Nocturnal roost on South Carolina coast supports nearly half of Atlantic coast population of Hudsonian Whimbrel Numenius hudsonicus during northward migration

Hudsonian Whimbrel Numenius hudsonicus are rapidly declining and understanding their use of migratory staging sites is a top research priority. Nocturnal roosts are an essential, yet often overlooked component of staging sites due to their apparent rarity, inaccessibility, and inconspicuousness. The coast of Georgia and South Carolina is one of two known important staging areas for Atlantic coast Whimbrel during spring migration. Within this critical staging area, we discovered the largest known Whimbrel nocturnal roost in the Western Hemisphere at Deveaux Bank, South Carolina. Surveys in 2019 and 2020 during peak spring migration revealed that Deveaux Bank supports at least 19,485 roosting Whimbrel, which represents approximately 49% of the estimated eastern population of Whimbrel and 24% of the entire North American population. The high concentrations of Whimbrel at Deveaux Bank may allow nocturnal roost counts to efficiently track population trends and add greater accuracy to current population estimates. We found that dates within two days of the full moon, when civil twilight and high tide are 30–60 minutes apart, enable more complete and accurate counts. We thus recommend joint consideration of tide and lunar phase for future surveys. The discovery of Deveaux Bank has conservation implications throughout the flyway and presents a unique opportunity to improve our understanding of the role nocturnal roost sites play in the staging ecology of Whimbrel.