Age, season, and sex modify the use of external migratory cues by American Woodcock (Scolopax minor)

R Code and Data to accompany manuscript "Age, season, and sex modify the use of external migratory cues by American Woodcock (Scolopax minor)". Abstract: Timing of migration is seasonal and tied to changing photoperiod; however, individual birds rely extensively on external environmental cues, such as weather, to assess likely flight conditions and make fine-scale decisions about migratory departures. Considerable variation may exist among individuals in how they respond to specific cues, in turn producing intraspecific variability in aspects of migration timing and flight distances. We were interested in how external environmental cues (e.g., weather, lunar cycles) were associated with departure decisions in American Woodcock (Scolopax minor), and whether there was consistent variation in these decisions among individuals based on their age and sex. Between 2017-2020, we captured and attached satellite transmitters to 304 American Woodcock throughout eastern North America and obtained location data as they migrated between summering and wintering areas during both autumn and spring. We used conditional logistic regression and general linear models in a case-control study design, which allowed us to evaluate individual American Woodcock selection for potential cues at departure. We further explored how individual use of specific wind conditions influenced the distance covered during migratory flights. American Woodcock responded to barometric pressure, moon illumination, temperature, presence of tailwinds, and wind speed when making departure decisions, but selection varied by season, age, and sex. In woodcock responded to tailwind assistance, and departed under lower temperatures and barometric pressure, however, young birds making their first migration were more responsive to temperature and less responsive to wind assistance than adult birds. During spring migration, female American Woodcock showed a greater selection for wind assistance and higher barometric pressure, whereas males showed stronger response to warmer temperatures and greater moon illumination. American Woodcock that departed using tailwinds generally had longer flight distances, which we assume reflected more efficient flight associated with wind assistance. Adults were able to better capitalize on more favorable flight conditions during autumn migration, whereas decision-making during spring migration was instead driven by sex-specific motivations that were likely associated with breeding.