Strong migratory connectivity indicates Willets need subspecies-specific conservation strategies

ABSTRACT By combining all available banding and tracking data, we found that Willets (Tringa semipalmata) have a strong migratory connectivity between breeding and nonbreeding locations at the range-wide and subspecies levels, exposing two subspecies to varying threats such as hunting for the eastern subspecies (Tringa semipalmata semipalmata) and climatically-altered coastal habitats for both subspecies. We found that western Willets (Tringa semipalmata inornata) primarily used nonbreeding habitats along the Pacific Coast of the United States, although their reported nonbreeding range extends to the US Atlantic and Gulf Coasts and the Pacific Coast of Central and South America. Eastern Willets wintered in Central and South America, which covers much of the subspecies' known nonbreeding range. By quantifying migratory connectivity within and between two subspecies, we could suggest subspecies-specific threats and potential limiting factors in the breeding and nonbreeding periods of the annual cycle of a declining migratory shorebird. Effective management of the species will likely require a range of conservation strategies across the diverse nonbreeding regions the two subspecies occupy within the United States, Central America, and South America. However, more data are needed from Willets breeding in mid-continental North America to understand the complete extent of overlap of the two subspecies throughout the annual cycle. The strong migratory connectivity documented here highlights the need to manage Willets by subspecies and protect a diversity of breeding and nonbreeding habitats, which will benefit the conservation of other shorebird species that overlap with Willets throughout the annual cycle. LAY SUMMARY The eastern and western subspecies of Willets (Tringa semipalmata) are both declining and have little overlap in breeding and nonbreeding ranges. Tracking and banding data show that Western Willets from Canada and the western United States wintered in California and Central America. Eastern Willets from the Atlantic Coast wintered in northern South America and those from the Gulf Coast wintered on the Pacific Coasts of Central America and Ecuador. Both subspecies are threatened by habitat loss from climate change and development and the eastern subspecies has additional threats from hunting. Strong migratory connectivity estimates between and within subspecies verify that subspecies-specific management actions are needed and indicate that population-specific actions are needed as well. More information is needed on the migration of individuals in the center of the species range and where and when the two subspecies overlap to better understand where the two subspecies are relying on the same habitats and encountering the same threats. RESUMEN Al combinar todos los datos de anillamiento y seguimiento disponibles, descubrimos que Tringa semipalmata tiene una fuerte conectividad migratoria entre los lugares reproductivos y no reproductivos a nivel de todo el rango de distribución y de las subespecies, revelando que dos subespecies están sujetas a diversas amenazas, como la caza para la subespecie T. s. semipalmata y la presencia de hábitats costeros climáticamente alterados para ambas subespecies. Encontramos que T. s. inornata usó principalmente hábitats no reproductivos a lo largo de la costa del Pacífico de los Estados Unidos, aunque su rango no reproductivo reportado se extiende hasta las costas del Atlántico y del Golfo de los EEUU y la costa del Pacífico de América Central y del Sur. T. s. semipalmata invernó en América Central y del Sur, lo que cubre gran parte del rango no reproductivo conocido de la subespecie. Al cuantificar la conectividad migratoria dentro y entre las dos subespecies, podríamos sugerir amenazas específicas para las subespecies y potenciales factores limitantes en los períodos reproductivos y no reproductivos del ciclo anual de un ave playera migratoria en declive. El manejo efectivo de la especie probablemente requerirá una variedad de estrategias de conservación en las diversas regiones no reproductivas que ocupan las dos subespecies dentro de los Estados Unidos, América Central y América del Sur. Sin embargo, se necesitan más datos sobre la reproducción de T. semipalmata en el centro continental de América del Norte para comprender el alcance completo de la superposición de las dos subespecies a lo largo del ciclo anual. La fuerte conectividad migratoria documentada aquí destaca la necesidad de manejar a T. semipalmata por subespecie y de proteger una diversidad de hábitats reproductivos y no reproductivos, lo que beneficiará la conservación de otras especies de aves playeras que se superponen con T. semipalmata a lo largo del ciclo anual.