Boldness and Stress Responsiveness as Drivers of Nest-Site Selection in a Ground-Nesting Bird

Nest-site selection involves trade-offs between the probability of nest discovery by egg predators, danger to the incubating parent from predators and provision of an appropriate microclimate for incubation, and all three components are potentially influenced by nest concealment and distance to habitat edge. Personality traits also affect habitat choice, and the trade-off hypothesis suggests that variable stress-coping strategies may evolve because individuals prioritize either productivity (proactive coping) or survival (reactive coping), both of which cannot be simultaneously maximized. Applying this hypothesis to understand nest-site selection by female eider ducks (Somateria mollissima), we predicted that bold individuals with attenuated stress responsiveness should select concealed nests further away from the shore, thereby promoting clutch survival at the potential expense of reduced escape opportunities for themselves. In testing this prediction, we controlled for individual quality (female body condition and breeding experience) and verified that individual stress responses and nest-site preferences were consistent by analysing their repeatability. Finally, we analysed how the viable proportion of the clutch was related to nest-site and female characteristics. Our prediction was supported: bold females [short flight initiation distance (FID)] and those with lower handling-induced body temperature were found in concealed nests, and bold females and those with lower handling-induced corticosterone concentrations occupied nests farther from the shore. The viable proportion of the clutch peaked at intermediate proportional nest-cover and increased linearly with increasing nest distance from the shore. Stress coping styles may thus be related to nest-site selection, but their fitness consequences may be manifested indirectly through the nest-site characteristics.