Apparent annual survival of adult Whimbrels in the Pacific Americas Flyway

For long-distance migratory species, understanding mortality, and inversely survival, across the annual cycle is crucial for identifying where bottlenecks to population growth occur so that effective conservation actions can be implemented. However, demographic information, including estimates of adult survival, are sparse or lacking for many Western Hemisphere shorebird populations. We therefore conducted a study to estimate the apparent annual survival of adult Whimbrels Numenius phaeopus on Chiloé Island, Chile, a major wintering area (austral summer) in the Pacific Americas Flyway. We studied Whimbrels at four bays on the eastern coastline of the island, where we cannon-netted, color-flagged and resighted Whimbrels during six periods between December and February, 2007–2012. Using resights of adult birds, we estimated apparent survival using Cormack-Jolly-Seber models. From the most plausible model, we estimated a constant apparent survival rate of 0.86 ± 0.01 (SE) for adult Whimbrels wintering on Chiloé Island from 2007 to 2012. Encounter rates varied with resighting effort and ranged from 0.59 ± 0.05 (SE) in years of low effort to 0.83 ± 0.02 in years of high effort. Our estimate of annual survival was higher than that reported for the Whimbrel population using the Atlantic Americas Flyway. Our estimate may serve as a gauge to evaluate the population health of Whimbrels in other flyways across the globe.