United States

**Abstract:**

Seabirds are extensively used as environmental biomonitors and feathers are among the most analyzed matrices because they are one of the main excretory pathways to detoxify the bird&#39;s body of environmental contaminants. Still, there is a variation in contamination level between the different feathers of seabird species, driven by diet and physiology, such as molt strategy and feather formation sequence. We measured total mercury (THg) concentration in different types of feathers (wing, tail, ventral and dorsal) of the same individual in adults and juveniles of brown boobies (Sula leucogaster) from the northern coast of Rio de Janeiro state, Brazil. Brown booby adults and juveniles had higher THg concentration (µg.g-1 d.w.) in wing and ventral feathers compared to dorsal and tail feathers. This difference may be explained by the fact that feathers grow in a specific sequence during molts leading to different THg concentrations in each type of feather. Additionally, juveniles had significantly lower concentrations of THg than adults in all feather types, which may be explained by the shorter life span, leading to less time to bioaccumulate Hg in their body. It is essential to choose carefully which feather type is more suitable to be used as a biomonitor of THg contamination in a particular species. For brown boobies, we suggest the use of ventral feathers, which represent the highest Hg concentration, are easy to sample and do not impair the seabird&#39;s flight ability.

**Authors:**

Gabriel Bighetti¹, Janeide Padilha¹, Larissa Cunha¹, Olaf Malm¹, Patrícia Mancini¹

¹Federal University of Rio de Janeiro

3rd World Seabird Conference

Ventral feathers contained the highest mercury level in brown bobby (Sula leucogaster), a pantropical seabird species

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:**

Seabirds are extensively used as environmental biomonitors and feathers are among the most analyzed matrices because they are one of the main excretory pathways to detoxify the bird's body of environmental contaminants. Still, there is a variation in contamination level between the different feathers of seabird species, driven by diet and physiology, such as molt strategy and feather formation sequence. We measured total mercury (THg) concentration in different types of feathers (wing, tail, ventral and dorsal) of the same individual in adults and juveniles of brown boobies (Sula leucogaster) from the northern coast of Rio de Janeiro state, Brazil. Brown booby adults and juveniles had higher THg concentration (µg.g-1 d.w.) in wing and ventral feathers compared to dorsal and tail feathers. This difference may be explained by the fact that feathers grow in a specific sequence during molts leading to different THg concentrations in each type of feather. Additionally, juveniles had significantly lower concentrations of THg than adults in all feather types, which may be explained by the shorter life span, leading to less time to bioaccumulate Hg in their body. It is essential to choose carefully which feather type is more suitable to be used as a biomonitor of THg contamination in a particular species. For brown boobies, we suggest the use of ventral feathers, which represent the highest Hg concentration, are easy to sample and do not impair the seabird's flight ability.

**Authors:**

Gabriel Bighetti¹, Janeide Padilha¹, Larissa Cunha¹, Olaf Malm¹, Patrícia Mancini¹

¹Federal University of Rio de Janeiro

poster

**Abstract:**

The marine environment is changing rapidly due to climate change and increasing anthropogenic activities. Understanding how the usage of spatial habitat by seabirds and their prey species may change with both of these pressures is essential for the predictions of population trends and current decision making on sustainable spatial management. Where both predator and prey species are highly mobile, it is important to predict how well their preferred habitats continue to overlap in future scenarios. The diversity of individually preferred habitat variables and drivers of those habitats may all be changing quite differently under the different pressures of climate change and anthropogenic activities. To predict future seabird-prey spatial habitat overlap we will present two synergistic approaches. The first is a spatial statistical Bayesian hierarchical approach called Joint Modelling with INLA (integrated Nested Laplace Approximation). Joint Modelling, as compared to typical single-species spatial distribution modelling, allows both predator and prey as a response variable, creating an output called a 'common spatial trend' that allows quantification of overlap in future predator-prey distributions using a 'business as usual' climate model for 2050. The degree of change within common spatial trends is presented between contrasting seabirds: common guillemot, black-legged kittiwake, northern gannet and two prey species: herring, sandeels. The second is a time series approach using a Bayesian Network Ecosystem Model with a range of species across all trophic levels from 1990-2014. Within both approaches, we have used the same six important bio/physical variables (2 types of primary production, stratification, temperature, vertical and horizontal speed). The outcomes presented include the startlingly amount of change in common spatial trend predicted in just 30 years and the degree to which bottom-up forces are predicted as the drivers for population change.

