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

Abstract

Many studies addressing the use of nest materials by animals have focused on only one factor to explain its function. However, the consideration of more than one factor could explain the apparently maladaptive choice of nest materials that makes the nests conspicuous to predators. Here, we tested experimentally whether there is a trade-off in the use of nest materials between the risks of egg predation and overheating when the eggs are not attended by adults in the ground-nesting Kentish plover, Charadrius alexandrinus. For this, we added into nests materials differing in their thermal properties and coloration, thus affecting rates of egg heating and camouflage. Before manipulations, adults had selected light materials that matched worse egg coloration than the microhabitat, likely to buffer the risk of egg overheating. However, the adults did not keep the lightest experimental materials, probably because camouflage worsened. In all nests, adults removed most of the experimental materials independently of their properties, so that egg camouflage returned to the original values within a week of the experimental treatments. Although the thermal environment may affect the choice of nest materials by the plovers, at our study sites it was not likely too stressful as to determine the acceptance of the lightest experimental materials.