Displaying to females may lower male foraging time and vigilance in a lekking bird

Abstract

Males of many species use courtship behavior to attract mates. However, by doing so males may face the associated costs of increased energetic expenditure, reduced foraging time, and elevated predation risk. We investigated the costs of display in lekking male Sharp-tailed Grouse (Tympanuchus phasianellus). We used lek-wide scan sampling to study how males allocated time among courtship display (''dancing''), agonism, foraging, and inactivity in relation to female numbers both within and across days. We also addressed the limited attention hypothesis and estimated visual attentiveness by videotaping 13 males and scoring head turns during these different activities. We found that the proportion of males engaged in display increased significantly with female numbers both within and across days. Additionally, foraging decreased with increasing female numbers both within and across days. Our results also suggested that agonism increased on days of high female attendance after females had left the lek. Males turned their heads only half as frequently during display as during other activities. These correlative data suggest two mechanisms by which display costs are potentially incurred: 1) a reduction in on-lek foraging time, and 2) reduced visual attention to the surroundings. It is possible that reduced foraging time and reduced vigilance during display may also be costs of increased courtship display in other nonlekking species.