**Authors:**

Beth Scott¹, Neda Trifonova¹, Dinara Sadydova², Alexander Sadykov³, Michela De Dominicis⁴, Sarah Walkin⁴, Judith Wolf⁴

¹University of Aberdeen, ²University of Queen's Belfast, ³University of Queen's Belfast, ⁴National Oceanographic Centre

Spatial and temporal Bayesian approaches to predict future seabird-prey overlap and population change

**Abstract:**

Mandt's Black Guillemot (Cepphus grylle mandtii) is one of the few Arctic seabirds dependent on sea ice and associated waters throughout the year. This species has undergone a long-term decline since the early 1990s, coinciding with a shift in the Arctic Oscillation causing increased atmospheric temperatures and sea ice melt throughout the Arctic. The largest breeding colony of the species in the Beaufort Sea, at Cooper Island, has been monitored annually since 1975. At its most prolific time, in 1987, the colony supported 209 breeding pairs, while in 2019 only 80 pairs bred. Past studies showed that climatic and oceanographic changes are linked to the observed decline: breeding productivity of this colony has decreased as decreasing summer sea ice reduced prey availability to parents provisioning nestlings. However, a full understanding of the demographic response of the colony to the recent environmental changes in the region requires to study its whole population dynamic. To fulfill this aim, we are analyzing a 45-year database with detailed information on the breeding and survival of 5456 individuals with known histories. Results indicate a high sensitivity of the population growth to immigration and experienced breeder survival. We found a decrease in immigration to be the most important factor in the colony's decline, with a positive correlation between summer sea ice concentration at source colonies and subsequent immigration rate on Cooper Island. We are currently expanding the model to include environmental covariates and quantify their respective influence on the demographic parameters, and preliminary results already suggest that survival of black guillemots is positively correlated with sea ice extent in winter foraging area. Our long-term monitoring data and model provide one of the few biological evidence of the consequences of recent sea ice loss to Arctic bird populations and Artic biota in general.

**Authors:**

Pierre-Loup Jan¹, Christophe Barbraud¹, Stéphanie Jenouvrier², George Divoky³

¹French National Centre for Scientific Research, ²Woods Hole Oceanographic Institution, ³Friends of Cooper Island

How sea ice processes and climate fluctuations affect the demography an Arctic diving seabird?

**Abstract:**

Emperor penguins are iconic examples of a species threatened by future climate change. Projections indicate that most breeding colonies will be endangered by 2100 under "business as usual" emissions scenarios, resulting in dramatic declines in the global population size even under optimistic dispersal scenarios. These declines occur through projected loss of Antarctic sea ice, to which the Emperor penguin life cycle is closely tied. Emperor penguins directly rely on seasonally stable sea ice as a breeding platform during the Antarctic winter and throughout the spring chick-rearing period. During the non-breeding season, sea ice serves as a platform from which they feed, molt, and seek refuge from predators. The Paris Agreement is a multinational initiative to combat climate change by keeping a global temperature increase in this century to 2C above pre-industrial levels while pursuing efforts to limit the increase to 1.5C. Here, we project the dynamics of all known Emperor penguin colonies under new climate change scenarios meeting the Paris agreement objectives using a climate--dependent--metapopulation model. Under business--as--usual greenhouse gas emissions, large sea ice loss are projected by 2100. As a result, 80% of the colonies are projected to be quasi-extinct by 2100, thus the total abundance of Emperor penguins is projected to decline by at least 81% relative to its initial size, regardless of dispersal abilities. In contrast, if the Paris Agreement objectives are met, viable Emperor penguin refuges will exist in Antarctica because sea ice loss are projected to be much less severe. Only 19% and 31% colonies are projected to be quasi-extinct by 2100 under the Paris 1.5 and 2 climate scenarios respectively. As a result, the global population is projected to decline by at least by 31% under Paris 1.5 and 44% under Paris 2. However, population growth rates stabilize in 2060 such that the global population will be only declining at 0.07% under Paris 1.5 and 0.34% under Paris 2, thereby halting the global population decline. Hence, global climate policy has a larger capacity to safeguard the future of Emperor penguins than their intrinsic dispersal abilities.

**Authors:**

Hoilland Marika¹, David Iles², Sara Labrousse², Laura Landrum¹, Jimmy Garnier³, Hal Caswell², Henri Weimerskirch⁴, Michelle La Rue⁵, Rubao Ji², Christophe Barbraud⁴

¹NCAR, ²WHOI, ³University Savoie Mont-Blanc, ⁴CEBC/CNRS, ⁵University of Canterbury

Climate mitigation halts penguin extinction due to projected sea ice loss.

