Bottoms up: great bustards use the sun to maximise signal efficacy

Visual displays are signals that may be selected to increase visibility. Light is a crucial component in the transmission of visual signals, and white colour is very conspicuous when illuminated by sun and exhibited against darker backgrounds. Here we tested the hypothesis that orientation of sexual displays in male great bustard (Otis tarda) depends upon position of the sun, i.e., males direct their uplifted white tails towards the sun in order to maximise signal detectability to distant females. We recorded the orientation of 405 male displays in relation to the sun and to females at seven leks. Great bustard males signalled towards the sun more often than expected by chance in early morning, although this pattern was not obvious at other times of day, when males displayed more towards females. Our hypothesis was further supported by the fact that displays were more directed towards the sun when the sun was most visible. Males were more likely to direct their displays towards females during the most elaborate components of their courtship display and when there were fewer males on the lek. Pointing white plumage to the sun may be a behaviour selected in species living in steppe-like open landscapes if individuals obtain net fitness benefit by increasing the likelihood of mating.P.P.O. was partially supported by research project from the Ministerio de Educación y Ciencia (CGL2006-05047/BOS). F.C. was supported by a postdoctoral grant funded by the regional government of Castilla la Mancha (JCCM).Peer reviewe