Residency, recruitment, and stopover duration of hatch-year Roseate Terns (Sterna dougallii) during the premigratory staging period

Seabird demography and spatial distribution outside of the breeding season are poorly understood, and migratory stopover and staging sites represent important energetic bottlenecks during the avian annual cycle. We quantified hatch-year Roseate Tern (Sterna dougallii) weekly residency, weekly recruitment rate into the staging population, and derived weekly staging population growth rate during two postbreeding, premigratory staging seasons (2014 and 2015) at Cape Cod National Seashore, Massachusetts, USA. We also estimated hatch-year tern stopover duration at Cape Cod staging grounds. Tern residency probability at Cape Cod National Seashore during 2014 and 2015 was nearly 1 during the first weeks of the season and decreased steadily over the last 4 weeks to ~0.5 in the final week of the study. Recruitment rates into the staging population, representing the weekly per capita change in hatch-year terns present during the staging season, indicated that most terns arrived on the staging grounds during the first weeks of the staging season (16 July to 19 August). We also identified differences in staging duration between birds from the two breeding regions. Hatch-year terns from the southernmost region spent less time staging at Cape Cod National Seashore than their northern counterparts in both 2014 and 2015. These differences may indicate alternative staging strategies for individuals originating in different regions and possibly reveal differences in resource conditions between these areas, for example, in the availability of ephemeral prey fish.