United States

**Abstract:**

A recent decline in the Norwegian populations of Brünnich&#39;s and common guillemots, the largest living auks and constituting a substantial amount of North Atlantic seabird biomass, is causing considerable concern. Both species share a very special, semi-precocious breeding strategy with the single chick spending roughly a month on narrow cliff ledges before jumping off while still unable to fly and moving out to sea accompanied by its father. The chicks fledge somewhere on the open ocean. Where they go and how they spend this second half of their rearing period has always been a mystery. With dramatic increases in human impact and activity in the world&#39;s oceans over the last decades, it has thus become paramount to document this crucial part of the guillemot life cycle to be able to successfully preserve these threatened species. In this study, we documented and quantified for the first-time the swimming migration of guillemot chicks from when they left the breeding ledge until fledging. To do this, we attached satellite transmitters to chicks of both species immediately before jumping at a high-Arctic colony where they breed sympatrically (Bjørnøya, 74.5°N 18.9°E). At the same time, we attached time-depth recorders to the accompanying fathers to determine the time spent until fledging. Chicks of both species moved rapidly away from the colony at an average speed of 22 to 27 km d-1 along clearly defined routes. For both species, the migration to species-specific autumn staging areas lasted about 2 to 4 weeks. As such, what is an extremely vulnerable period for guillemots is now clearly defined and seems predictable in both space and time. As a result, decisive areal planning of human activities in the areas involved is now possible to mitigate negative impacts on these species.

**Authors:**

Benjamin Merkel¹, Hallvard Strøm²

¹Akvaplan-niva, ²Norwegian Polar Institute

3rd World Seabird Conference

A mystery solved - How and where do guillemot chicks spend their second half of their rearing period?

Welcome Seabirders!  

Welcome to Virtual World Seabird Conference 3 - vWSC3! Whether you are in your office or lab, at home, in a coffee shop or bar poaching some wifi, or at a remote field site or research vessel – we are very excited to welcome you to the third ever World Seabird Conference. 

We would like to thank ALL of you for being so patient as WSC3 was scheduled, postponed, rescheduled, revised to virtual, and scheduled again. Throughout all those iterations there was one message that remained perfectly clear – seabirders were eager to meet and share their science. If we could not meet in person then virtual it would have to be, but a 3rd WSC was something everyone wanted. That support and commitment helped the WSU Board of Directors and Member Societies sort through all of the challenges they faced to plan and hold this conference. 

The list of those that need to be thanked is long and, while we plan on recognizing many during the live closing plenary, it is important to do so here in writing as well. 

The Australasian Seabird Group was our Local Host for our plan to meet in Hobart, Tasmania. They invested substantial time and effort to find venues and plan events that we unfortunately were not able to visit. Nonetheless we appreciate their work on behalf of WSC3 and encourage all of you to thank them when you see their members in Gathertown or elsewhere during our virtual meeting. Their willingness to host created the initial excitement for WSC3 and without that our vWSC would not have been possible.

We also wish to thank the Science Program Committee, the Virtual Committee, and the Early Career Scientist Committee for their hard work planning the logistics, events, and schedule for vWSC3. These committees also had to deal with changing parameters and short timelines that made what is always a challenging task even more challenging. The Travel Awards Committee also invested time and effort in developing procedures for awarding travel funds that ultimately would not be implemented. 

Our ability to shift from an in-person to a virtual meeting, and to do so in a way that would be financially feasible, was due to the effective efforts of The International Fundraising Committee and to our financial sponsors. The IFC raised funds to support WSC3 and then, through the good relationships they built with sponsors, ensured we could re-envision how those funds could be used to support a virtual conference that would be affordable and high-quality.

We all owe the WSU Board of Directors and the Representatives of the Member Societies a great deal of thanks. They are the ones who manage the WSU and, for the past 18 months, have had to have a series of challenging meetings and conversations, have had to make a series of difficult choices, have had to do all of that while considering the short- and long-term health of WSU and the World Seabird Conferences, and did this while also managing their own challenges at their day jobs. We are grateful for their diligence, patience, foresight, and throughout all of the meetings, their collegiality. Also – a 6-year term is quite a commitment!

