Maximizing sexual signal transmission: use of multiple display sites by male houbara bustards

Abstract

Abstract A good location of song or call posts and visual display sites of males is crucial for territory defence and mate attraction. These sites are typically located at prominent positions to ensure an efficient, long-distance sexual advertisement. If the purpose of display sites is to maximize visibility, a suitable strategy would be to use multiple display sites rather than just one site. We investigated this in the ground-displaying houbara bustard by using two recent technological advances that enabled us collecting high precision data, GSM/GPRS loggers provided with accelerometer and very high-resolution digital elevation models of the terrain. We found that 12 out of 20 marked males used two or three display sites instead of just one as previously assumed in this species. The most used display site had the largest viewshed and use of both alternative sites decreased in proportion to their decreasing viewsheds. The number of display sites was apparently determined by two factors. First, it was correlated with display intensity, suggesting that using multiple display sites may be a mechanism to increase sexual signal transmission in males that are dominant or in better condition. Second, supplementary display sites were not used when the principal display site already provided an excellent view of the surroundings, e.g. when it was located on a hilltop. These results confirmed that the function of secondary display sites is to supplement the viewshed provided by the principal display site, and so maximize sexual signal transmission. Significance statement Performing sexual display from just a single place is often not enough to reach all possible mates or competitors, so using multiple posts may be crucial for an effective sexual signal transmission. This is particularly important when the display is visual, and topographical barriers or vegetation may block the male’s line of view. Using last generation GSM/GPRS loggers equipped with accelerometers and very high-resolution digital elevation models of the terrain, we show how houbara bustard males, who perform a costly running display on the ground, have developed a complex display pattern that involves the use of various nearby display sites. These display sites are used in proportion to their visibilities, which shows that this multiple display site system has evolved to maximize the aggregated visual field of males and so increase their visibility to females and neighbour males.