Nest survival and failure in ruffs breeding on grazed coastal meadows

Nest survival is a key determinant of birds’ breeding success, particularly in ground-breeding birds, where nest predation is the major cause of reproductive failure leading to demographic decline. Birds can maximize their nesting success by optimising aspects of the socio-spatial environment of a nest, for example by reducing the risk of predation or flooding. Previous research showed that ruff ( Calidris pugnax ) females nest closer to leks and to nests of conspecifics, and in some years, further from the shoreline and from the meadow edge than expected by chance. However, it remained uncertain whether and how social and environmental factors affect nest survival. To fill this gap in knowledge, we analysed daily nest survival in a breeding population of ruffs, using nest locations from six breeding seasons. Following a Bayesian approach, we estimated daily nest survival rates to assess the impacts of social, spatial, and temporal factors on ruff nest survival in three models focusing on distinct sources of mortality: i) all sources of mortality ( Overall model), ii) all sources of mortality except for predation ( No-predation model), and iii) only predation ( Predation model). We also studied the effect of human intervention in clutch incubation as a way to protect nests at increased risk of failure. Overall, younger nests and those at intermediate distances to other nests had the highest daily nest survival, while laying date and distance to paths had a negative effect on daily nest survival only in absence of predation. The use of dummy eggs and artificial incubation of clutches reduced nest mortality of protected nests at strong risk of failure from flooding and cattle trampling, and also reduced the impact of predation. We highlight the need for comprehensive studies about the sources of nest mortality to understand factors affecting population decline of endangered waders and to improve their population recovery through informed species and habitat management.