Anim. Behav., 1997, 54, 1205–1214 The role of bright plumage in male–male interactions in the ring-necked pheasant CONCHA MATEOS & JUAN CARRANZA Biology and Ethology Unit, University of Extremadura ( R eceived 30 M ay 1996; initial acceptance 31 July 1996; final acceptance 18 February 1997; M S. number: 5237) Abstract. The brightness and colour of birds’ plumages have been considered sexually selected traits, indicating health, condition or parasite resistance. However, recent studies with pheasants, Phasianus colchicus, suggest they are not signals used by females in mate choice. Instead, males might rely on plumage when assessing the quality of competitors. In this study, bright and experimentally dulled males were presented to a group of captive male pheasants to determine the response to differences in plumage brightness of the intruder. Males in the group directed more aggression to the experimentally dulled males than they did to any other males. This may be partly because they considered the dull males as novel males. When the bright and the dull males were both unknown, both still received more aggression than the average for any individual in the group, but dull males were attacked by more males. Bright males were attacked more by the dominants and dull males by the subordinates. The results show that plumage brightness may a ffect individual recognition, but also that it is used by males to assess the quality of competitors. Male–male interactions, therefore, may have played a role in the evolution of plumage brightness, either in the context of competition for mates or for resources when males gather into unisexual groups.  1997 The Association for the Study of Animal Behaviour The adaptive function of sexual dimorphism of some bird plumages, and their possible evolution- ary origin and maintenance, remain contentious. Although several hypotheses may provide alterna- tive explanations (see reviews in Butcher & Rohwer 1989; Andersson 1994), it is generally assumed that mate choice and contest competition may be important selection factors for many conspicuous and coloured bird plumages. On the one hand, plumages of males might indicate health, condition, parasite resistance or ability to acquire resources, thus providing potential cues in female mate choice (e.g. Andersson 1982; Hamilton & Zuk 1982; Grafen 1990; Hill 1991). On the other hand, males might rely on plumage when assessing the quality of competitors. Many studies on bird plumages indicate that selection for male competitive ability and aggression might favour the evolution of conspicuous conventional signals or ‘badges’ of status in male plumages (Rohwer 1977, 1982; Rohwer & Ewald 1981; Studd & Robertson 1985; Evans & Hatchwell 1992; Guilford & Dawkins 1995). Recent studies on Galliformes confirm that females prefer less parasitized, more resistant males (e.g. Hillgarth 1990; Zuk et al. 1990a ), but do not seem to indicate that the signals used in female choice were the colour and brightness of the male plumage (red junglefowl, Gallus gallus spadiceus: Zuk et al. 1990b ; Ligon & Zwartjes 1995; wild turkey, M eleagris gallopavo: Buchholz 1995) and the same applies to the ring- necked pheasant, Phasianus colchicus (Mateos & Carranza 1995). For this species, we already know that some male ornaments, such as the red wattles, and even the small feathers in the ear tufts, are signals on which males rely during agonistic contests (Mateos & Carranza 1997). Similarly, other plumage features, such as bright- ness, might be used by males to indicate the quality of the opponent. Male ring-necked pheasants are polygynous, defend mating territories and do not contribute to parental care. Male competition to acquire territories is quite high (Cramp & Simmons 1980; Hill & Robertson 1988; Biadi & Mayot 1990). Correspondence: C. Mateos, Ca ´tedra de Biologı ´a y Etologı ´a, Facultad de Veterinaria, Universidad de Extremadura, 10071 Ca ´ceres, Spain (email: cmateos@ unex.es). 0003–3472/97/111205+ 10 $25.00/0/ar970516  1997 The Association for the Study of Animal Behaviour 1205