Winter population trends and environmental drivers for three species of temperate shorebirds

Current assessments indicate that populations of several species of North American shorebirds are declining rapidly. However, limited monitoring programs south of the U.S.-Mexico border have precluded assessments of the conservation status of temperate breeders on their principal wintering grounds. The Migratory Shorebird Project (MSP), active since 2011 throughout the Pacific Americas Flyway, provides an opportunity to detect changes in non-breeding shorebird distribution and abundance. We used annual survey data collected using the MSP monitoring protocol to assess population trends of three temperate breeders: Marbled Godwit (Limosa fedoa), Willet (Tringa semipalmata), and Long-billed Curlew (Numeniues americanus) on their main wintering grounds in northwest Mexico and California. We also analyzed the associations be-tween fluctuations in their abundance and environmental variables using Generalized Linear Mixed Models. We found a significant negative trend in the wintering population of Marbled Godwit and Willet in California and the Baja California Peninsula (BCP). The BCP was the most important region for these three species in the study area, followed by Sonora, Sinaloa, Nayarit (SSN), and California. In addition, we determined that Marbled Godwit abundance was negatively associated with precipitation and positively associated with minimum temperature from January. Willet abundance also was positively associated with minimum temperature, but negatively with sea surface temperature and precipitation. Association of Long-billed Curlew abundance with precipitation was positive and significant. Our study provides evidence that temperate shorebirds are declining and their fluctuations are associated to environmental variables, and highlights the importance of long-term winter shorebird surveys for understanding drivers of populations change that can then be used to identify management and adaptation strategies.