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Southwest Greenland constitutes an internationally important wintering area for seabirds, including Thick-billed Murres (Uria lomvia (Linnaeus, 1758)), but their prey may be affected by the general warming of this sub-Arctic region. We compared murre diet collected in winter in the 1990s and in the 2010s around Nuuk, Greenland. Fish made up 36% of the diet (wet mass) and crustaceans 63% in the 1990s, changing to 22% and 78% in the 2010s, respectively. Capelin (Mallotus villosus (Muller, 1776)) was the dominant fish species, and the smaller contribution in the 2010s coincided with declining densities of capelin around Nuuk. The crustaceans were dominated by two krill species (Meganyctiphanes norvegica (M. Sars, 1857) and Thysanoessa inermis (Kroyer, 1846)). However, M. norvegica was only important in the 2010s (51% wet mass), while T. inermis was dominating the 1990s with 62% wet mass and only 23% in the 2010s. The dominance of M. norvegica in the 2010s confirmed our expectations of a gradual 'borealization' of this region due to the generally warming sub-Arctic. The smaller contribution of fish in the diet may also support the hypothesis of deteriorating winter conditions for murres. Apart from the diet, plastic was found in 15% of the birds and 53% had parasitic nematodes. Key words: seabird winter diet, Thick-billed Murre, Uria lomvia, southwest Greenland, borealization, krill, capelin, Mallotus villosus. Si le sud-ouest du Groenland constitue une aire d'hivernage d'importance internationale pour les oiseaux marins, incluant le guillemot de Brunnich (Uria lomvia (Linnaeus, 1758)), le rechauffement general de cette region subarctique pourrait avoir une incidence sur leurs proies. Nous comparons les regimes alimentaires hivernaux de guillemots durant les annees 1990 et 2010 dans les environs de Nuuk (Groenland). Les poissons constituaient 36 % (masse humide) de leur alimentation et les crustaces, 63 %, dans les annees 1990, ces proportions passant a 22 % et 78 %, respectivement, durant les annees 2010. Le capelan (Mallotus villosus (Muller, 1776)) etait l'espece de poisson dominante, et le plus faible pourcentage de poissons dans les annees 2010 coincide avec des densites de capelans reduites aux environs de Nuuk. Parmi les crustaces consommes, deux especes de krill (Meganyctiphanes norvegica (M. Sars, 1857) et Thysanoessa inermis (Kroyer, 1846)) dominaient. Toutefois, M. norvegica n'etait important que dans les annees 2010 (51 % masse humide), alors que T. inermis etait dominant dans les annees 1990 (62 % masse humide, contre seulement 23 % durant les annees 2010). La predominance de M. norvegica dans les annees 2010 confirme nos predictions d'une <> progressive de cette region decoulant du rechauffement general de la region subarctique. La diminution de la proportion des poissons dans l'alimentation pourrait egalement appuyer l'hypothese de la deterioration des conditions hivernales pour les guillemots. Du plastique a egalement ete retrouve dans 15 % des oiseaux, et 53 % etaient parasites par des nematodes. [Traduit par la Redaction] Mots-cles: alimentation hivernale des oiseaux marins, guillemot de Brunnich, Uria lomvia, sud-ouest du Groenland, borealisation, krill, capelan, Mallotus villosus., Introduction For migratory bird populations, the non-breeding season represents a very long and usually challenging period of their annual cycle, and their survival and subsequent breeding performance are highly dependent [...]

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]

ABSTRACT Aim Location Taxa Methods Results Main Conclusions Ecologically similar species living in sympatry are expected to segregate to reduce the effects of competition where resources are limiting. Segregation from heterospecifics commonly occurs in space, but it is often unknown whether such segregation has underlying environmental causes. Indeed, species could segregate because of different fundamental environmental requirements (i.e., ‘niche divergence’), because competitive exclusion at sympatric sites can force species to either change the habitat use they would have at allopatric sites (i.e., ‘niche displacement’) or to avoid certain areas, independently of habitat (i.e., ‘spatial avoidance’). Testing these hypotheses requires the comparison between sympatric and allopatric sites. Understanding the competitive mechanisms that underlie patterns of spatial segregation could improve predictions of species responses to environmental change, as competition might exacerbate the effects of environmental change.North Atlantic and Arctic.Common guillemots Uria aalge and Brünnich's guillemots Uria lomvia.Here, we examine support for these explanations for spatial segregation in two closely‐related seabird species, common guillemots (Uria aalge) and Brünnich's guillemots (U. lomvia). For this, we collated a pan‐Atlantic data set of breeding season foraging tracks from 1046 individuals, collected from 20 colonies (8 sympatric and 12 allopatric). These were analysed with habitat models in a spatially transferable framework to compare habitat preferences between species at sympatric and allopatric sites.We found no effect of the distribution of heterospecifics on local habitat preferences of the focal species. We found differences in habitat preferences between species, but these were not sufficient to explain the observed levels of spatial segregation at sympatric sites.Assuming we did not omit any relevant environmental variables, these results suggest a mix of niche divergence and spatial avoidance produces the observed patterns of spatial segregation. [ABSTRACT FROM AUTHOR]

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]

Density-dependent prey depletion around breeding colonies has long been considered an important factor controlling the population dynamics of colonial animals. 1–4 Ashmole proposed that as seabird colony size increases, intraspecific competition leads to declines in reproductive success, as breeding adults must spend more time and energy to find prey farther from the colony. 1 Seabird colony size often varies over several orders of magnitude within the same species and can include millions of individuals per colony. 5,6 As such, colony size likely plays an important role in determining the individual behavior of its members and how the colony interacts with the surrounding environment. 6 Using tracking data from murres (Uria spp.), the world's most densely breeding seabirds, we show that the distribution of foraging-trip distances scales to colony size0.33 during the chick-rearing stage, consistent with Ashmole's halo theory. 1,2 This pattern occurred across colonies varying in size over three orders of magnitude and distributed throughout the North Atlantic region. The strong relationship between colony size and foraging range means that the foraging areas of some colonial species can be estimated from colony sizes, which is more practical to measure over a large geographic scale. Two-thirds of the North Atlantic murre population breed at the 16 largest colonies; by extrapolating the predicted foraging ranges to sites without tracking data, we show that only two of these large colonies have significant coverage as marine protected areas. Our results are an important example of how theoretical models, in this case, Ashmole's version of central-place-foraging theory, can be applied to inform conservation and management in colonial breeding species. [Display omitted] • The distribution of foraging trips around murre colonies scaled to colony size0.33 • Colony size can be used to predict foraging areass over a large geographic scale • Foraging areas of most North Atlantic murre breeding populations are not within protected areas Seabird colony size can vary over several orders of magnitude. Colony size likely plays an important role in determining individual behavior. Using tracking data from murres, the world's most densely breeding seabirds, Patterson et al. show how the distribution of foraging-trip distances scales to colony size, consistent with Ashmole's halo theory. [ABSTRACT FROM AUTHOR]