Nests, threats and leks: non-random distribution of nests in ruffs ( Calidris pugnax )

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. Ruffs ( Calidris pugnax ) are waders with highly divergent sex roles that frequently breed in coastal wetlands of higher latitudes where they often face the threat of flooding and predation. Males aggregate for competitive display to attract females (reeves), who then care for the nest and offspring alone. We investigated which environmental and social cues relate to nest distributions in this threatened wader species. Using nest and lek locations from five breeding seasons we tested whether Ruff nests are randomly distributed across suitable breeding habitat or show some level of aggregation. We then assessed whether leks and nests are spatially associated, i.e., nests are closer located to leks than expected by chance. Finally, we examined whether reeves consider distance to shoreline and meadow edges, two habitat features that are linked to threats such as flooding and predation, for the choice of their nest location. Our results show that nest distribution is non-random, and nests are found closer to leks and other nests than expected by chance. We found nests further away from the meadow edges and shores than expected by chance suggesting that nesting females try to minimize the risk of predation and flooding. 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 can be used to recognise areas of conservation and management value.