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

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.