RESEARCH PAPER White Flank Spots Signal Feeding Dominance in Female Diamond Firetails, Stagonopleura guttata Clare J. Crowhurst*, Valeria Zanollo*, Matteo Griggio , Jeremy Robertson* & Sonia Kleindorfer* * School of Biological Sciences, Flinders University, Adelaide, SA, Australia  Department of Integrative Biology and Evolution, Konrad Lorenz Institute for Ethology, University of Veterinary Medicine, Vienna, Austria Introduction Darwin (1871) proposed the theory of sexual selec- tion to explain the evolution of ornamentation and other secondary sexual characters that did not appear to contribute to survival. Despite the wide- spread occurrence of female ornamentation, most sexual selection researchers have concentrated on male secondary sexual characters (reviewed in Clut- ton-Brock 2007). There is a need for more research into female ornamentation, rather than a narrow focus on female intrasexual competition in polyan- drous species (Amundsen 2000; Clutton-Brock 2007, 2009). The ornamented females that have been stud- ied have shown high levels of intrasexual competi- tion, suggesting that female ornamentation primarily functions in intraspecific competition in the defence of resources or territories, favoured by maternal investment and strong fecundity selection in females (West-Eberhard 1983; Clutton-Brock et al. 2006; Le- Bas 2006; Clutton-Brock 2009). While the function of signals shaped by sexual selection is to attract mates or drive off rivals, these signals may also evolve through social selection, in which the social context influences the fitness of sig- nallers and receivers (West-Eberhard 1983; Tanaka Correspondence Valeria Zanollo, Flinders University of South Australia, School of Biological Sciences, Bedford Park, Adelaide, SA 5042, Australia. E-mail: zano0006@flinders.edu.au Received: July 12, 2011 Initial acceptance: August 13, 2011 Final acceptance: October 19, 2011 (L. Fusani) doi: 10.1111/j.1439-0310.2011.01986.x Abstract Plumage colour can be used as an honest signal to convey health and status, which has traditionally been examined in the sexual selection context of choosy females and elaborate males. We use a model avian system to study the role of plumage coloration in a social context such as inter- and intrasexual competition over food resources. The diamond firetail (Stagonopleura guttata) is an endemic Australian finch: females have more white flank spots than males, and white spot number was correlated with cell-mediated immune response in females. We use two experimental designs to test the role of white flank spots for feeding dominance and dominance discrimination in a group-living bird. The results from two-choice trials and from single-arena trials showed that female ornamentation was consistently important in social food contests, and males consistently responded to female spot number. Females with higher spot number fed first, in trials with males and ⁄ or females. Also, females preferred to feed next to test birds with low spot number, but males showed no preference for feeding next to birds with few or many spots. Finally, latency to feed was predicted by spot number: both males and females had longer latency to feed if test birds had more spots than the focal birds. We conclude that female, but not male, ornamentation was important for inter- and intrasexual food competition. This is one of the very few studies to show that the same plumage ornament can have a different function between the sexes as a signal of social status. More- over, this study shows that white plumage can be a signal of dominance. Ethology Ethology 117 (2011) 1–13 ª 2011 Blackwell Verlag GmbH 1