Why are females ornamented? A meta-analysis and case study

Female ornaments are often expressed as reduced male-like ornaments. Although they were once considered non-functional by-products of selection acting on males, recent evidence suggest that they can act as signals under sexual and social selection. Nevertheless, it is unclear whether signalling functions are widespread in females, and how signalling might be affected by the tendency for reduced elaboration. I review and meta-analyse studies across mutually ornamented birds and investigate female ornaments in purple-crowned fairy-wrens Malurus coronatus. My findings suggest that, despite few exceptions, ornaments may be widely acting as signals in females as they do in males.