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Like many seabirds, auks spend most of the year in offshore areas. Information on which oceanic areas they rely on throughout the winter is therefore important in understanding their population dynamics and establishing appropriate conservation measures. The breeding populations of Thick-billed Murres (Uria lomvia), Common Murres (Uria aalge) and Razorbills (Alca torda) in Iceland have been reported declining for the last 30 years. Thick-billed Murres have shown the most alarming rate of decrease, while Razorbills have declined the least. To help understand these changes, we collected information about the non-breeding distribution of these three species by using light-based geolocation. Geolocators were deployed on breeding adults in three different colonies in Iceland in 2013 and 2014. Data showed that the three species’ wintering areas differed substantially. Thick-billed Murres wintered off the west coast of Greenland and East Greenland/Northern Iceland, Common Murres favoured areas around Iceland/East Greenland and to the southwest along the Mid-Atlantic Ridge, and Razorbills were mostly distributed around Iceland. Although some intraspecific variation was evident, we conclude that the population development of Thick-billed Murres in Iceland is likely to be largely influenced by environmental conditions in west Greenland, while Common Murres and Razorbills are more dependent on the oceanic area around Iceland. The results may therefore prove to be an important platform for understanding the population dynamics of these three species in Iceland and informing conservation actions. [ABSTRACT FROM AUTHOR]

Ritenbenk/Innaq in Disko Bay is the only remaining Thick-billed Murre colony in central West Greenland. It has declined by 72% since 1980 and now (2012) holds c.1,100 breeding pairs. In 2005–2006 and 2011–2012, a number of studies were carried out in this colony to improve our understanding of the population decline and its causes. Hunting has previously been identified as a problem for the colony, but local breeding conditions have never been studied and the non-breeding distribution was known only from ringing. Our studies showed that breeding success was moderate to good in the Ritenbenk colony and apparently not limited by food availability. The impact of gull predation was more uncertain, but seemed limited in our study plot. In contrast, estimates of maximum sustainable harvest levels showed that hunting, including illegal activities, was and still is too high and probably can explain much of the population decline. It is puzzling though, that the steepest population decline was observed within the most recent decade when the harvest level was markedly reduced. This may indicate that something else besides hunting mortality affects the colony. The winter distribution of the Ritenbenk birds includes areas in the central North Atlantic, such as the waters around South Greenland, where conditions have been identified as potentially deteriorating due to pronounced oceanographic changes. The potential impact on the Ritenbenk colony, as well as other colonies in the North Atlantic, needs to be studied further. [ABSTRACT FROM PUBLISHER]

When species competing for the same resources coexist, some segregation in the way they utilize those resources is expected. However, little is known about how closely related sympatric breeding species segregate outside the breeding season. We investigated the annual segregation of three closely related seabirds (razorbill Alca torda, common guillemot Uria aalge and Brünnich’s guillemot U. lomvia) breeding at the same colony in Southwest Greenland. By combining GPS and geolocation (GLS) tracking with dive depth and stable isotope analyses, we compared spatial and dietary resource partitioning. During the breeding season, we found the three species to segregate in diet and/or dive depth, but less in foraging area. During both the post-breeding and pre-breeding periods, the three species had an increased overlap in diet, but were dispersed over a larger spatial scale. Dive depths were similar across the annual cycle, suggesting morphological adaptations fixed by evolution. Prey choice, on the other hand, seemed much more flexible and therefore more likely to be affected by the immediate presence of potential competitors. [ABSTRACT FROM AUTHOR]