Status signalling, metabolic rate and body mass in the siskin: the cost ofbeing a subordinate

The higher metabolic rate of dominant individuals, found in different speci es, has been interpreted as the cost that prevents subordinates from cheati ng by adopting large badges of status. However, an alternative prediction f or status-signalling species, in which subordinates may recognize dominants , is that subordinates have the higher metabolic rate because of the greate r stress of locating and actively avoiding aggressive interactions with the m. In this study, the size of the black bib of the siskin, Carduelis spinus , which is a badge of dominance, was negatively correlated with metabolic r ate in daylight, even when controlling for the bird's activity level in the respirometer chamber and its body mass. The size of the black bib, however , was not correlated with metabolic rate in darkness. This suggests that th e difference between dominance classes is not related to intrinsic physiolo gical differences, but that subordinates are more susceptible to stressful conditions. When controlling for metabolic rate, a positive correlation app eared between dominance status and body mass. This stresses the importance of knowing the effects of social status on energy requirements for understa nding the relationship between body mass and dominance. We conclude that ma intaining a high social status may be more stressful to subordinates than t o dominant birds. (C) 2000 The Association for the Study of Animal Behaviou r.