Dual function of egg-covering in the Kentish plover Charadrius alexandrinus

摘要

Many bird species take recesses during incubation, and while the nests are unattended, the eggs may both be vulnerable to predation and reach suboptimal temperatures for embryo development.\udPerhaps to avoid these negative possibilities, some birds cover their eggs with materials when\udthey depart from nests. We examined experimentally, using the ground-nesting Kentish plover as model species, whether egg-covering allows egg temperatures to remain within optimal limits for embryogenesis in unattended nests, thus reducing the requirements of contact incubation, and\udsimultaneously maintain the eggs’ camouflage. There was a negative relationship between nest\udattendance and ambient temperature, but only during mid-morning, the period of the day when eggcovering\udwas most frequent. Indeed, during mid-morning egg-covering not only served to better\udcamouflage the eggs, but also to maintain egg temperatures within optimal thermal thresholds for\udembryogenesis while the nests remained unattended. During other periods of the day, covered\udeggs in unattended nests overheated (e.g., afternoon) or did not reach the optimal temperature for\udembryogenesis (e.g., early morning). During periods in which eggs may be uncovered to alleviate\udoverheating, unattended nests may be easier to locate by predators, because the eggs are less\udwell camouflaged. Therefore, camouflage and appropriate thermal environment are inseparable functions of egg-covering in the ground-nesting Kentish plover.