Multi-functional crest display in hoopoes Upupa epops

Animals can engage in visual displays, which may target conspecifics, heterospecifics or both. Here we studied the function of the flamboyant crest-raising display of hoopoes (Upupa epops) in experiments performed with males in captivity. Males were exposed to sounds of a conspecific (male hoopoe song), a potential predator (human voice), and two controls (the song of a blackbird, Turdus merula, and background noise). These stimuli were presented to males in the presence and absence of females. Males raised the crest with a significantly higher probability when confronted with stimuli indicating potential threats (rival mate or predator) than with controls. The crest display was frequent when confronted with both kinds of threats independently of the presence of a female, suggesting that it was directed to the predator and the rival male. The probability of raising the crest was not related to body condition, and there was a marginally but not significant negative relationship between p...