Vegard Sandøy Bråthen

Countries have committed to expanding the marine protected area (MPA) network to 30% of the world's ocean by 2030, more than tripling current coverage, and focusing on areas important for biodiversity. For such expansion to translate into effective conservation of marine biodiversity, it must rely on the best available knowledge. Here, we analyze tracking data on > 13,000 individuals (44 species, eight families) to map the distribution of highly mobile seabirds in the Atlantic Ocean and adjacent seas throughout the year. We identify regions important year‐round or seasonally. The High Seas are as important as national waters for highly mobile seabirds but are even less protected. Current Atlantic MPAs hold < 14% of tracked species density, but their expansion to 30% of the ocean could protect up to two thirds. We share this new knowledge layer to support national and international efforts and policies to strategically expand the Atlantic MPA network.

Diel rhythms synchronized to Earth’s photic cycle are near-ubiquitous among animals living in regions with distinct day–night cues. Where such cues are reduced or absent, however, activity patterns may weaken, reorganize or become decoupled from the light–dark cycle, which may allow for more flexible behavioural expression. Using a dataset of >900 free-ranging black-legged kittiwakes from colonies spanning a broad latitudinal gradient (40–81°N), we show considerable population-level variation in diel activity patterns, from clear 24 h rhythms with distinct peaks at dawn and dusk at lower latitudes, to variable and non-diel rhythms with flattened activity patterns across the 24 h day at high latitudes. These patterns were consistent with the wide spectrum of light–dark cycles experienced across their breeding range, supported by our finding that activity was strongly predicted by sun elevation, suggesting alignment with the light–dark cycle. Together, our findings reveal substantial within-species variation in rhythmicity across latitudes and demonstrate that changes in the photic environment can reshape the temporal organization of activity even within a single, widely distributed species.

Trace elements occur naturally in the environment, but anthropogenic activities can amplify their release, increasing exposure and bioaccumulation in marine predators such as seabirds. Mercury (Hg) in liver, blood, and eggs of Leach’s storm-petrels (Hydrobates leucorhous), has been investigated as a short-term exposure indicator of hatching and fledging success. However, chronic Hg intake and exposure to other trace elements during the non-breeding period, remain poorly understood. This study assessed geographic variation in trace element exposure and relative trophic position in Leach’s storm-petrels from five overwintering locations in the Atlantic Ocean, using secondary feathers (S4s) and geolocation data. Hg concentrations and trophic position (δ15N) varied significantly among overwintering locations, whereas other trace elements varied without clear spatial patterns. Sea surface temperature was positively correlated with Hg concentrations, whereas dietary origin (δ13C) and year were associated with relative trophic position. Colony of origin had no effect on Hg or trophic position, likely reflecting high intra-colony variability in wintering locations. Additionally, Hg concentrations were highest in birds overwintering in oligotrophic regions where δ¹⁵N values were low, suggesting lower nitrogen baselines in areas dominated by diazotrophic organisms and enhanced methylmercury availability via sulfate-reducing bacteria. In contrast, storm-petrels overwintering in productive upwelling regions such as the Benguela system exhibited lower Hg concentrations, consistent with Hg biodilution driven by rapid decaying phytoplankton export to deep sediments. These findings provide baseline information on trace element exposure during the non-breeding period of Leach’s storm-petrels and inform future studies on migratory carry-over effects influencing adult survival and reproductive success.

Many countries are developing offshore wind farms to provide renewable energy, yet such developments can harm biodiversity. Seabirds are a highly threatened group of birds and can be impacted by wind farms through lethal collisions and via sub‐lethal displacement effects. However, we do not have a comprehensive understanding of the impacts of offshore wind farms on seabird populations, particularly outside of the breeding season. We developed an individual‐based model to predict the non‐breeding season impacts of offshore wind farms on seabirds. We used long‐term tracking data obtained from geolocation‐immersion loggers to estimate population‐level distributions and activity budgets. We simulated individual behaviour, movement, wind farm interactions (collision and displacement) and any resulting lethal or sub‐lethal effects. We demonstrated our model by assessing the impact of 10 simulated offshore wind farms on two populations that breed in Norway: common guillemots Uria aalge (Sklinna) and black‐legged kittiwakes Rissa tridactyla (Ålesund). We quantified collision risk in kittiwakes and sub‐lethal displacement effects in guillemots and converted these effects into a change in survival or end of season body mass as a proxy for condition. We predicted that 49.6% of guillemots breeding at Sklinna would experience displacement effects during the non‐breeding season. As the energetic impact of displacement is relatively unknown, we modelled a range of possible displacement costs and present several impact scenarios, with adult mortality levels ranging from 0% to 5.32% and end of season body masses of 97.12%–99.84% compared to those resulting from an unimpacted scenario. Despite 98.9% of kittiwakes flying through at least one wind farm footprint, we only predicted collisions in 0.055% of the population; this low mortality was primarily driven by low overlap between the modelled height of the turbine rotors and the probable flight height of kittiwakes. Practical implication: Our model provides a tool that can be used to assess the non‐breeding season impacts of OWFs on seabird populations, improving sustainability when developing renewable energy infrastructure. We highlight several key limitations as areas of research that are required to reduce uncertainty when predicting impacts. Our model is reproducible and adaptable for use on other species or for other marine threats.

