United States

**Abstract:**

The migratory behaviour of the Yelkouan Shearwater, a seabird endemic to the Mediterranean Sea and classified &#39;Vulnerable&#39; according to IUCN criteria, remains poorly understood to date. While Yelkouans of various Mediterranean origins (Malta, France, Greece) have been sighted occasionally from summer to autumn as far as the Black Sea, others have been observed in the southern Mediterranean waters. Here we describe for the first time the post-breeding journeys of 11 adults from a colony in Lastovo Archipelago, central Adriatic (Croatia) which we equipped in late June 2021 with ultra-light GPS-GSM loggers that are still active at the time of this writing. The results display a strong variability in the journeys of individuals from the same nesting site. In the space of only six weeks, three adults had already traveled over 2500 km, following the same route although days apart, to reach the pelagic waters of the Black Sea. At least one of them was tracked all the way till the entrance of the Azov Sea - a major spawning ground for anchovies. Others stopped their journey - for weeks at least - in islands of the Aegean Sea, home to many yelkouan nesting colonies. Other individuals kept foraging between the Italian and Croatian coasts of the Adriatic Sea, while others limited their flights to the vicinity of their nests in the Lastovo archipelago. Our preliminary conclusions underline the similarity of the long, rather precise, migratory route followed by the yelkouans to reach the Black Sea. Our study raises many further questions: to begin with, what is the precise stimulus that triggered the start of their respective migration?

**Authors:**

Loriane MENDEZ¹, Sven Kapelj², Paula Moschella¹, Frederic Briand¹

¹CIESM (Mediterranean Science Commission), ²Association BIOM

3rd World Seabird Conference

The summer migration of the Yelkouan Shearwater (Puffinus yelkouan) from a single island in Croatia

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:**

The migratory behaviour of the Yelkouan Shearwater, a seabird endemic to the Mediterranean Sea and classified 'Vulnerable' according to IUCN criteria, remains poorly understood to date. While Yelkouans of various Mediterranean origins (Malta, France, Greece) have been sighted occasionally from summer to autumn as far as the Black Sea, others have been observed in the southern Mediterranean waters. Here we describe for the first time the post-breeding journeys of 11 adults from a colony in Lastovo Archipelago, central Adriatic (Croatia) which we equipped in late June 2021 with ultra-light GPS-GSM loggers that are still active at the time of this writing. The results display a strong variability in the journeys of individuals from the same nesting site. In the space of only six weeks, three adults had already traveled over 2500 km, following the same route although days apart, to reach the pelagic waters of the Black Sea. At least one of them was tracked all the way till the entrance of the Azov Sea - a major spawning ground for anchovies. Others stopped their journey - for weeks at least - in islands of the Aegean Sea, home to many yelkouan nesting colonies. Other individuals kept foraging between the Italian and Croatian coasts of the Adriatic Sea, while others limited their flights to the vicinity of their nests in the Lastovo archipelago. Our preliminary conclusions underline the similarity of the long, rather precise, migratory route followed by the yelkouans to reach the Black Sea. Our study raises many further questions: to begin with, what is the precise stimulus that triggered the start of their respective migration?

**Authors:**

Loriane MENDEZ¹, Sven Kapelj², Paula Moschella¹, Frederic Briand¹

¹CIESM (Mediterranean Science Commission), ²Association BIOM

poster

**Abstract:**

Ingestion of plastic by marine fauna has been reported all around the world and affects a large number of seabirds including albatrosses, petrels, shearwaters, seagulls and boobies. Most of the studies on plastic ingestion by seabirds realized so far have been focusing in the Pacific and Atlantic Oceans but no information has been published on this issue in the western Indian Ocean. In this study we investigated plastic ingestion in nine seabird species breeding or foraging at Reunion Island and at Juan de Nova (Mozambique Channel), among which two species are endemic and endangered (the Barau's Petrel, Pterodroma baraui) or critically endangered (the Mascarene petrel, Pseudobulweria aterrima). We analyzed the stomach contents of 222 individuals and showed the most affected species are tropical shearwaters (79%) and Barau's petrels (59%). The average number of plastic particles per contaminated bird was higher in Barau's petrels (6.10 ± 1.29) than in tropical shearwaters (3.84 ± 0.59) and all other studied species also showed plastic presence in their stomach contents to a lesser extent. We analyzed differences in plastic ingestion between juveniles and adults for three different species: Barau's petrels, tropical shearwaters and white-tailed tropicbirds. We showed significantly more plastic particles in juveniles of Barau's petrels than in adults and a significantly higher mass of plastic particles both in juveniles Barau's petrels and tropical shearwaters than in adults of these two species. These results demonstrate that the foraging areas of seabirds of the western Indian Ocean have a high level of plastic pollution. In Reunion Island, hundreds of tropical shearwaters and Barau's petrels are attracted by urban lights and die each year so we suggest to take advantage of this situation by using these species as long-term indicators of plastic marine pollution in the region. Keywords: plastic ingestion, seabird, marine pollution, Indian Ocean, Pterodroma baraui, Puffinus bailloni.

