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.

Habitat selection determines an animal’s spatial distribution at various scales. In ground breeding birds, selecting the right nesting location can be decisive for the survival of parents and offspring. However, it remains often unclear what cues birds use to settle in their breeding habitat. Ruffs (Calidris pugnax) are waders with highly divergent sex roles: males aggregate for competitive display to attract females (reeves), who then care for the nest and offspring alone. Ruffs frequently breed in coastal wetlands of higher latitudes where they often face the threat of nest loss because of flooding or predation. We investigated which environmental and social cues relate to Ruff nest distributions in a coastal meadow habitat. Using nest locations from five breeding seasons, and their relative distance to other nests, leks, the shoreline and meadow edge, we tested whether Ruff nests are randomly distributed across the suitable breeding habitat or show some level of spatial association. We first compared Average Nearest Neighbour (ANN) distances between Ruff nests (observed and simulated) and spatial features in univariate models. Then, we examined the effect of all spatial features on nest location in a multivariate Generalized Linear Mixed Model (GLMM) using a Bayesian framework. Our results show that nest distribution is non-random; nests are found closer to leks and other nests than expected by chance. In some years, we found nests further away from the meadow edges and shore than expected by chance. Overall, our results suggest that nesting females may use social cues and the distance to habitat boundaries when choosing a nest site. We suggest that understanding the social and environmental factors affecting female nest choice can help to improve the management and conservation routines at the breeding sites of these threatened waders. Our results indicate that lekking sites may be used to identify nesting areas of conservation management value.