Data from: seasonal patterns and processes of migration in a long-distance migratory bird: energy or time minimization? (Q6685681)

Optimal migration theory prescribes adaptive strategies of energy, time or mortality minimization. To test alternative hypotheses of energy and time minimization migration we used multisensory data loggers recording time-resolved flight activity and light for positioning by geolocation in a long-distance migratory shorebird, little ringed plover Charadrius dubius. We could reject the hypothesis of energy minimization based on a relationship between stopover duration and subsequent flight time as predicted for a time minimizer. We found seasonally diverging slopes between stopover and flight durations in relation to the progress (time) of migration, which follows for a time minimizing policy if resource gradients increase and decrease, respectively. Total flight duration did not differ significantly between autumn and spring migration, although spring migration was 6% shorter. Overall duration of autumn migration was longer than that in spring, mainly due to a mid-migration stop in most birds, when they likely initiated moult. Overall migration speed was not significantly different between autumn and spring. Migratory flights often occurred as runs of 2-7 nocturnal flights on adjacent days, which may be countering a time minimization strategy. Other factors may influence a preference for nocturnal migration, such as avoiding flight in turbulent conditions, heat stress, and diurnal predators.