Ecology and evolution of large-scale bird migration patterns : A natural history and comparative study of the migration in common and little ringed plovers

Abstract: Migration distance and seasonal redistribution patterns may vary between and within bird populations. A common pattern is leap-frog migration, in which northerly breeding populations migrate farther and winter south of more southerly breeding populations. Another common pattern is difference in migration distances between males and females within the same population. Evidently different populations and sexes may experience different environmental conditions and selection pressures throughout the annual cycle. Such systems are interesting from an evolutionary perspective, since it allows researchers to identify and study cost-benefit trade-offs, ecological drivers and constraints to better understand species distributions and behavioral adaptations, such as migration. The aim of this thesis was to study the migration patterns and processes in the common ringed plover Charadrius hiaticula and little ringed plover Charadrius dubius to test predictions and assumptions in the underpinning hypotheses regarding the evolution of between and within population migration patterns, and behavioral adaptations associated with the migratory journey. By studying different populations of common ringed plovers, a textbook example of leap-frog migration, the general leap-frog pattern was confirmed. However, two populations breeding on the same sub-Arctic latitude separated in the winter. Relative winter distribution, body size patterns and autumn departure/arrival patterns between four populations suggest that neither body size nor spring predictability could explain leap-frog migration. Thus, two hypotheses explaining leap-frog migration could be rejected. Individuals from a temperate population spread out over the whole known (subspecies-specific) wintering distribution area. Interestingly, on average, males were found to migrate farther (~ 800 km) compared to females. This pattern is rare among birds. Neither of the proposed hypotheses set out to explain differential migration could satisfactorily explain the observed pattern. A new hypothesis was formulated (but not tested), which proposes that sex specific energetic needs upon spring arrival and winter site-specific fueling rates may sometimes benefit one sex - in this case males - to migrate farther.Migration distance alone did not seem to have an effect on migration speed in the common and little ringed plover. Contrary to the general predictions and observations, lower migration speeds were found in spring compared to autumn in little ringed plovers and in a temperate breeding population of common ringed plover. Interestingly, the Arctic population of common ringed plovers realized a higher spring migration speed compared to the temperate population, suggesting that high fueling rates may be attained on European spring stopover sites, well timed in relation to the onset of the northern breeding season. Temperate populations of common ringed plovers arrive in spring with a higher inter-annual variation compared to Arctic populations, indicating a more flexible migratory schedule. Migration distance and season influenced the number, organization and duration of migratory flights in the common ringed plover. In autumn, there was no difference in number of migratory flights between individuals migrating different distances. However, individuals migrating longer distances initially made 2-4 short flights followed by a longer flight. This is indicative of a time minimizing strategy, which was unexpected given previous assumptions of autumn migration being more relaxed. In spring however, the number of flights increased with distance and there is no clear way to distinguish between strategies without knowledge of fueling conditions.