There would not be a WSC3 without a successful WSC1 and WSC2. Thanks go to the Pacific Seabird Group for their support of WSC1 in Victoria, Canada, and to the African Seabird Group for their support of WSC2 in Cape Town, South Africa. In each of these endeavors and for our current conference we were fortunate to work with a dependable and trustworthy partner in Podium Conferences. Michelle Smith and Marischal de Armond have become valued members of our team and have not only helped us plan conferences but have assisted and advised the WSU Chairs and Board on issues above and beyond conference planning. 

As we embark on our vWSC3 week we extend to all of you our thanks for showing up, for being patient, and most importantly for the work you do with seabirds. We are all part of a unique, global community that shares an interest, a fascination, and a passion for birds that make a living in our world’s oceans. We have advanced the science, conservation, and management of seabirds as well the ecosystems they inhabit. We are consistently impressed and motivated by the work you do. 

The WSU formed in 2010 because we saw the need for a global organization to address challenges at a global level. Over the past 11 years WSU has grown, adapted, and evolved to become the community that this week is making vWSC3 a reality. Enjoy the week, appreciate and support the friends and colleagues you have made in the community, and if you see us in a virtual hallway please stop and say hello! 

Thank you for the opportunity to serve all of you and the WSU over the past few years,

Nicholas Carlile, Interim Chair, WSU<br>
Patrick Jodice, 2nd Chair of the WSU<br><br>

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Join us for four days of science, networking and virtual engagement with delegates from around the world!

**Abstract:**

A recent decline in the Norwegian populations of Brünnich's and common guillemots, the largest living auks and constituting a substantial amount of North Atlantic seabird biomass, is causing considerable concern. Both species share a very special, semi-precocious breeding strategy with the single chick spending roughly a month on narrow cliff ledges before jumping off while still unable to fly and moving out to sea accompanied by its father. The chicks fledge somewhere on the open ocean. Where they go and how they spend this second half of their rearing period has always been a mystery. With dramatic increases in human impact and activity in the world's oceans over the last decades, it has thus become paramount to document this crucial part of the guillemot life cycle to be able to successfully preserve these threatened species. In this study, we documented and quantified for the first-time the swimming migration of guillemot chicks from when they left the breeding ledge until fledging. To do this, we attached satellite transmitters to chicks of both species immediately before jumping at a high-Arctic colony where they breed sympatrically (Bjørnøya, 74.5°N 18.9°E). At the same time, we attached time-depth recorders to the accompanying fathers to determine the time spent until fledging. Chicks of both species moved rapidly away from the colony at an average speed of 22 to 27 km d-1 along clearly defined routes. For both species, the migration to species-specific autumn staging areas lasted about 2 to 4 weeks. As such, what is an extremely vulnerable period for guillemots is now clearly defined and seems predictable in both space and time. As a result, decisive areal planning of human activities in the areas involved is now possible to mitigate negative impacts on these species.

**Authors:**

Benjamin Merkel¹, Hallvard Strøm²

¹Akvaplan-niva, ²Norwegian Polar Institute

technical paper

**Abstract:**

Many North Atlantic populations of thick-billed murres Uria lomvia are declining rapidly. Specifically, all populations wintering off West Greenland are declining, whereas most populations wintering off Atlantic Canada are stable. Murres are migratory and often cross international boundaries between their breeding and wintering areas. We have aimed to understand the impact of the various potential drivers of this decline, most importantly human harvest and climate change-related variation in oceanographic conditions in the wintering areas. Oceanographic conditions, including the state of the North Atlantic Subpolar Gyre, are hypothesized to affect food availability, energy costs and thus energy balance and survival. We have used a variety of approaches to quantify the importance of various drivers for murre population growth. Population models indicate that low pre-breeding survival may be responsible for the observed large-scale declines. In early 2022, we bring together researchers and representatives of management agencies from four countries to present results of the project and discuss options for coordinated cross-boundary management, potentially a legally binding international management plan.