Coastal zones are heavily impacted by anthropogenic development. However, they are also important habitats for seabirds, some of which are coastal year-round. We investigated the non-breeding season distribution and activity patterns of black guillemots ( Cepphus grylle ), a year-round coastal seabird species, from two colonies in central/northern Norway over multiple years using geolocator loggers equipped with wet-dry sensors. Migratory behaviour differed among birds from the two colonies. Birds from Røst (67.5°N, 12.0°E) travelled on average further (mean 283 km; max 1008 km) and to more southerly wintering areas than those from Sklinna (65.2°N, 11.0°E), which remained closer to the colony (mean 97 km; max 118 km). Birds from both colonies wintered along coastal stretches of Norway that are characterized by a high islet density and kelp forests, which appear to be important habitat characteristics for black guillemots year-round. Individuals tracked over multiple years showed an intermediate to high repeatability in migration movements. Saltwater immersion data suggested that birds used twilight periods to forage during the winter months, especially at higher latitudes. This suggests that reduced daylength and low temperatures constrained black guillemots to use suboptimal light conditions for foraging. Our study adds important and management-relevant knowledge about the non-breeding season movements and activity patterns of black guillemots.

Climate-driven ocean warming is profoundly reshaping marine ecosystems, with cascading effects on biodiversity and trophic interactions. For migratory marine predators such as seabirds, demographic responses to warming depend on when and where populations are exposed across the annual cycle. Therefore, integrating demographic monitoring and tracking data, across broad geographic and temporal scales, is essential, given the spatial and seasonal variability in ocean warming. Here, we integrated long-term demographic data, seasonal distributions, and sea surface temperatures (SSTs) for 26 populations of five seabird species breeding in the North–East Atlantic to assess the effects of SSTs on reproduction, survival, and population growth trajectories. Demographic responses varied widely among populations and seasons, but negative effects were most consistently associated with warming during the autumn period postbreeding, particularly in the Barents and East Greenland Seas. Winter warming also corresponded to reduced survival, while breeding-season SSTs showed fewer significant effects on reproductive rates. Populations with dual responses to warming in both the breeding and nonbreeding seasons had the lowest projected population growth rates under future SSTs given a high emissions scenario. These results demonstrate that population vulnerability reflects the interaction between seabirds’ year-round distributions and regional ocean warming. This underlines the need to integrate year-round tracking and long-term monitoring to inform conservation strategies and marine spatial planning to ensure climate-resilient marine ecosystems.

Background: Breeding pelagic seabirds feed over wide areas. Their diet and space use can therefore provide proxies for otherwise be difficult to observe environmental conditions but interpretation of these proxies requires knowledge of foraging range. Antarctic sea ice regulates global climate, but a paucity of data on its past extent causes uncertainty in climate reconstruction and prediction. Deposits of stomach oils, produced defensively by snow petrels Pagodroma nivea (near-obligate sea-ice foragers), reflect sea ice conditions, sometimes over tens of millennia, but spatial interpretation of these biological archives is hampered by lack of data on foraging range, and how this varies seasonally, among colonies and with sex. Methods: We tracked 34 and 60 snow petrels using light-based geolocators and GPS loggers, respectively to estimate foraging ranges at three colonies located 180-200 km inland in Dronning Maud Land. We tested whether foraging latitude is associated with ice edge latitude, estimated via satellite remote sensing. We then projected potential foraging ranges for all known colonies on the study area to reexamine assumptions made in paleoclimate studies. Results: During most breeding stages, and across breeding seasons, core home ranges were centred approximately 2 degrees south of the outer sea-ice edge and tracked this habitat as it receded during the spring melt. Females were approximately 7% lighter than males but foraged at similar distances and in similar areas. Foraging ranges differed little between colonies but substantially between breeding stages. For example, median range was ~1,400 km during the pre-laying exodus vs. ~550 km during brood-guard. Conclusions: Snow petrel stomach-oil deposits potentially integrate environmental conditions over greater and more seasonally variable areas than previously assumed, probably with a bias towards conditions in the outer Marginal Ice Zone during the early summer when stomach oil deposition due to nest competition is likely greatest. Projected potential home ranges of snow petrel colonies in the western Weddell Sea suggest that breeding is limited by access to foraging habitat, such as coastal polynyas. We hypothesise that as sea ice fluctuated over previous glacial-interglacial cycles, this also regulated breeding distribution across the region.

