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

Abstract

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. Perhaps to avoid these negative possibilities, some birds cover their eggs with materials when they 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 simultaneously maintain the eggs' camouflage. There was a negative relationship between nest attendance and ambient temperature, but only during mid-morning, the period of the day when eggcovering was most frequent. Indeed, during mid-morning egg-covering not only served to better camouflage the eggs, but also to maintain egg temperatures within optimal thermal thresholds for embryogenesis while the nests remained unattended. During other periods of the day, covered eggs in unattended nests overheated (e.g., afternoon) or did not reach the optimal temperature for embryogenesis (e.g., early morning). During periods in which eggs may be uncovered to alleviate overheating, unattended nests may be easier to locate by predators, because the eggs are less well camouflaged. Therefore, camouflage and appropriate thermal environment are inseparable functions of egg-covering in the ground-nesting Kentish plover.

Does the use of nest materials in a ground-nesting bird result from a compromise between the risk of egg overheating and camouflage?

“…The importance of the materials in improving camouflage may be especially significant when the match between the nesting habitats and the eggs is poor. In such cases, the birds may improve egg camouflage with the materials that they add to nests (Amat et al, 2012; Troscianko et al, 2016a). This in turn shows that some birds are selective in their choice of nesting materials (Kull, 1977; Solís and de Lope, 1995; Gómez et al, 2018a).…”

The impact of social structure on breeding strategies in an island bird

“…Our results instead suggest that a combination of individual habitat preferences or site fidelity may predict the structure of breeding territories. Habitat preferences may be linked to local variation in ambient temperatures, predator densities, as well as the availability of different nest substrates or nest cover, which can have strong implications for the success of nesting attempts in Kentish plover via heat stress to eggs and predation risk 47 , 68 – 71 . In addition, we found no evidence that the number of breeding pairs within 100 m of a focal bird’s nest, influenced their nesting success.…”

No Evidence of Deliberate Egg Soiling in the Pied Avocet Recurvirostra avosetta to Improve Camouflage

“…Such behaviours include nest distraction displays (Gochfeld, 1984; Gómez-Serrano & López-López, 2017), or even varying flushing distances by incubating adults depending on the degree of nest camouflage (Wilson-Aggarwal et al ., 2016; Amat et al ., 2017). Moreover, shorebirds may intentionally modify the visual appearance of nest sites by adding materials that render the eggs/nests harder to find visually (Solís & de Lope, 1995; Gómez et al ., 2018), and may even use these materials to cover the eggs during parental absences from the nest, resulting in even better camouflage (Summers & Hockey, 1981; Amat et al ., 2012; Troscianko et al ., 2016a).…”

“…flage (Summers & Hockey, 1981;Amat et al, 2012;Troscianko et al, 2016a). Mayani-Parás et al (2015) reported another possible behaviour used by ground-nesting birds to improve egg camouflage.…”