**Authors:**

Morten Frederiksen¹, Sébastien Descamps², Kyle Elliott³, Jérôme Fort⁴, Nicholas Huffeldt⁵, Aili Labansen⁵, Jannie Linnebjerg¹, Flemming Merkel¹, Gregory Robertson⁶, Thorkell Thorarinsson⁷

¹Aarhus University, ²Norwegian Polar Institute, ³McGill University, ⁴Université La Rochelle, ⁵Greenland Institute of Natural Resources, ⁶Environment Canada, ⁷Northeast Iceland Nature Centre

From research to cross-boundary management action: addressing the decline of the thick-billed murre in the North Atlantic

**Abstract:**

The Mascarene Petrel (Pseudobulweria aterrima) is a critically endangered seabird, endemic to Reunion island (Western Indian ocean island). It is one of the rarest and most endangered birds in the world belonging to the least known seabird genus. The species was supposed to be extinct for 80 years, before being rediscovered in 1970 with a grounded bird. Then, it was only known by several grounded birds and a few flight calls recorded in 2001 but no information was existing on basic breeding biology. The efforts implemented by the collaborative LIFE Petrels program initiated in 2014, allowed us, in 4 years, to collect a lot of scientific knowledge on biology, breeding behaviour and habitat selection. In this study, we focuson the breeding activity, using song recorders and camera traps, in order to describe it for the first time. We recorded and analysed up to 30 000 hours at 121 different locations all the years long and detected more than 120 000 vocalisations since 2015. The use of camera traps on the first two colonies discovered during breeding season 2016/2017 allowed us to analyse up to 5 300 videos which revealed more than 3 800 Mascarene Petrel behaviour. We will present here for the first time the most complete vocal repertory of the species (flight vs ground calls, male vs female, intraspecific interactions) and vocal activity pattern for night, season and moon phases. Finally, we will describe breeding phenology and differences in both colonies surveyed (20 km apart) explaining the 3 months fledgling period.

**Authors:**

Jerome Dubos¹, Patrick Pinet², Martin Riethmuller³, Yahaïa Soulaimanay Mattoir³, Fabien Jan³, François-Xavier Couzi³, Matthieu Lecorre⁴

¹Université de La Réunion (UMR ENTROPIE), ²Parc national de La Réunion, ³SEOR, ⁴Université de La Réunion

Discovery of phenology and breeding behaviour of the critically endangered Mascarene Petrel (Pseudobulweria aterrima) on La Réunion

**Abstract:**

Current knowledge is inadequate to safeguard seabird populations from impacts of oil spills, overfishing, displacement and collision risk at marine renewable installations. This gap is to a large extent driven by the fact that standard statistical models applied to survey data provide limited documentation of the fine-scale distributional dynamics and patchiness of seabirds. Here, a new dynamic modelling framework solution is presented for prediction of fine-scale concentrations and movements of seabirds in close-to-real time using fully integrated 3-D hydrodynamic models, dynamic habitat suitability models and agent-based models. The modelling framework has been developed and validated for seabirds in the Barents Sea where available seabird survey data are fragmented. Long-term (10 years) dynamic patterns describing currents and winds at hourly intervals were extracted from a 3-dimensional hydrodynamic module calibrated against local measurements. Long-term patterns of habitat suitability were deduced from dynamic distribution models describing the correlation between surveyed densities and water mass and frontal characteristics extracted at hourly intervals from the hydrodynamic module. Long-term movement patterns and energetics were quantified using agent-based models which integrated the modelled timeseries of currents, winds, sea temperature and habitat suitability. The oceanographic and habitat predictions were validated against independent measurements and observations, which were not used in the parameterisation of the models. The model results underline that model complexes integrating high-resolution hydrodynamic, distribution and agent-based models constitute an improved basis for undertaking more precise assessments of the risk of seabirds from anthropogenic pressures in the future.

