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 a major cause of reproductive failure. Birds can maximise their nesting success by optimising aspects of the sociospatial 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 meadow edges than expected by chance. However, whether and how social and environmental factors affect nest survival remains unclear. 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 effects of an intervention to protect nests at increased risk of failure by replacing their eggs with plastic dummies and artificially incubating the collected clutches. Overall, younger nests and those at intermediate distances to other nests had the highest daily nest survival, whereas laying date and distance to paths had a negative effect on daily nest survival in the No-predation model. The use of dummy eggs reduced nest mortality of protected nests at strong risk of failure from flooding and cattle trampling, as well as the impact of predation. We highlight that identifying the sources of nest mortality is necessary to inform species and habitat management, ameliorate productivity and improve the recovery of endangered wader populations.