Corvids and humans create ecological traps in otherwise suitable Snowy Plover habitat

Conservation relies on knowledge of factors that influence the distribution and abundance of species, with the objective of managing these limiting factors. The Pacific coast population of the Snowy Plover Charadrius nivosus nivosus is listed as threatened, owing to loss and degradation of habitat, predation, and human disturbance. We studied a color-marked population for 18 years along ~100 km of ocean-fronting beach and riverine gravel bar in coastal northern California, USA to examine the influence of food and extent of suitable breeding habitat, as well as the activity of predators and humans on the occurrence and reproductive success of plovers. Plovers occurred in a patchy distribution with many locations unoccupied in most years; less than 10% of cells hosted breeding plovers >90% of the 18 years. Open, expansive habitats, as gauged by width of beach or riverine gravel bar, best explained breeding locations. Within occupied habitats, average fledging success of males varied greatly (0–3 chicks annually), which correlated negatively with activity of Common Ravens Corvus corax and humans, and positively with food. Our results indicate that, although restoration may enhance habitats (i.e., create wider beaches with sparse native vegetation) that attract breeding plovers, a critical vital rate (productivity) for recovery of the listed population is compromised by corvid and human activity; we argue for increased management of these limiting factors.