Impacts of wind on individual migration schedules of New Zealand bar-tailed godwits

Despite clear links between wind conditions and timing of migration at the population level, no study has examined the contribution of winds to annual variation in the migration timing of individual birds. At a single nonbreeding site in New Zealand, we closely monitored 3 years of departures of bar-tailed godwits (Limosa lapponica baueri), long-distance migrants with remarkable annual consistency in individual migration schedules. Although individual godwits showed very little variation in departure date and generally experienced favorable departure conditions, most off-schedule departures were explained by maximizing initial wind assistance for the nonstop flight to Asia. Surprisingly, early departures attributable to wind were more common and of greater magnitude than wind-related departure delays, and prolonged weather-related departure lulls did not always result in late-departing individuals. Thus, our results show that knowledge of individual departure decisions with regard to wind can strongly influence interpretation of population patterns. Early departures associated with winds, previously only demonstrated theoretically, may reflect conservative timing and extent of premigratory fueling, a possible adaptation for extreme long-distance migration in variable conditions.