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Chemical dispersion is an oil spill response strategy where dispersants are sprayed onto the oil slick to enhance oil dispersion into the water. However, accidental application could expose seabirds to dispersants, thereby negatively affecting their plumage. To understand the possible impacts on seabirds, feathers from common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) were exposed to different dosages of the dispersant Dasic Slickgone NS. For all exposure dosages the feathers increased in weight, and mostly for common eider. Analysing the feather microstructure, e.g., the Amalgamation Index, showed that larger damages were found on thick-billed murre than common eider. A no-sinking limit was established at 0.109 ml/m 2 . Relating this value to desktop simulations of potential sea-surface dosages in real-life situations, and to published accounts of response operations, showed that the limit is likely to be exceeded. Thus, our results show that chemical dispersants in realistic dosages could impact seabirds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

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 size 0 .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., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Naturally occurring radionuclides, in particular, polonium-210 ( 210 Po), have a greater contribution than anthropogenic radionuclides to the annual effective dose received by the general public due to consumption of seafood. Knowledge of potential trophic sources and transfer of 210 Po to seabird species and subsequently to the Greenlandic people is, however, still poor. Here, we assess the transfer of 210 Po and 210 Pb to seabirds sampled during autumn and winter 2017 and 2018 in Greenland and provide a dose assessment. The activity concentrations of 210 Po in muscle and liver, respectively, ranged from 0.2 ± 0.1 Bq kg - 1 w.w. in glaucous gull (Larus hyperboreus) to 21.2 ± 22.6 Bq kg - 1 w.w. in thick-billed murre (Uria lomvia) and from 32.0 ± 9.4 Bq kg - 1 w.w. in common eider (Somateria mollissima) to 40.5 ± 49.0 Bq kg - 1 w.w. in thick-billed murre. 210 Po was non-uniformly distributed in the body of thick-billed murre. Kidneys and feathers showed higher 210 Po activity concentrations than heart and bone. The 210 Po/ 210 Pb activity concentration ratios are higher than unity, indicating that 210 Po is preferentially taken up by seabirds compared to its progenitor 210 Pb. The derived annual absorbed dose from 210 Po to the whole body of thick-billed murre was 6.4 × 10 2  ± 3.0 × 10 2 μGy. The annual effective dose to the average adult and representative person in Greenland due to ingestion of 210 Po in seabirds was estimated to 13.0 μSv and 57.0 μSv, respectively. This derived dose is low and poses a slight risk, and risk communication is therefore deemed unnecessary., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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 Alcatorda, common guillemot Uriaaalge 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.