Abstract
In breeding plumage, the African male red-shouldered widowbirds (Euplectes axillaris) are black except for red carotenoid-based epaulets ('shoulder patches'), similar to the well-studied American red-winged blackbirds (Agelaius phoeniceus). To experimentally test the signal function of the red epaulets in male red-shouldered widowbirds, we manipulated epaulet colour and size (within natural variation), and observed the effects in two competitive contexts. First, in captivity, unfamiliar males with epaulets of different size or redness were staged in dyadic contests over food. Only epaulet manipulations significantly affected contest outcome; red epaulet males out-competed orange and control males, which in turn dominated blackened (no epaulet) males. Epaulet size manipulations had particularly strong effects; enlarged epaulet males vigorously defeated smaller epaulet males within colour treatments, whereas the independent effect of 'redness' (i.e., within size treatments) was much weaker. Second, in a field experiment, epaulets were manipulated prior to territory establishment. Males with enlarged epaulets acquired territories, whereas most males with blackened or reduced signals failed to obtain territories. Furthermore, among the territorial males, birds with enlarged epaulets defended larger territories and spent less time in boundary signalling, yet they received fewer intrusions from conspecifics. In contrast, epaulet manipulations had no effect on either female visitation rates or subsequent female settlement. These results concur with recent studies and suggest that the carotenoid-based epaulets of red-shouldered widowbirds are status signals, sexually selected through male contest competition for territories.
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Acknowledgements
Thanks to the owners and managers of Tschonga Farm for allowing us to work on their land, and to Malte Andersson and two anonymous referees who provided helpful comments on the manuscript. Permission to collect, house (permit no. 28562/2001) and work with wild red-shouldered widowbirds (permit no. 28561/2001) was granted by the KwaZulu-Natal Wildlife Services, and all experimental work was approved by the University of Natal's Animal Ethics Committee (reference no. AE/01/10). Funding was provided by the Swedish Science Council (to S.A.) and an academic exchange program from the Swedish STINT foundation (to S.P.)
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Pryke, S.R., Andersson, S. Carotenoid-based status signalling in red-shouldered widowbirds (Euplectes axillaris): epaulet size and redness affect captive and territorial competition. Behav Ecol Sociobiol 53, 393–401 (2003). https://doi.org/10.1007/s00265-003-0587-2
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DOI: https://doi.org/10.1007/s00265-003-0587-2