**Abstract:**

The shelf ecosystems of the Pacific Arctic support millions of migratory seabirds during the summer and fall. Sea ice loss may pose a nutritional challenge to planktivorous seabirds that rely on lipid-rich zooplankton during reproduction. Conversely, delayed sea ice formation in the fall may provide access to ice-free habitat and improve post-breeding foraging conditions. We investigated the response of planktivorous auklets (crested, Aethia cristatella and least, A. pusilla) to variable winter sea ice conditions in 2015-2019. First, we examined whether auklet's exposure to nutritional stress during the breeding season is associated with their diet composition and reproductive performance on St. Lawrence Is., Alaska. In the summers of 2018 and 2019, after historic low winter sea ice formation, both crested and least auklet adults experienced severe food shortages, indicated by high concentrations of corticosterone in blood and feather tissues. Ongoing analysis of diets and isotopic niches will elucidate whether these responses were widely spread and accompanied by drastic changes in prey. Second, we used geolocators to track individuals during the post-breeding period of 2016-2017 (relatively early sea ice formation) and 2017-2018 (late sea ice formation) and found that the timing of sea ice formation in the fall did not determine when auklets departed the Arctic; departure was consistent across years and likely linked to disappearance of prey. In all years, feather corticosterone levels were higher during late winter than during the summer, and molecular damage (as reflected in telomere loss) accrued by crested auklets was higher during winters with historic low sea ice formation. Higher levels of nutritional stress and accrued molecular damage on the breeding and wintering grounds suggest that sea ice loss is currently a threat rather than an opportunity to migratory planktivores in the Pacific Arctic.

**Authors:**

Alexis Will¹, Jean-Baptiste Thiebot², Akinori Takahashi², Elena Golubova³, Alexei Pinchuk¹, Alexander Kitaysky¹

¹University of Alaska Fairbanks, ²National Institute of Polar Research, ³Russian Academy of Sciences

Sea ice loss and planktivorous migratory Arctic seabirds: challenge or opportunity?

**Abstract:**

Overall, sea ice extent is declining in Arctic systems. However, variability in inter-annual sea ice extent is increasing. Sea ice dynamics greatly influence trophic dynamics in marine systems, where changes in sea ice extent and timing of ice melt can affect the abundance and distribution of fish and invertebrate species. Higher trophic level Arctic breeding species, such as thick-billed murres (Uria lomvia), could be negatively affected by changes in sea ice extent via impacts on foraging behaviour, resulting in greater foraging effort in low ice years. Colony size has also been shown to influence foraging behaviour, where individuals at larger colonies must forage at greater distances as resources surrounding the colony are depleted at a faster rate (Storer-Ashmole's halo hypothesis). As such, the impacts of ice extent on foraging effort are likely to have colony-specific impacts on the energetic profitability of foraging and therefore breeding success. To quantify the impact of changing environmental conditions on the foraging behaviour and payoffs of murres at different sized colonies we deployed GPS units and GPS accelerometers at two colonies in the low Arctic, Coats Island, Nunavut (30 000 breeding pairs; sampled in 2018, and 2019) and Digges Island, Nunavut (400 000 breeding pairs; sampled in 2014, 2015, and 2016). We measured sea ice extent throughout the breeding period and collected blood samples before and after GPS deployments to measure energetic hormones (corticosterone) and energetic metabolites (non-esterified fatty acids, beta-hydroxybutyrate, and triglycerides) as proxies for foraging success of trips. Quantifying the complex impacts of the interaction between colony size and ice extent on foraging success and foraging flexibility will give us predictive insight into which breeding colonies may have a greater capacity of withstanding Arctic climate change.

**Authors:**

Alyssa Eby¹, Allison Patterson², Graham Sorenson¹, Thomas Lazarus², Kyle Elliott², H. Grant Gilchrist³, Oliver Love¹

¹University of Windsor, ²McGill University, ³Environment and Climate Change Canada

Comparing foraging success of thick-billed murres (Uria lomvia) from two colonies in the Canadian Arctic in response to environmental conditions

**Abstract:**

Social Attraction has become an important tool for seabird conservation worldwide. Pioneered in 1977 in Maine, USA, this method uses the sights and sounds of thriving seabird colonies to attract birds to quality habitat. Since the success of puffin and tern restoration in Maine, over 47 species have been lured to more than 116 favorable sites in 14 countries. Multiple species from the families Spheniscidae, Diomedeidae, Procellariidae, Hydrobatidae, Pelecanoididae, Sulidae, Phalacrocoraciidae, Laridae, and Alcidae, have responded to decoys, mirrors, sounds, and other social cues to nest in safe places. Decoys are made from a variety of materials including wood, plastic, concrete, and fiberglass, with various degrees of realism. Auditory cues have most often been provided by solar-recharged sound systems which play 24/7, nocturnally, or at prescribed intervals throughout the breeding season. Two formerly distinct, but now aligned, conservation-minded enterprises have emerged to supply materials for social attraction projects around the world. Mad River Decoys (now Mad River Decoy by Audubon-MRDA) and Murremaid Music Boxes (MMB) have provided equipment for projects targeting 35 species in 10 countries (18 states and 4 territories in USA). New MRDA and MMB efforts include roto-molded decoys manufactured from 100% recycled plastic, remotely controlled sound system activation/deactivation, and remote auditory and visual monitoring of restoration efforts.

