Plumage colour saturation predicts long-term, cross-seasonal social dominance in a mutually ornamented bird

Dominance hierarchies are known to reduce agonistic interactions between individuals and may be influenced by differences in phenotypes such as body size, personality or cognition. Colour ornamentation, especially with melanin-based colours, can also be a badge of status signalling social dominance, but status signalling with carotenoid-based colours is little understood. Here we studied whether different phenotypes, including individual differences in carotenoid-based colour ornamentation, body size, personality-, cognition- and stress-related traits, predict social dominance in the highly social and mutually ornamented common waxbill, Estrilda astrild. We monitored aggressive interactions of waxbills living in seminatural conditions, in a large mesocosm, using data from a radiofrequency identification system in the nonbreeding and breeding seasons over 2 consecutive years. We found the position of individual waxbills in the dominance hierarchy repeatable across seasons and years. Furthermore, the steepness of the dominance hierarchy was greater in the breeding seasons, perhaps because of increased competition over mates or breeding resources. Contrary to previous work with waxbills in birdcages, here body size did not predict social dominance, perhaps because in our more natural setting aggressive encounters were mostly airborne, where large body size may not confer a fighting advantage and may even reduce manoeuvrability. Sex, reactive-to-proactive personality differences and traits related to cognition or stress did not predict social dominance either. Finally, red colour saturation, but not the size of the red patch, strongly predicted social dominance and may thus act as a badge of status. This is one of the few studies testing whether size or saturation of carotenoid-based plumage coloration indicates social dominance and suggests that saturation may more often signal dominance. (c) 2021 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.