Population specific annual cycles and migration strategies in a leap-frog migrant

A common migratory pattern in birds is that northerly breeding populations
migrate to more southerly non-breeding sites compared to southerly: a
pattern called leap-frog migration. Not only do populations experience
differences in migration distances, but also different environmental
conditions, which may vary spatiotemporally within their annual cycles,
crating distinctive selective pressures and migratory behaviors.
Information on how populations schedule their annual cycles according to
environmental conditions and by extension, adapt their migratory behaviors
is important to understand drivers of migration and evolution of migration
patterns at large. Here we use light level geolocators and citizen science
data on regional spring arrivals to compare two populations of common
ringed plover Charadrius hiaticula – a textbook example of a leap-frog
migrant – breeding at different latitudes. We 1) describe and characterize
the spatiotemporal patterns of the annual cycles, and 2) test predictions
regarding speed and timing of migration derived from the population
specific characterizations of the annual cycles. Winter distributions
followed a leap-frog migration pattern, i.e. northern breeding population
(NBP) wintered in W Africa and the southern (SBP) mainly in W Europe. The
annual cycles were shifted temporally so that the NBP was always later in
all stages compared to the SBP. The SBP spent more than twice as long time
in the breeding area, but there was no difference in winter residency.
There was no difference in migration duration, nor migration speed,
between the two seasons within population, but the NBP spent more time on
migration in both seasons and migrated faster in spring compared to the
SBP. We also found a larger variation in spring arrival times across years
in the SBP. This suggests that a complex interaction of population
specific timing and variation of breeding onset, length of breeding season
and proximity to the breeding area shape the annual cycle and migratory
behaviors.