Ornamental plumage does not signal male quality in red-billed queleas.

Abstract

Sexually selected ornaments often function as condition-dependent signals of quality (or 'indicators'). When ornamentation is costly, only high-quality individuals can afford to produce the most elaborate signals. The plumage ornamentation of male red-billed queleas, Quelea quelea, is an ideal candidate for an indicator because it is continuously variable, conspicuous, sexually dimorphic, is displayed only during breeding and is partially based on carotenoid pigmentation. However, I show here that quelea plumage is not an indicator because first, plumage colour is not correlated with physical condition or age; second, plumage colour is a genetically determined phenotype that is unresponsive to environmental variation; third, different plumage characters have bimodal distributions; fourth, plumage characters vary independently of one another; and finally, plumage colour is not correlated with reproductive success. To my knowledge, this is the first demonstration of non-condition dependence in colourful and sexually dimorphic breeding ornamentation. Instead, plumage variation may function as a sexually selected signal of individual identity among territorial males that nest in huge, densely packed and highly synchronized colonies.