**Authors:**

Henrik Skov¹, Teo Theophilus², Mads Madsen¹, Thomas Uhrenholdt¹, Frank Thomsen¹, Jonas Mortensen¹, Per Fauchald³, Stefan Heinänen⁴

¹DHI, ²DHI Water & Environment Pte. Ltd., ³Norwegian Institute for Nature Research, ⁴Novia University of Applied Sciences

Real-time predictions of seabird distribution offer improved basis for risk assessments in the future

**Abstract:**

The Ivory Gull (Pagophila eburnea) is among the rarest seabirds. It is associated with sea-ice throughout the year and breeds at high latitudes in Arctic Canada, Greenland, Svalbard and the northern islands of Russia in the Barents and Kara seas. It nests in mainly small (i.e., 5 to 200 pairs), scattered colonies and there is growing international concern regarding declining population trends. In response, an international circumpolar ''Ivory Gull Conservation Strategy and Action Plan'' has been presented by the Arctic Council to generate new research into how this bird is responding to increases in the disappearance of sea ice habitat, natural resource exploration, and contaminants. Here we present recent findings from Canada. The Canadian population of Ivory Gulls has declined by 70 % since the 1980s at colonies that were known to exist before 2002. Recent aerial surveys conducted by us in 2019 indicate that the population has not recovered, and further, suggests that the breeding range of the species has contracted northward. Satellite tracking of Ivory Gulls from Arctic Canada shows that they migrate to winter in Davis Strait and Labrador Sea which has recently been confirmed as a key wintering area for the species in the Atlantic. As a top-predator and scavenger, the ivory gull is vulnerable to contaminants that concentrate through the food chain (biomagnifying contaminants). In Arctic Canada, the levels of pesticides in ivory gulls (including organochlorinated pesticides (OCPs), DDT and polychlorinated biphenyls (POPs)) and a heavy metal (mercury) are among the highest ever reported in arctic seabirds.

**Authors:**

Grant Gilchrist¹, Mark Mallory²

¹Government of Canada, ²Acadia University

Conservation biology of the endangered Ivory Gull in Arctic Canada

**Abstract:**

In nutrient-depleted coastal waters, supply is principally dependent on allochthonous sources, such as seabird excretions. Among seabirds, penguins are the largest contributors to nutrients worldwide although most of their populations are decreasing rapidly. It is therefore important to understand their contribution to the cycle of nitrogen (N) and phosphorus (P) in coastal ecosystems, to then predict the potential consequences of their losses. We quantified the N and P production at the world's largest African penguin (Spheniscus demersus) colony in Algoa Bay, South Africa. We modeled the fate of these nutrients using the Generation of emissions from Uric Acid Nitrogen Outputs model (GUANO). Then, we explored the potential effects of penguin excreta on the dissolved inorganic N and P in the water, and production (chlorophyll-a, the biomass of zooplankton and larval fish density) in an area close (200m) and far (2km) from the colony. Penguins excreted annually a total of 45.35 tons of N and 8.39 tons of P. Most of the N excreted was volatilized (57-76 % in NH3t ), and only a small quantity was washed off into the ocean ( 5-20% washed as total ammoniacal). Precipitations and the amount of humidity in the air triggered both processes. Following previous results, concentrations of N, P and productivity were similar close (200 m) and farther (2 km) from the colony, suggesting a limited influence of penguin excreta on the immediate marine environment. Compared to other sources of nutrients, the amounts of N and P excreted by penguins were similar to the closest estuaries but smaller compared to the sewage loadings. Industrial and domestic sewages loaded in the bay up to eight times more N and five times more P than the amounts produced by penguins. These numbers raise our concerns about a potential imbalance in stochiometry of nutrients and the risk of eutrophication of waters near the colony.

