Long-term monitoring reveals population growth and management implications for Anarhynchus nivosus nivosus (Western Snowy Plover) at two San Francisco Bay Area national parks

Abstract

Since the Pacific Coast population of Anarhynchus nivosus nivosus (Western Snowy Plover) was federally listed as threatened in 1993 under the U.S. Endangered Species Act, land managers and biologists throughout the species’ range have implemented various management strategies aimed at mitigating threats. Here we examine long-term trends (1995–2022) at Point Reyes National Seashore, California and show that the breeding population has undergone periods of growth and decline, though overall the population has increased significantly since the time of its listing, when management efforts were first implemented at this location. This local population growth has been concurrent with overall population growth at larger geographic scales within the species’ range. Additionally, we show that A. n. nivosus nonbreeding populations have increased significantly at Point Reyes (2004–2022) and at 2 sites located in nearby Golden Gate National Recreation Area (1994–2022). These results suggest that recovery efforts have resulted in a growing local breeding and nonbreeding A. n. nivosus population in this region and substantial progress towards achieving recovery goals. Although we were not able to measure the relative impact of individual management practices (e.g. fencing, beach closures, and habitat restoration), nest-predator exclosures have had a significant impact on improving nesting success. More research is needed, however, to understand how to balance increased nest success with potential abandonment and/or adult mortality that can result from the use of exclosures. Additionally, results indicate that nest predation by Corvus corax (Common Raven) is the single most important factor limiting nesting success at the Point Reyes site, underscoring the need for a targeted predator management program at this and other important A. n. nivosus sites.