**Authors:**

Audrey Cartraud¹, Matthieu Le Corre¹, Jean Turquet¹, Julie Tourmetz¹

¹Université de La Réunion

Plastic ingestion in seabirds of the western Indian Ocean

**Abstract:**

The Northern Gannet Morus bossanus is an avian sentinel; the largest breeding seabird in Ireland and an obligate piscivore. Gannet eggs were collected from two island colonies off the east coast of Ireland, approximately 150km from each other, in locations with divergent history of industrialization (n = 10-20). Levels of potentially harmful contaminants including Polychlorinated biphenyls (PCBs), Polybrominated diphenyl ethers (PBDEs), Organochlorine pesticides (OCs), heavy metals and mercury were measured and differences of contaminant concentrations between different colonies compared. This is the first such study of contaminant levels in Gannet, or in any seabird egg in Ireland. Stable isotopes of carbon (d13C) and nitrogen (d15N) were measured in each egg to understand the influence of diet in contaminant levels detected. Significantly higher levels of PCBs, PBDEs and mercury were detected near Dublin (Ireland's industrialized capital city and location of its largest port) compared to Wexford. No differences were observed in levels of OCs and heavy metals between the two colonies. Stable isotope analysis demonstrated that Gannets in both locations occupy the same dietary niche excluding a difference in diet as the driver of differing contaminant levels in the two feeding areas. Though Gannets travel significant distances when foraging for food (~200km) tracking studies have shown that Gannets colonies maintain exclusive feeding areas with little overlap between neighbouring colonies. Differences between colonies within the feeding range of Gannets can therefore be detected despite Gannet's high dispersal ability. These results are in concurrence with elevated levels of contaminants in lower trophic level organisms that have been found in Dublin Bay compared to the rest of Ireland, indicating potential for Gannets as a higher trophic level indicator - though variability in their diet, including feeding on fishing discard, may lead to unacceptable levels of variability for an indicator species.

**Authors:**

Andrew Power¹, Philip White¹, Brendan McHugh², Sinead Murphy¹, Simon Berrow¹, Moira Schlingermann¹, Stephen Newton³, Linda O'Hea², Brian Boyle², Marissa Tannian², Denis Crowley², Evin McGovern², Ian O'Connor¹

¹Galway Mayo Institute of Technology, ²Marine Institute, ³BirdWatch Ireland

Persistent organic pollutants and heavy metal concentrations in Northen Gannet (Morus bossanus) eggs in two island colonies in Ireland

**Abstract:**

While the problem of plastic pollution in the oceans has received wide media and public attention in the last decade, the scientific basis for our knowledge of its effects and consequences is still limited, despite meeting the irreversibility and global ubiquity criteria of being a planetary boundary threat. Since 2005, the Adrift Lab has studied the impact of plastics pollution on shearwaters (Ardenna spp) in Australia with an aim to understand the nature, extent, and consequences of plastics for the birds and their island ecosystems. We have employed a variety of tools, including contaminant analysis, nutritional biochemistry, histology, and blood chemistry combined with annual surveys of the frequency and intensity of plastic pollution, focusing on Flesh-footed Shearwaters (Ardenna carneipes) on Lord Howe Island. Here, we review the progress in knowledge around how plastics may be affecting individuals, populations, and communities. Birds with more plastics tend to have slower growth rates, higher contaminant burdens, altered physiology, and show tissue damage to the gastrointestinal tract compared with less-affected individuals. Birds also transport considerable volumes of plastic to the island and deposit it through regurgitation, and decomposition of carcasses. As one of the longest-running plastics monitoring research programmes in the world, we are able demonstrate the annual variability in plastic ingestion, and leverage this knowledge to begin to explore the broader effects of plastics on marine wildlife.