**Authors:**

Giannina Passuni¹, Lucienne Human², Stuart Riddick³, Mfundo Bizani², Paula Pattrick², Shaun Deyzel², Tommy Bornman², Lorien Pichegru⁴

¹University of Hamburg, ²South African Environmental Observation Network, Elwandle Coastal Node, ³Department of Civil and Environmental Engineering, Princeton University, ⁴Nelson Mandela University

Is the world?s largest African penguin colony influencing productivity in the near shore waters?

**Abstract:**

The rapidly changing climate in the Arctic is expected to have significant impacts on seabird foraging ecology, mediated through changes in the distribution and abundance of their prey but also the distribution of competitors (e.g. with southerly species expanding into the Arctic). Here we study how the environment and competition interactions affect the foraging ecology and abundance of two closely related species breeding in sympatry in several colonies around the Arctic: the common guillemot (a temperate species) and Brünnich's guillemot (an Arctic species). For this, we tracked the two species during the breeding season with GPS and temperature-depth recorders at five colonies around Iceland, which is surrounded by contrasted marine environments (due to different cold and warm currents). We relate the habitat use of the two species to available environmental conditions around each site and colony size. We then relate population counts and trends to surrounding temperature and competition. We find different foraging behaviours and different degrees of overlap between the two species among the different sites, but not always more pronounced segregation in the biggest colony. Nevertheless, even though we found evidence of segregation at most sites, we did not find any effect of competition at the population level.

**Authors:**

Anne-Sophie Bonnet-Lebrun¹, Jason Matthiopoulos², Þorkell Þórarinsson³, Yann Kolbeinsson³, Thomas Larsen⁴, Patrick Roberts⁴, Morten Frederiksen⁵, Aude Boutet¹, Derren Fox¹, Tim Morley¹, Kirsty Franklin⁶, Kayleigh Jones¹, Erpur Hansen⁷, Norman Ratcliffe¹

¹British Antarctic Survey, ²Institute of Biodiversity, Animal Health and Comparative Medicine, ³Northeast Iceland Nature Research Centre, ⁴Max Planck Institute for the Science of Human History, ⁵Aarhus University, ⁶University of East Anglia, ⁷South Iceland Nature Research Centre

Using multi-colony tracking to understand the foraging ecology of two sympatrically breeding auks around Iceland

**Abstract:**

Seabirds are highly mobile animals, flying vast distances across open oceans on a single foraging trip or a long migration journey. Identifying the drivers of seabird movements, and the fitness consequences of variation in these movements, is key to understanding the mechanisms shaping their ecology and ultimately to predict how their distribution and populations may be affected by environmental change. Multi-colony studies are a powerful tool to identify large-scale ecological drivers of seabird movement, measure variation between populations and understand how these may affect population dynamics. I illustrate this claim with three examples of multi-colony studies I have recently been leading, from a small-scale comparison of two populations to an ocean-wide study, all of which have yielded important ecological findings. First, studying the spatial ecology and breeding behaviour of two seemingly similar populations of tropicbirds in the Indian Ocean reveals stark differences between the two locations, suggesting underlying differences in environmental conditions and highlighting the need for distinct conservation approaches. Second, a larger-scale comparison of the foraging ecology of four colonies of Atlantic puffins in the UK, Iceland and Norway with different population trends and breeding performance helps us to identify drivers of population declines. Finally, a species-wide study of thirteen puffin colonies across the North Atlantic unveils key ecological drivers of migration.

**Authors:**

Annette Fayet¹

¹University of Oxford

Drivers of seabird movements and their fitness consequences: insights from multi-colony tracking