The ratio of the innate heterophils to the acquired lymphocytes (the H/L-ratio) has been advocated as a good indicator of physiological stress. Little is known, however, about their development in wild birds. The present study investigates how leucocyte profiles develop in nestlings of a long-lived seabird, the Black-legged Kittiwake (Rissa tridactyla). We counted blood leucocytes in nestlings of about 10 and 25 days of age (n = 23), and in breeding adults around the time of hatching (n = 40) and calculated the H/L-ratio for all three groups. We further investigated if any variation in the leucocyte counts could be explained by body condition or the stress-related hormone corticosterone. 10-day-old nestlings in better body condition showed greater investment in heterophils, which increased their H/L-ratio. The initial focus on innate immunity shifted towards acquired immunity by 25 days, aligning their H/L-ratio with that of adults. In adult Kittiwakes, however, better body condition correlated with lower H/L-ratio, the reverse of the pattern in young nestlings, and this variation was not linked to stress hormone (corticosterone) levels. Overall, our findings suggest that the H/L-ratio reflects the ontogeny of physiological traits and individual condition. As an indicator, values must be interpreted depending on age, in which its sensitivity may also vary. As such, the H/L-ratio may not always be a reliable indicator of physiological stress, in particular related to the release of glucocorticoid hormones.

In seasonal environments, the fitness of animals depends upon the successful integration of life‐history stages throughout their annual cycle. Failing to do so can lead to negative carry‐over effects where individuals are transitioning into the next season in different states, consequently affecting their future performance. However, carry‐over effects can be masked by individual quality when individuals vary in their efficiency at acquiring resources year after year (i.e. ‘quality’), leading to cross‐seasonal consistency in individual performance. Here we investigated the relative importance of carry‐over effects and individual quality in determining cross‐seasonal interactions and consequences for breeding success over the full annual cycle of a migratory seabird (black‐legged kittiwake Rissa tridactyla). We monitored the reproduction and annual movement of kittiwakes over 13 years using geolocators to estimate their breeding success, distribution and winter energy expenditure. We combined this with an experimental approach (clutch removal experiment, 2 years) to manipulate the reproductive effort irrespective of individual quality. Piecewise path analyses showed that successful breeders reproduced earlier and were more likely to breed successfully again the following year. This positive interaction among consecutive breeding stages disappeared after controlling for individual quality, suggesting that quality was dominant in determining seasonal interactions. Moreover, controlling experimentally for individual quality revealed underlying carry‐over effects that were otherwise masked by quality, with breeding costs paid in higher energy expenditure and delayed onset of reproduction. We highlight the need to combine an experimental approach along with long‐term data while assessing apparent carry‐over effects in wild animals, and their potential impact on fitness and population demography.

Mercury (Hg) is a heterogeneously distributed toxicant affecting wildlife and human health. Yet, the spatial distribution of Hg remains poorly documented, especially in food webs, even though this knowledge is essential to assess large-scale risk of toxicity for the biota and human populations. Here, we used seabirds to assess, at an unprecedented population and geographic magnitude and high resolution, the spatial distribution of Hg in North Atlantic marine food webs. To this end, we combined tracking data of 837 seabirds from seven different species and 27 breeding colonies located across the North Atlantic and Atlantic Arctic together with Hg analyses in feathers representing individual seabird contamination based on their winter distribution. Our results highlight an east-west gradient in Hg concentrations with hot spots around southern Greenland and the east coast of Canada and a cold spot in the Barents and Kara Seas. We hypothesize that those gradients are influenced by eastern (Norwegian Atlantic Current and West Spitsbergen Current) and western (East Greenland Current) oceanic currents and melting of the Greenland Ice Sheet. By tracking spatial Hg contamination in marine ecosystems and through the identification of areas at risk of Hg toxicity, this study provides essential knowledge for international decisions about where the regulation of pollutants should be prioritized.