Habitat restoration improves Western Snowy Plover nest survival Katelyn M. Raby* & Mark A. Colwell Wildlife Department, Humboldt State University, 1 Harpst Street, Arcata, CA 95521, USA *Corresponding author: kmr803@humboldt.edu Raby, K.M. & M.A. Colwell. 2020. Habitat restoration improves Western Snowy Plover nest survival. Wader Study 127(2): 130–140. INTRODUCTION Te study and documentation of vital rates of threatened and endangered species is imperative to understanding the factors limiting their population size and growth (Colwell 2010). For avian species, nest survival is ofen used as a measure of productivity, which, in turn, is used in combination with other vital rates (e.g., juvenile and adult survival) to model population growth and viability (Jones & Geupel 2007). Although research suggests adult survival has the greatest infuence on shorebird population growth, productivity is generally the focus of adaptive management eforts to increase shorebird populations because it is difcult to enhance survival of adults (Colwell 2010, Dinsmore et al. 2010, Mullin et al. 2010, Cruz- López et al. 2017). Demographic measures like productivity are also used to indirectly measure habitat quality, such as by quantifying variation in nest survival (Johnson 2007), and can be used by managers to assess the efcacy of management actions. Te U.S. Fish & Wildlife Service listed the Pacifc Coast population of the Western Snowy Plover Charadrius nivosus nivosus (hereafer Snowy Plover) as threatened in 1993 afer a documented decline in both population size and occupied breeding sites (Page & Stenzel 1981, Page et al. 1991). Te recovery plan identifed three main factors limiting the coastal population of Snowy Plovers: the loss and degradation of habitat (owing primarily to invasive plants and urban development), increasing predator populations (resulting in high levels of egg and chick loss), and human disturbance (USFWS 2007). Loss and degradation of Snowy Plover breeding habitat is largely associated with the rapid expansion of the non- native European Beach Grass Ammophila arenaria (USFWS 2007), which creates steep and densely vegetated foredunes and backdunes (Buell et al. 1995) and potentially provides cover for predators (USFWS 2007). Plovers prefer to court and nest in relatively fat, open, sparsely vegetated habitats, which probably enables early detection of predators (Page et al. 2009, Muir & Colwell 2010, Leja 2015). Habitat restoration creates suitable Snowy Plover breeding habitat by using heavy equipment to recontour (fatten) the foredune and by removing invasive plants (Zarnetske et al. 2010). Sometimes oyster shells are spread to increase crypsis, and thus survival, of eggs and chicks by creating a heterogeneous substrate (Colwell et al. 2011). Snowy Plovers preferentially selected restored habitats (84% of nests) in northern California (Leja 2015) and habitat management signifcantly increased nest survival along the Oregon coast (Dinsmore et al. 2014). Predation can account for approximately 80% of nest loss research paper Wader Study 127(2): 130–140. doi:10.18194/ws.00199 Keywords Charadrius nivosus habitat quality productivity conservation predation human disturbance shorebirds waders threatened Productivity measures, such as nest survival rates, are often used to indirectly assess habitat quality and guide management practices for conservation of threatened and endangered species. The Western Snowy Plover Charadrius nivosus nivosus is listed as threatened due to three limiting factors: human disturbance, increasing native and introduced predator populations, and the loss and degra- dation of habitat. We examined the relative infuence of these three limiting factors on nest survival, using 14 years of data (n = 610 nests) at eight sites in Humboldt County, California, USA. Survival varied by year and site, and increased with nest age and as the breeding season progressed. Habitat restoration had the greatest infuence on nest survival. Both natural (tidal overwash) and human- implemented restoration had a positive efect on nest survival, whereas unre- stored areas had a negative efect. Naturally restored areas had a stronger efect (higher and less variable survival estimates) on nest survival than human-restored areas. Human and predator activity were not strong predictors of nest survival. Consequently, we recommend that managers focus on conserving, maintaining, and creating restoration areas to enhance Snowy Plover nest survival.