Western Snowy Plovers Charadrius alexandrinus nivosus select nesting substrates that enhance egg crypsis and improve nest survival

Predation is an important cause of nest failure for many birds and has shaped the life-history characteristics of many species, especially ground-nesting shorebirds. We examined nesting success, causes of clutch failure and nest survival in relation to variation in substrate characteristics in a colour-marked population of Western Snowy Plovers Charadrius alexandrinus nivosus breeding on riverine gravel bars in coastal northern California. Plovers experienced higher nesting success on gravel bars than on nearby beaches, which were characterized by more homogeneous, sandy substrates. On gravel bars, Plovers nested in habitats characterized by large, heterogeneous substrates, with more egg-sized stones, compared with random sites. Egg crypsis, as indexed by time required of a naive observer to detect a nest, increased with number of egg-sized substrates. Nest survival correlated negatively with heterogeneity of substrates and positively with the number of egg-sized stones. Consistently high nesting success of Plovers on gravel bars indicates that this high-quality habitat deserves special management considerations given the species' threatened status.