Demographic Consequences of Off-River Nesting for Piping Plover (\u3ci\u3eCharadrius melodus\u3c/i\u3e) and Interior Least Tern (\u3ci\u3eSternula antillarum athalassos\u3c/i\u3e) in the Lower Platte River System, Nebraska

Abstract

Piping plovers (Charadrius melodus; hereafter, plovers) and interior least terns (Sternula antillarum athalassos; hereafter, terns) are two avian species that nest along the Lower Platte River system (LPRS) in Nebraska. In the LPRS, river sandbars provide natural nesting habitat, but off-river sites provide substantial nesting habitat especially when sandbar habitat is scarce. Although presumed to be important for the persistence of plovers and terns, off-river habitat is not self-sustaining and predicted to decline. Understanding the vital rates of plovers and terns in the LPRS will inform the role of off- river sites in the future conservation and persistence of plovers and terns. I assessed consequences of off-river nesting at sandbars and off-river sites using a long-term database collected by the Tern and Plover Conservation Partnership from 2008–2023. I also investigated other factors that could affect vital rates: nest initiation and hatch date, extreme temperatures, conspecific and heterospecific nesting proximity, and nest exclosure usage (plovers only). For plovers, I evaluated annual and within-seasonal adult survival, annual hatch-year survival, pre-fledging chick survival, and pre-fledging chick growth rates at off-river sites, and nest survival at off-river sites and sandbars. For terns, I evaluated pre-fledging chick growth rates and nest survival at off-river sites and sandbars. I did not find evidence for demographic consequences between off-river sites and sandbars. Demographic consequences among off-river site types varied by vital rate and species. Seasonal date, nest age, proximity to tern nests, nest exclosures, and temperature factors affected vital rates. These results demonstrate the dynamics and importance of off-river sites for plovers and terns in the LPRS. The lack of evidence for demographic consequences of off-river nesting suggests that off-river habitat may support plovers and terns similarly to river sandbars. Continued monitoring and study of plovers and terns at off-river sites and sandbars, particularly in changing climatic and industry conditions, may further support the persistence of these species in the LPRS. Advisor: Mark Vrtisk