Consequences of migratory distance, habitat distribution and season on the migratory process in a short distance migratory shorebird population

The migratory process in birds consists of alternating periods of flight and fueling. Individuals of some populations make few flights and longer stopovers, while others make multiple flights and shorter stopovers. Shorebirds are known for executing marathon flights, but most populations studied are long distance migrants, often crossing major barriers and thus forced to make long non-stop flights. The sub-division of migration in short/medium distance migratory populations, where the total migration distance is shorter than documented non-stop flight capacity and routes offer more homogenous stopover landscape, is little explored. Here we combine data based on conventional light level geolocators and miniaturized multi sensor loggers, comprising acceleration and light sensors, to characterize the migratory routes and process for a short/medium distance (~1300-3000 km) migratory population of common ringed plover (Charadrius hiaticula) breeding in southern Sweden. We were specifically interested in the variation in number and duration (total and individual) of flights/stopovers between seasons and in relation to migration distance. Most stopovers were located along the European Atlantic coast. On average 4.5 flights were made during autumn migration irrespective of migration distance, but in spring the number of flights increased with distance. The equal number of flights in autumn was explained by that most individuals migrating farther performed one longer flight (all but one lasting >20 hours), likely including crossing of the Bay of Biscay. Median flight duration was 8.7 and 5.5 hours in autumn and spring, respectively, and median stopover duration was ~1 day. Total flight duration was 36% lower in spring compared to autumn and there was a positive relationship with migration distance.Our results suggest that when suitable stopover sites are present common ringed plovers prefer making shorter flights even if longer flights are possible. This behaviour is predicted under both time and energy minimizing strategy, although the variable flight distances suggest a policy of time selected migration. Even if populations using several stopover sites seem to be more resilient for environmental change along the route, these results are informative for conservation efforts and for predicting responses to future climate change.

Methods
Light level geolocators and multi sensor data loggers.