**Abstract:**

Migration is a widespread strategy for escaping unfavourable conditions during winter, but the extent to which populations that segregate during the breeding season aggregate during the non-breeding season is poorly understood. Whilst segregation may be associated with higher overall likelihood of overlap with threats, but fewer populations affected, aggregation may result in a lower probability of exposure to threats, but higher overall severity. We investigated non-breeding distributions and extent of population aggregation in two sympatrically breeding auks. We deployed geolocators-immersion loggers on common guillemots Uria aalge and razorbills Alca torda at eleven colonies around the north of the UK and tracked their movements across two non-breeding seasons (2017-18; 2018-19). Using 290 guillemot and 135 razorbill tracks, we mapped population distributions of each species and compared population aggregation during key periods of the non-breeding season: post-breeding moult and mid-winter, observing clear interspecific differences. Razorbills were largely distributed in the North Sea, whereas guillemot distributions were spread throughout Scottish coastal waters and the North, Norwegian and Barents Seas. We found high levels of aggregation in razorbills and a strong tendency for colony-specific distributions in guillemots. Therefore, razorbills are predicted to have a lower likelihood of exposure to marine threats, but more severe potential impact due to the larger number of colonies affected. This interspecific difference may result in divergent population trajectories, despite the species sharing protection at their breeding sites. We highlight the importance of taking whole-year distribution into account in spatial planning to adequately protect migratory species.

**Authors:**

Lila Buckingham¹, Maria Bogdanova¹, Jonathan Green², Bob Furness³, Francis Daunt¹

¹UK Centre for Ecology and Hydrology, ²University of Liverpool, ³MacArthur Green

Interspecific variation in non-breeding aggregation: a multi-colony tracking study of two sympatric seabirds

**Abstract:**

Bird migration is commonly defined as a seasonal movement between breeding and wintering grounds. It is generally assumed to involve relatively straight and directed movement stretches, often with a latitudinal change, and characteristic daily activity patterns comprising less or no foraging and more traveling time. In addition, the spatial scale of movement is one order of magnitude larger during migratory stretches than during stationary periods. Here, our main objective was to test how well those statements apply to seabirds. Our first goal was to separate migratory stretches from stationary periods. Based on this characterization of the movements during the wintering period, our second goal was to compare the migration tactics between species and colonies. To this end, we used an extensive light-logger geolocator-based positional dataset on six pelagic seabird species (northern fulmar, common guillemot, Brünnich's guillemot, little auk, Atlantic puffin, black-legged kittiwake) from 29 colonies of the North-East Atlantic and several years, tracked as part of the SEATRACK project. Migratory stretches were identified based on track characteristics (movement rate, latitude, longitude). Additionally, we used the data obtained from conductivity sensors integrated to each light-logger to infer time spent flying, and when possible resting and foraging. During the non-breeding season, the six species had, on average, three to four migratory stretches and two to three distinct stationary periods. On average, tracked individuals spent the winter at lower latitudes than their breeding sites and followed specific migration routes rather than non-directionally dispersing from their colonies. Differences in daily activity patterns were small between migratory and stationary periods, suggesting that all species continued to forage and rest while migrating. Such a migratory strategy can be qualified as a "fly-and-forage". Our results show the importance of habitats visited during seabird migrations. Those habitats are not just flown over, but may be important for re-fuelling.

**Authors:**

Françoise Amélineau¹, Benjamin Merkel¹, Arnaud Tarroux², Sébastien Descamps¹, Tycho Anker-Nilssen², Oskar Bjørnstad³, Vegard Bråthen², Olivier Chastel⁴, Signe Christensen-Dalsgaard², Johannis Danielsen⁵, Francis Daunt⁶, Nina Dehnhard², Morten Ekker⁷, Kjell Einar Erikstad², Alexey Ezhov⁸, Per Fauchald², Maria Gavrilo⁹, Gunnar Hallgrímsson¹⁰, Erpur Hansen¹¹, Mike Harris¹², Morten Helberg¹³, Hálfdán Helgason¹⁴, Malin Johansen¹, Jon Jónsson¹⁵, Yann Kolbeinsson¹⁶, Yuri Krasnov⁸, Magdalene Langset², Svein-Håkon Lorentsen², Erlend Lorentzen¹, Mikhail Melnikov¹⁷, Børge Moe², Mark Newell¹², Bergur Olsen⁵, Tone Reiertsen², Geir Systad², Paul Thompson¹⁸, Thorkell Thorarinsson¹⁹, Ekaterina Tolmacheva²⁰, Sarah Wanless¹², Katarzyna Wojczulanis-Jakubas²¹, Jens Åström², Hallvard Strøm¹