**Authors:**

Alexander Bond¹, Jennifer Lavers², Ian Hutton³

¹Natural History Museum, ²University of Tasmania, ³Lord Howe Island Museum

The shearwater and the bottlecap: understanding the broader impacts of plastic ingestion on seabirds

**Abstract:**

Plastic circulates at sea threatening marine megafauna. Southern Giant Petrels (SGP, Macronectes giganteus) are known to consume plastic, but the source and accumulation areas of marine litter remain unknown. The goal of this study is to understand how foraging behavior of SGP will impact their risk of plastic ingestion by mimicking the circulation of floating debris. We tracked 34 adult and juvenile birds using either PTTs or GPS, from Arce (45°00'S; 65°29'W) and Gran Robredo Islands (45°80'S; 66°03'W). To mimic plastic circulation at sea we employed the output of 15 years of daily-forcing simulations using ROMS-Agrif. We designed lagrangian simulations of particles (individual based model) using off-line particle-tracking model. Simulations incorporate physical characteristics of plastic that reaches the area from coastal cities and ships. Dual foraging strategy was recorded for all breeding birds. During short trips (N=108, recorded with GPS), both sexes foraged at 38.5 ± 12.9 km from the colony. During long trips (N= 60), males mainly foraged along the coast at 382 ± 65 km from the colony, while females moved to the shelf break and the middle shelf (459 ± 58 km). Throughout austral fall and winter, adults remained on the Patagonian shelf, but juveniles moved north using the shelf break as a corridor. The drift model showed how simulated particles generated a plastic corridor along the Patagonian shelf until reaching the Malvinas-Brazil confluence, concurring with juveniles' migration path. Accumulation hot spots occurred in the mid shelf and along the shelf break with a strong seasonal variation, overlapping with breeding females. Litter coming from cities and fisheries accumulated near the colony, corresponding with adult foraging areas during short trips, which may explain the 50 to 73% of plastic items found in chicks' diet. Our results showed that marine litter dispersed by ocean circulation, will threat SGP, depending on sex, age class, and breeding stage. Understanding where marine organisms come into contact with plastic, could help elucidate negative effects at population-levels to design management strategies that mitigate this environmental issue.

**Authors:**

Gabriela Blanco¹, Mariano Tonini², Gallo Luciana¹, Flavio Quintana¹

¹Instituto de Biologia de Organismos Marinos - CONICET, ²Instituto Andino Patagonico de Tecnologias Biologicas y Geoambientales - CONICET

Sex, age class, and foraging strategy of the Southern Giant Petrel might influence the hazard of plastic ingestion on the Patagonian shelf

**Abstract:**

Through a collaborative network, we evaluated plastic ingestion (items >1 mm) in 16 Procellariiform species along the coast of Brazil and Argentina. Plastic items were found in 30.2% of carcasses examined (n=161), with White-chinned Petrel (Procellaria aequinoctialis), Southern Giant Petrel (Macronectes giganteus) Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos), and Manx Shearwater (Pufinus puffinus) being the most susceptible species. Our results showed a high frequency of occurrence (FO) of plastic ingestion in birds bycaught offshore in southern Brazil (FO=42.8%, n=21) but not in birds bycaught offshore in southern Argentina (FO=0%, n=46). Plastic ingestion was frequently recorded in beach-wrecked carcasses, being highest in Chubut, Argentina (FO=100%, n=3), followed by Espírito Santo, Brazil (FO=61%, n=23), Santa Catarina, Brazil (FO=23%, n=13), and Buenos Aires, Argentina (FO=20%, n=5). In birds that died at rehabilitation facilities, plastic ingestion was similarly frequent in Espírito Santo (FO=27%, n=11) and Santa Catarina (FO=29%, n=14). A high FO of plastic ingestion was also noted in Southern Giant Petrel carcasses collected at breeding colonies in Chubut, Argentina (FO=54%, n=24). The most common plastic items found in the bird's gut were fragments (71% of recovered items; including film and rigid fragments), followed by foam (i.e. polystyrene/polyurethane; 12%), pellets (10%), nylon line (4%) and other types of plastic (3%). Our findings confirm that plastic ingestion is a common problem for Procellariiforms in the Southwest Atlantic Ocean and highlight the need for mitigation and at-source reduction. The use of standardized protocols for sample collection and analysis along with comparable metrics and terminology will allow comparisons between investigations, as well as the detection of large-scale spatiotemporal patterns.

