Physiological costs and age constraints of a sexual ornament: an experimental study in a wild bird

Abstract Sexual ornaments are often considered honest signals of quality because potential costs or constraints prevent their display by low-quality individuals. Testing for physiological is difficult, as this requires experimentally forcing individuals to produce and elaborate ornaments. We use approach test whether a sexually selected trait physiologically costly male superb fairy-wrens (Malurus cyaneus). Male molt from brown blue breeding plumage at different times the year, females strongly prefer few males that early, during winter. used short-acting testosterone implants stimulate “early-blue” assessed after using panel indices. Testosterone-implanted, T-males molted in winter produced 6 weeks before control-implanted, C-males. while lower body condition, tended have fat reserves, were more likely be parasitized lice. However, we detected no negative effects on immune function, blood parasites, exposure stressors, survival. Juvenile never naturally early-blue plumage, but found evidence increased paid juvenile T-males. Instead, later than adult T-males, suggesting age presents an absolute constraint ornament exaggeration cannot fully overcome treatment. Together, these small large, age-related may enforce signal honesty, explain female preference males.