 1). (2) Individuals should signal their fighting ability to other individuals (relationship B, Fig. 1). If good fighters can be recognized, they will be avoided by other birds and will gain resources without being contested. Individuals with inferior fighting ability do not cheat (i.e. display badges like those of better fighters) because they benefit either by associating with better fighters or by employing an alternative competitive strategy. Reliably signaling their ability and assuming a subordinate role presumably results in a higher payoff than cheating (Rohwer and Ewald 1981, Rohwer 1982). (3) Given the first two relationships, there should be a positive correlation between social status and the conspicuousness of the badge (relationship C, Fig. 1). The status-signaling hypothesis has been analyzed in nine species and the results reviewed recently by Whitfield (1987). Plumage differences are often correlated with sex and age, so unless these correlated traits are controlled, it is unclear whether badges function as status signals within groups of same-sex and same-age individuals. Only two studies, on Great Tits (Parus major; Jarvi and Bakken 1984) and Pine Siskins (Carduelis pinus; Balph and Balph 1979), support the hypothesis fully by showing that plumage is correlated with social status even among birds of the same age and sex. We investigated the status-signaling hypothesis in Harris' Sparrows (Zonotrichia querula) by examining dominance relationships among individuals of the same age and sex classes. We wanted to correlate social status and intrinsic fighting ability in controlled age and sex populations. We assumed that body size is a determinant, or at least an indicator, of fighting ability. If body size affected social status, then we predicted larger birds would have badges that were more conspicuous than those of smaller birds. The badge displayed by Harris' Sparrows, a black crown and bib on the throat and breast, varies among age-and-sex classes from being almost completely absent to covering almost all of this area. Badge size varies much less within age and sex classes. If better fighters are higher in status and and have larger badges, then we would expect a correlation between social status and badge size within these groups of same ageand-sex individuals. Rohwer (1985) showed that young birds dyed to resemble adults obtained higher social status than control birds within flocks of young males and young females. This demonstrated that status signaling occurs between age classes, and therefore cannot answer the questions posed here because badge size is correlated with age (Rohwer et al. 1981).