**Authors:**

Luciana Gallo¹, Patricia Pereira Serafini², Ralph E. T. Vanstreels³, Tamini Leandro⁴, Cristiane Kolesnikovas⁵, Alice Pereira⁶, Tatiana Neves⁶, Gabriel Nascimento², Anabella Gerez⁷, Nahuel Chavez⁴, Ruben DellaCasa⁴, Marcela Uhart⁸

¹IBIOMAR-CONICET, ²CEMAVE / ICMBio / MMA, ³Instituto de Pesquisa e Reabilitação de Animais Marinho, ⁴Albatross Task Force, Aves Argentinas/AOP y BirdLife International, ⁵R3 Animal, ⁶Projeto Albatroz, ⁷Universidad Nacional de la Patagonia San Juan Bosco, ⁸One Health Institute, School of Veterinary Medicine, University of California

Plastic ingestion in albatrosses and petrels off the shores of Argentina and Brazil

**Abstract:**

Ingestion of marine debris by seabirds is widespread. Procellariiformes is the group with the highest frequency of ingestion, and the most threatened group of all birds. Here, we report the prevalence of type, color, size and weight of ingested debris by these species in southern Brazil, and short-term trends of ingestion along nine years of survey (2007 - 2015). We analyzed 767 stomachs from 18 species of beached-washed seabirds, and found the highest prevalence, abundance and mass of debris in Great shearwaters (GS), with almost 91% of individuals containing debris in their stomachs, and a mean of 22.6 ± 30.5 fragments weighting 0.44 ± 0.72g. The Manx shearwater (MS), Cory's shearwater (CS) and White-Chinned petrel (WCP) showed intermediate prevalence (63.4%, 54.2% and 47.8%, respectively), while the Yellow-nosed and Black-browed albatrosses showed low prevalence (9.3% and 10.5%). The number of items per individual ranged from 1-261 for CS, 1-174 for GS, 1-108 for the MS and 1-65 for WCP. Hard plastic fragments had the highest prevalence (Pr) in shearwaters (Pr = 65-85%), while sheet plastics were most frequent in albatrosses (62%). Threadlike plastic, i.e. nylon threads, were most frequent in WCP (45%). Pellets were found only in stomachs of WCP and shearwaters, and we found the highest prevalence in GS (50%). The most frequently ingested size category was microplastics (<5mm), followed by mesoplastics (5-20 mm). Off/white-clear plastics were the most abundant and frequently ingested color by all species. We found a decreasing trend in prevalence of debris ingestion for CS (R² = 0.75, p < 0.01) and MS (R² = 0.57, p = 0.02), both northern hemisphere breeders, while GS and WCP, both southern hemisphere breeders, showed a steady prevalence (R² = 0.27, p = 0.14, and R² = 0.04, p = 0.59, respectively). Northern migrants also ingested, on average, smaller masses of debris than southern migrants did (U = 9070, p < 0.01). Our results show that northern migrants are ingesting less plastic than southern breeders, in both frequency and mass. This may be related to European policies for plastics reduction, which have intensified over the past decade.

**Authors:**

Júlia Grohmann Finger¹, Victória Fontoura Benemann¹, Maria Petry¹

¹Universidade do Vale do Rio dos Sinos

Marine debris ingestion by tube-nosed seabirds off Southern Brazil: are northern migrants winning the race against plastic pollution?

**Abstract:**

Plastic pollution ingestion by seabirds is an increasing environmental problem even in remote areas such as the Arctic, yet knowledge on plastic pollution ingestion by several Arctic seabirds is limited, making it difficult to assess trends. We examined plastic pollution ingestion by northern fulmars (Fulmarus glacialis), black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia) and black guillemots (Cepphus grylle) in the Canadian Arctic to assess species-specific and temporal differences in plastic ingestion over ten years. Seventy-two percent of fulmars and 15% of kittiwakes ingested plastic, while guillemots and murres did not. The number and mass of plastic ingested by fulmars decreased between the two periods (2008 and 2018), but the frequency of occurrence of plastic ingestion did not change, although sample sizes were less than ideal. Future research with larger samples is recommended to reinforce these trends in plastic ingestion by Arctic seabirds.

**Authors:**

Julia Baak¹, Jennifer Provencher², Mark Mallory³

¹McGill University, ²Environment and Climate Change Canada, ³Acadia University

Plastic ingestion by four seabird species in the Canadian Arctic: Comparisons across species and time

**Abstract:**

Plastic presence in the world's oceans has increased dramatically over the past few years, becoming a threat to marine wildlife especially top predators such as seabirds. Therefore, it is crucial to monitor plastic levels in the marine environment to understand its impacts, not only on threatened species but also on other species. Our study evaluates plastic ingestion in guanay cormorants (Phalacrocorax bougainvillii) through pellet analysis at ten colonies along the Peruvian coast between 2018 and 2019. A total of 2,286 pellets were collected and analyzed, of which plastic debris was present in 162 (10.8%) pellets (N = 1497) consisting of mainly user plastics and varying in size from mega (>20 mm) to micro (1-5 mm) plastics (nano plastics were not assessed). Micro and meso plastic (5-20 mm) were most abundant with 67% and 23% by number, respectively and the most common plastic colour found was white (27% by number). There was a significant difference in the percentage by the occurrence of plastic across regions, founding the highest score of plastic on the central coast of Perú. We also found a significant relationship between the percentage occurrence of plastic debris in pellets and the presence of river mouths closer to the colonies. Plastic ingestion by guanay cormorants reveals that plastic has already been transferred into the Peruvian marine food web. This study is the first of its kind in the Peruvian marine environment and the results set a baseline for future studies of plastic pollution in the Peruvian sea.

