Migration patterns in two populations of the Common Ringed Plover Charadrius hiaticula, examined with light levelgeolocators

Abstract: Leap-frog migration, i.e. when a northerly breeding population/species migrates further south compare to southerly breeding population/species, is a common migration pattern in birds. However, it is still unknown which factors facilitate the evolution of such a migration pattern pattern. A textbook example of a species exhibiting leap-frog migration is the Common Ringed Plover Charadrius hiaticula hiaticula. However, it has been debated weather the pattern is as clear as initially described. In this study, I use light level geolocators to evaluate the geographical segregation during winter for two populations of Common Ringed Plover (breeding in northern and southern Sweden, respectively), as well as describe and compare migration strategies and annual time budgets to better understand the evolution of leap-frog migration. Here I present tracks from 4 individuals breeding in Abisko (N Sweden) and 9 breeding in Ottenby (S Sweden). Average wintering positions for birds breeding in Ottenby corresponded to NW Iberian Peninsula, while it was situated in W Mali for the birds breeding in Abisko. Measured in N-S direction, the spatial segregation during winter was thus 2999 km. Autumn migration was commencing on average July 30 and Aug 10, from Ottenby and Abisko, respectively. Only 2 individuals migrating from Ottenby had longer stopovers in Europe, but total duration of migration was on average 7.8 d. This suggests that birds breeding at Ottenby are using an energy minimization strategy because the distance could easily be covered within 2 d. Arrivals at the wintering grounds were on average Aug 7 and Sep 25, and thus birds from Ottenby had prior occupancy at the Iberian sites. Departure from the wintering ground was on average March 2 and May 3, respectively. Birds arrived to their breeding grounds on average March 8 and May 31, respectively. There was no large difference in duration of the stay at the wintering grounds between the two populations. However, there was a twofold difference in time spent at the breeding grounds, where birds breeding in Ottenby spent on average 40% of the total time budget there, whereas the Abisko birds only spent 20% on the breeding grounds. Prior occupancy at wintering sites observed in this study is in agreement with several hypotheses regarding leap-frog migration. One hypotheses regarding dominance by body size can be rejected. However, I cannot based on these data conclude if there is actually competition between birds of the two population at the northerly wintering grounds in Iberia. Early arrival to the breeding grounds for birds breeding in Ottenby, as well as late departure, suggests that the relative importance of the breeding grounds is high in this population. In addition, the large proportion of time spent on the breeding ground in the southern population is in agreement with the time allocation hypothesis. However, neither of the hypotheses can at present be rejected until further data regarding winter survival, reproductive success and cost of migration is available.