¹Norwegian Polar Institute, ²Norwegian Institute for Nature Research, ³Karmøy Ringmerkingsgruppe, ⁴Centre d'Etudes Biologiques de Chizé. CNRS-Université de La Rochelle, ⁵Faroe Marine Research Institute, ⁶Centre for Ecology & Hydrology, ⁷Norwegian Environmental Agency, ⁸Murmansk Marine Biological Institute, ⁹National Park Russian Arctic/Association Maritime Heritage, ¹⁰Faculty of Life and Environmental Sciences, University of Iceland, ¹¹South Iceland Nature Centre, ¹²UK Centre for Ecology & Hydrology, ¹³University of Oslo, ¹⁴Náttúrustofa Austurlands, East Iceland Nature Research Centre, ¹⁵University of Iceland?s Research Centre at Snæfellsnes, ¹⁶Northeast Iceland Nature Research Centre, ¹⁷Lipetsk State Pedagogical University, ¹⁸University of Aberdeen, ¹⁹Northeast Iceland Nature Research Center, ²⁰Kandalaksha State Nature Reserve, ²¹University of Gdansk

How do seabird migrations differ from other bird migrations? An assessment on six pelagic species of the North Atlantic

**Abstract:**

The winter period is an energetic bottle neck for seabirds, challenging them with increased energy requirements due to higher thermoregulatory costs, diminished food resources, higher frequency of extreme weather events and shorter day lengths. These effects vary across latitudinal gradients of environmental severity. A critical question is therefore how individuals at higher latitudes in the breeding range obtain sufficient food to survive the winter. Specifically, it is unclear the extent to which individuals, a) migrate to lower latitudes to exploit longer day length, b) forage at night, or c) target higher quality food patches to minimise foraging time. We studied the migration and foraging strategies of European shags from six colonies across a latitudinal gradient spanning the Arctic Circle using geolocator/immersion loggers deployed over eight different winters. This species is a good candidate to test these questions since it has wettable plumage which results in high foraging costs during winter. We found that a proportion of individuals from higher-latitude populations remained resident in winter. In the absence of daylight they foraged during twilight and occasionally also during the night. The remainder of the population migrated south, benefiting from the longer photoperiod. At lower latitudes, there was little evidence that individuals migrated south and nocturnal feeding was absent, suggesting that there was sufficient daylight in winter. For no population was there evidence that foraging time was lowest in winter, which would suggest that prey availability changes less than expected. Thus, our results suggest responses to environmental conditions vary with latitude, and that individuals from higher latitudes may migrate south or increase crepuscular or nocturnal foraging. Our results demonstrate the range of individual strategies that enables a species to survive and breed across a marked latitudinal gradient.

**Authors:**

Børge Moe¹, Francis Daunt², Vegard Bråthen¹, Robert Barrett³, Manuel Ballesteros¹, Oskar Bjørnstad⁴, Nina Dehnhard¹, Kjell Einar Erikstad¹, Arne Follestad¹, Sindri Gíslason⁵, Gunnar Thor Hallgrímsson⁶, Svein-Håkon Lorentsen¹, Aevar Petersen⁷, Richard Phillips⁸, Sunna Ragnarsdóttir⁹, Tone Kristin Reiertsen¹, Sarah Wanless², Tycho Anker-Nilssen¹

¹Norwegian Institute for Nature Research, ²Centre for Ecology & Hydrology, ³UiT The Arctic University of Norway, ⁴Norsk Ornitologisk Forening, ⁵Southwest Iceland Nature Research Centre, ⁶University of Iceland, ⁷n/a, ⁸British Antarctic Survey, ⁹Icelandic Institute of Natural History

A mystery solved - How and where do guillemot chicks spend their second half of their rearing period?

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A mystery solved - How and where do guillemot chicks spend their second half of their rearing period?

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