| Conservation relies on accurate knowledge of factors that influence the distribution and abundance of species, with the objective of managing these limiting factors. The western snowy plover (Charadrius nivosus nivosus) is listed as threatened under the federal Endangered Species Act owing to habitat loss and degradation, predation, and human disturbance. We studied a color-marked population for 17 years along ~100 kilometers of ocean-fronting beach and riverine habitat in northern California to examine the influence of food and extent of breeding habitat, as well as the activity of predators and humans on the occurrence and reproductive success of plovers. Plovers were patchily distributed within suitable habitat. The presence of breeding plovers was best explained by width of beach or gravel bar, which is a surrogate for the open, sparsely vegetated habitats that plovers favor for breeding. Across occupied habitats, average per capita fledging success of males varied greatly (0-3), and was inversely correlated with activity of common ravens (Corvus corax) and humans. Our results indicate that although restoration may enhance habitats that attract breeding plovers, a critical vital rate (productivity) essential for population growth is compromised by corvid and human activity. We argue for additional efforts to manage these limiting factors. |