Should I stay or should I go? : geolocators reveal different winter home ranges and -activity patterns in sympatrically breeding razorbills (Alca torda)

Annual migration between breeding- and wintering grounds is a common behavior that is found in a range of taxa, including many seabird-species such as alcids. Within-population-differences in migration strategies, including high or low fidelity in routes, wintering destination and timing, might have a strong impact on survival and later breeding success due to potential differences in e.g. threat exposure and environmental conditions during the inter-breeding season. Knowledge of such is therefore crucial in order to understand the population dynamics of a taxa as well as to improve conservation strategies within environmental management. Through the usage of light based geolocators equipped with saltwater immersion sensors, this study investigated spatial distribution and activity patterns of razorbills breeding in the southern Barents Sea during their non-breeding season of 2018/19. The razorbills were found to divide into at least two main groups depending on their choice of wintering destination. One group migrated south to overwinter in Skagerrak while the other stayed resident in the Barents Sea. The razorbills wintering in the Barents Sea significantly lowered their activity during the main winter-months, spending less time foraging and in flight. The razorbills wintering in Skagerrak did not lower their activity to the same extent, leading to a seasonal difference of time spent foraging and in flight, depending on migration strategy. No difference on body condition between the two groups was found during the following breeding season, suggesting that both strategies might be a viable alternative. However, further research is needed in order to establish an understanding of consistency and drivers of migration in the Barents Sea razorbills as well as any possible long term-fitness consequences