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.