Repeatability and Flexibility in the Migration Strategies of an Arctic Seabird
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- Institutt for biologi 
The strategy of migration has evolved independently in many animal groups, but it is most widely and well developed in birds. Migrating species are expected to be severely affected by human induces climate change, and the effects of climate change is already seen in the phenology of migrating birds, with trends for changes in spring arrival and breeding dates. The effects of climate change are particularly pronounced in the Arctic. Seabirds represent an essential component of the Arctic marine ecosystem, and are amongst the most threatened organisms on Earth. It has been suggested that spatial and temporal flexibility is advantageous in a rapidly changing climate. Little is known about the individual flexibility of migration and wintering strategies of seabirds breeding in Svalbard. In this study light-level geolocators have been used track the migration of females of an Arctic population of common eiders Somateria mollissima breeding in Kongsfjorden, Svalbard over several years (2-6). I looked at the consistency in winter area and the repeatability in the timing of migration in this population, and the individual flexibility in winter area and timing of migration. I also investigated which factors affect the timing of migration. The eiders in this breeding population winter in two distinct areas, Iceland and northern Norway, and only one of the individuals tracked switched between the two wintering areas. This consistency in the winter area may affect the eiders adversely if the conditions in their winter area are changing for the worse. There was a wide range of timing of migration and a relatively high repeatability in the timing of both spring and fall migration. There was some degree of individual temporal flexibility in migration, but I found no effect of year in the timing of migration. For flexibility to be beneficial it should respond to specific cues to allow behavioral changes to track the best timing. It therefore remains unclear whether or not the flexibility I observed will help this population buffer possible changes in the climate. Repeatability can be interpreted as an upper estimate for heritability, so the high repeatability and the wide range of timing of migration may indicate that if there is selection for individuals arriving earlier to the breeding ground, the eiders could perhaps adapt to earlier springs through natural selection.