**Authors:**

Susan Schubel¹, Stephen Kress¹, Donald Lyons¹

¹Audubon Seabird Restoration Program

A summary of seabird social attraction projects utilizing Mad River Decoys and Murremaid Music Boxes

**Abstract:**

Wildlife tourism is increasing all over the world, and its effects may be detrimental to the species involved. Negative effects of human visitation on seabirds may be worse at particularly stressful life stages such as breeding. The current study took place at Martillo Island, Argentina, where approximately 4000 pairs of Magellanic penguins (Spheniscus magellanicus) breed every year. Two groups were defined: individuals nesting within 20 meters of the tourist trail (n=27) and individuals not breeding within sight of the tourists (n=54). Breeding adults were sampled during egg incubation (September/October 2017, n=31) and chick rearing in two distinct years with (2017) and without tourism visitation in 2020 due to the global pandemic (December 2017/January 2017 and January 2020, n=50). A drop of blood was extracted from the tarsal vein and blood smears were made. Smears were fixed with alcohol 70% and dyed with Giemsa stain. Leucocyte types (lymphocytes, heterophils, eosinophils, basophils and neutrophils) were identified under optical microscope at x1000. Percentage of each cell type was estimated as well as the eosinophil/lymphocyte (E/L) and heterophil/lymphocyte (H/L) ratio as a proxy of immune response to parasites and long-term stress, respectively. For 2017, GLMs were generated with factor (tourism vs. no tourism) and stage (incubation or chick rearing) as fixed effects. Tourism had an effect on all values: higher percentage of heterophils (t=3.18, p<0.05), eosinophils (t=2.76, p<0.05) and heterophil/lymphocyte (t=4.22, p<0.05) and eosinophil/lymphocyte ratios (t=3.45, p<0.05) and lower lymphocyte counts (t= 4.12, p<0.05) than in areas not visited by tourists with no differences between stages (incubation or chick rearing). In 2020, however, there were no differences in physiological parameters between birds nesting in areas usually visited vs. not visited by tourists (percentage of heterophils (t=0.96, p=0.34), eosinophils (t=1.00, p=0.32) and lymphocyte counts (t= 0.87, p=0.39), and H/L (t=0.56, p=0.58) and E/L ratios (t=1.07, p=0.29). These results are preliminary as a larger sample is needed over a more extended period of time. However, there seem to be differences in physiological parameters of individuals exposed or not tourism and these effects are reverted once tourism does not occur. In view of these results, questions rise as to the consequences of growing tourism on the Magellanic penguin colony at Martillo Island.

**Authors:**

Sabrina Harris¹, Gabriela Scioscia¹, Andrea Raya Rey¹

¹CADIC-CONICET

Tourism at Martillo Island, Tierra del Fuego (Argentina): are Magellanic penguins (Spheniscus magellanicus) feeling it?

**Abstract:**

Wilson's storm-petrels (Oceanites oceanicus) are the smallest seabirds breeding in Antarctica, where events like snowstorms often prevent parents from providing food daily for their offspring. To survive such times of limited food supply Wilson's storm-petrel chicks can minimize their energy expenses by heterothermy: reducing their metabolism and body temperature. As heterothermy is reported to impact development, time spent hypotherm could have negative impacts for their future lives. A proposed consequence is that chicks are forced to fledge in poorer body conditions because of decreased time for development. Here we show the first results of our study of heterothermy and its consequences in a breeding colony of Wilson's storm-petrels at King George Island, Antarctic Peninsula. We investigated the impact of hypothermia on different parameters concerning chick development like blood fat values, immunology, telomere shortening, and growth. Triglyceride plasma values fell with increasing time spent at colder body temperatures within the last days before sampling. However, immune response to a phytohaemagglutinin test were not different in chicks that experienced more frequent hypothermic events than those that always maintained a constant body temperature. As snowfall is predicted to increase on the Antarctic Peninsula due to climate change, the use of heterothermy may ensure chick survival during continuous events of food limitation. The impact of heterothermy on their development and survival may hence become of high importance on the long term for the well-being of colonies breeding in this area.