**Authors:**

Isabella Diaz¹, Carlos Zavalaga¹, Bethany Clark²

¹Universidad Cientifica del Sur, ²BirdLife International

Guanay cormorant pellets (Phalacrocorax bougainvillii) as an indicator of marine plastic pollution along the Peruvian coast

**Abstract:**

Brown skuas (Stercorarius antarcticus lonnbergi) are opportunistic predators and scavengers. Here, we measured total mercury (THg) concentrations in blood samples from adult brown skuas (n = 82) from three breeding sites across a latitudinal gradient in the Southern Ocean (SW Atlantic region): (i) Bahía Esperanza/Hope Bay, Antarctic Peninsula; (ii) Signy Island, South Orkney Islands; and, (iii) Bird Island, South Georgia. Blood THg concentrations increased from high Antarctic to low Antarctic latitudes, such that Hg contamination was lowest at Bahía Esperanza/Hope Bay (mean ± SD, 0.95 ± 0.45 µg g-1 dw), intermediate at Signy Island (3.42 ± 2.29 µg g-1 dw) and highest at Bird Island (4.47 ± 1.10 µg g-1 dw). Blood THg concentrations were also related positively to δ15N values, reflecting the biomagnification process. Males had higher Hg burdens than females, likely reflecting deposition into the egg by females and potentially differences in trophic ecology. These data provide important insights into Hg transfer to Southern Ocean seabirds.

**Authors:**

William Mills¹, Andrés Ibañez², Paco Bustamante³, Ana Carneiro⁴, Stuart Bearhop⁵, Yves Cherel³, Rocío Mariano-Jelicich⁶, Rona McGill⁷, Diego Montalti², Stephen Votier⁸, Richard Phillips¹

¹British Antarctic Survey, ²Museo de La Plata (FCNyM-UNLP, CONICET), ³CNRS-La Rochelle Université, ⁴BirdLife International, ⁵University of Exeter, ⁶Universidad Nacional de Mar del Plata, ⁷Scottish Universities Environmental Research Centre, ⁸Heriot-Watt University

Latitudinal and sex differences in mercury contamination of brown skuas in the Southern Ocean

**Abstract:**

The study of the use of space in seabirds had increased exponentially due to the use of biologging devices and the statistical techniques to extract and analyze large datasets. One of these statistical techniques is the Hidden Markov Models (HMM), which allow the identification of different behaviors of birds during their trips. Currently, few studies have been carried out to evaluate the classification accuracy of HMMs at different sampling frequencies. In this sense, the goal of the present study is to quantify the effect of sampling frequencies on the identification of foraging areas using HMMs in two tropical seabirds (31 trips of Sula leucogaster and 16 trips of Phaethon aethereus), with different GPS sampling frequencies (1/min and 1/15min, respectively). In addition, in both species we used pressure sensor data where dives were identified, used to validate HMM results. To identify foraging states we fitted HMMs to GPS datasets from both seabirds. To validate the classification accuracy of the HMMs, the data classified as foraging were contrasted with the dives and were calculated the precision, sensitivity and specificity measures. Subsequently, kernel densities were estimated for foraging and dives datasets and the overlap between them was calculated as a proxy for overall accuracy. Results showed that the classification ability of the HMMs was 81% for S. leucogaster, while for P. aethereus it was 48%. On the other hand, the kernel overlap values of foraging and diving were higher than 95% for both species. The present study demonstrated that the classification ability of HMMs in data with low sampling frequency (i.e. 1/15min) could present a high error percentage at the individual level. However, the high kernel overlap value (>95%) shows that at the population level it is possible to use low sampling frequencies to identify foraging areas.

**Authors:**

Fiorella Vilela¹, Sophie Bertrand², Marcio A. Efe³, Leandro Bugoni⁴, Guilherme T. Nunes¹

¹Universidade Federal do Rio Grande do Sul, ²Institut de Recherche pour le Développement (IRD), ³Federal University of Alagoas, ⁴Universidade Federal do Rio Grande

The summer migration of the Yelkouan Shearwater (Puffinus yelkouan) from a single island in Croatia

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