**Authors:**

Nadja Kuepper¹, Christina Bauch², Gábor Czirják³, Marcela Libertelli⁴, Petra Quillfeldt¹

¹Justus Liebig University of Giessen, ²University of Groningen, ³Leibniz Institute for Zoo and Wildlife Research, ⁴Instituto Antártico Argentino

Physiological and developmental impacts of heterothermy on Wilson's storm-petrel chicks

**Abstract:**

Mercury (Hg) is a widely available pollutant in the world's oceans. Its distribution is far from homogenous showing vertical stratification in the water column as well as spatial heterogeneity within and among ocean basins. In the Southern Ocean, penguins are considered effective indicators of Hg in the marine food web because of their relatively high trophic level, vagility combined with discrete and rather accessible reproductive grounds and their unusual feather molting pattern allowing for specific time-integrated sampling. Previous studies have shown elevated Hg concentrations in the South Western Atlantic Ocean. To provide further insights on regional variation in Hg prevalence within this basin we measured Hg concentration and carbon and nitrogen stable isotope composition in feathers of southern rockhopper penguins (Eudyptes chrysocome). Rockhopper penguins present population genetic structure in this area and different foraging areas for each genetic cluster. The northern genetic cluster forages at a higher trophic position, but yielded a two- to three-fold lower Hg concentration than the southern one. Interestingly, all adults from the southern cluster exceed the feather toxicity threshold of 5 μg/g. Previous studies also show that the Northern Patagonian Shelf presents lower concentrations compared to southernmost South America, which implies a recurring pattern rather than a particularity. This implies a different vulnerability due to the exposure to Hg for each cluster, but especially for predators feeding on rockhoppers, i.e. marine top predators, gulls and caracaras. Southern colonies could therefore serve as a model to investigate adverse effects of Hg contamination on penguins and downstream in their food webs.

**Authors:**

Nicolas Lois¹, Ulises Balza², Samanta Dodino², Michael Polito³, Klemens Pütz⁴, Rebecka Brasso⁵, Andrea Raya Rey²

¹Universidad de Buenos Aires, ²CONICET - Centro Austral de Investigaciones Cientificas, ³Louisiana State University, ⁴Antarctic Research Trust, ⁵Weber State University

Foraging area rather than trophic level explains mercury concentration in Patagonian rockhopper penguin colonies

**Abstract:**

Mercury (Hg) is a pervasive environmental pollutant that affects seabirds´ physiology with short- and long-term fitness consequences. Brown Skuas (Stercorarius antarcticus) are opportunistic top predators and scavengers, and therefore are effective bioindicators of contamination. We measured total mercury (THg) concentration and the stable isotopes of carbon (δ13C, a proxy of feeding habitat) and nitrogen (δ15N, a proxy of trophic position/diet) in blood from breeding adult Brown Skuas at Esperanza/Hope Bay (Antarctic Peninsula) (N=49). The aim of the study was to evaluate the influence of individual traits (body condition and sex) and foraging ecology (δ13C and δ15N values) on Hg exposure, and to determine the relationship between THg concentration with body condition and breeding success. We fitted general linear models, and the most parsimonious model included sex, sampling date, breeding season, body condition and δ15N as variables. Mean ± SD THg concentration in blood was 0.82±0.36 µg g-1dw, and was higher in males (N=25, 0.89±0.38 µg g-1dw) than in females (N=24, 0.75±0.33 µg g-1dw). Adults with higher THg showed lower body condition, and in females, also lower breeding success. In addition, a positive association was observed between THg concentration and δ15N reflecting bioaccumulation from prey. Males showed higher THg loads than females, probably because females can deposit Hg in eggs, which may explain why females with higher THg were less likely to fledge chicks. Together, these results indicate that Hg has deleterious effects on reproduction in adult skuas, with potential long-term repercussions at the population level.

**Authors:**

Andrés Ibañez¹, William Mills², Paco Bustamante³, Lara Morales⁴, Diego Torres⁴, Facundo Palacio⁴, Nadia Haidr¹, Rocío Mariano-Jelicich⁵, Richard Phillips⁶, Diego Montalti⁴

¹La Plata Museum, ²University of Exeter/British Antarctic Survey, ³CNRS-La Rochelle Université, ⁴La Plata Museum (FCNyM-UNLP), ⁵UNMdP-CONICET, Universidad Nacional de Mar del Plata, ⁶Cambridge University

Ventral feathers contained the highest mercury level in brown bobby (Sula leucogaster), a pantropical seabird species

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