United States

**Abstract:**

Knowledge of sexual differences in diet composition is key to properly understand aspects of seabird life history, their role in marine food webs, and how human activities such as fisheries may differentially affect individuals of each sex. We assessed differences in diet composition between male and female Imperial Cormorants (&lt;i&gt;Leucocarbo atriceps&lt;/i&gt;) breeding at Islas Blancas (44°46´S, 65°39´W), Argentina. Imperial cormorants show sexual size dimorphism, with males being 18% heavier than females. We obtained stomach samples through induced regurgitation from 60 adult individuals, 10 of each sex during three stages of the breeding cycle (incubation, small chicks and large chicks) in 2019. At least 11 and 28 prey taxa were recorded in stomach samples of males and females, respectively. Females consumed a greater diversity of prey species and a significantly higher number of prey items per stomach content. A two-way crossed analysis of similarities showed significant sex differences in diet composition in terms of numerical frequency along the breeding cycle. Males mainly consumed demersal species, with Argentine Red Shrimp Pleoticus muelleri (43.6%) and Argentine Hake Merluccius hubbsi (35.9%) being the main prey during incubation, and hake (&gt;77%) the dominant prey during both chick rearing stages. Females preyed upon benthic species mostly inhabiting rocky reefs. Prey with higher representation in the diet in the three stages analyzed were the fishes Patagonotothen spp. (30.84%, 36.43% and 19.37%). Results show a clear sexual segregation in the diet of Imperial Cormorants, in agreement with studies in other dimorphic seabirds, and also suggest that sex differences reflect the spatial segregation in feeding behavior of male and female individuals. Males and females may be playing different roles in coastal food webs and may be differentially affected by coastal trawl fisheries as hake and shrimp are their main target species.

**Authors:**

Cynthia Ibarra¹, Nicolás Suárez¹, Juan Ignacio Cortés¹, Ximena Navoa², Cristian Silva³, Pablo Yorio¹

¹Centro para el Estudio de Sistemas Marinos - CONICET, ²UNPSJB- Instituto de Investigación de Hidrobiología, ³Universidad Nacional de la Patagonia San Juan Bosco

3rd World Seabird Conference

Sexual segregation in the diet of the dimorphic Imperial Cormorant breeding in northern Argentine Patagonia

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:**

Knowledge of sexual differences in diet composition is key to properly understand aspects of seabird life history, their role in marine food webs, and how human activities such as fisheries may differentially affect individuals of each sex. We assessed differences in diet composition between male and female Imperial Cormorants (<i>Leucocarbo atriceps</i>) breeding at Islas Blancas (44°46´S, 65°39´W), Argentina. Imperial cormorants show sexual size dimorphism, with males being 18% heavier than females. We obtained stomach samples through induced regurgitation from 60 adult individuals, 10 of each sex during three stages of the breeding cycle (incubation, small chicks and large chicks) in 2019. At least 11 and 28 prey taxa were recorded in stomach samples of males and females, respectively. Females consumed a greater diversity of prey species and a significantly higher number of prey items per stomach content. A two-way crossed analysis of similarities showed significant sex differences in diet composition in terms of numerical frequency along the breeding cycle. Males mainly consumed demersal species, with Argentine Red Shrimp Pleoticus muelleri (43.6%) and Argentine Hake Merluccius hubbsi (35.9%) being the main prey during incubation, and hake (>77%) the dominant prey during both chick rearing stages. Females preyed upon benthic species mostly inhabiting rocky reefs. Prey with higher representation in the diet in the three stages analyzed were the fishes Patagonotothen spp. (30.84%, 36.43% and 19.37%). Results show a clear sexual segregation in the diet of Imperial Cormorants, in agreement with studies in other dimorphic seabirds, and also suggest that sex differences reflect the spatial segregation in feeding behavior of male and female individuals. Males and females may be playing different roles in coastal food webs and may be differentially affected by coastal trawl fisheries as hake and shrimp are their main target species.

**Authors:**

Cynthia Ibarra¹, Nicolás Suárez¹, Juan Ignacio Cortés¹, Ximena Navoa², Cristian Silva³, Pablo Yorio¹

¹Centro para el Estudio de Sistemas Marinos - CONICET, ²UNPSJB- Instituto de Investigación de Hidrobiología, ³Universidad Nacional de la Patagonia San Juan Bosco

poster

**Abstract:**

To prevent additional seabird extinctions, conservation practitioners need to know what species to focus on, what actions to take, and where to take them. We created a spatially explicit meta-population viability analysis (mPVA) model for all IUCN threatened (Critically Endangered, Endangered, Vulnerable) seabirds. We generated the model parameters by combining a global database on the breeding location, population meta structure, and anthropogenic threats to seabirds with a detailed seabird demographic and population database. Potential conservation interventions can be entered into the model to estimate the change they will have on extinction risk. We completed an extinction risk analysis for 94 insular threatened seabird species to determine which species are at Extreme (>75% of model runs predicted species extinction) or High (50 - 75% of model runs predicted species extinction) risk of extinction within 100 years. Our analysis identifies five conservation priorities and opportunities: 1) seabird species at extreme or high risk of extinction in the next century, 2) families of seabirds (Procellarids) that include the largest proportion of species with extreme or high risks of extinction, 3) the potential for mitigation of extinction risk to be gained by conducting all feasible eradications of damaging invasive vertebrates on at least one breeding island of extreme/high risk seabirds, 4) the potential for mitigation of extinction risk to be gained by conducting translocations/reintroductions to establish/re-establish breeding colonies of extreme/high risk seabirds, and 5) opportunities where innovation of new tools or competencies will significantly reduce the probability of extinction of threatened seabirds.

**Authors:**

Donald Croll¹, Kelly Zilliacus¹, M. Tim Tinker², Diana Ruiz¹, Bernie Tershy¹

¹University of California, Santa Cruz, ²Nhydra Ecological Consulting

Global meta-population viability analysis determines relative extinction risk among threatened seabirds

**Abstract:**

Against a general pattern of guillemot's reduction in colonies along Murman coast (Russia, southwestern part of the Barents Sea) large-scale fluctuations in their number were observed. In 2000-2018 in four colonies the number of Common and Brunnich's guillemots has decreased by 66% and 81% respectively with maximum drop in numbers of both species was recorded in one of them, by 71 and 90%respectively. It was established that the number of Common and Brunnich's guillemots in Murman colonies largely depends on availability and size of capelin spawning stocks in winter and spring. Capelin spawning and feeding areas do not remain constant and vary from year to year depending on the Barents Sea water masses temperature. Positive anomalies in water temperature contribute to more powerful capelin accumulations occur and rapidly increase in its abundance in the southern regions of the Barents Sea and off the Kola Peninsula coast. In these years favorable feeding conditions for seabirds may exist in pre-breeding period in Eastern Murman area. Spawning stocks of capelin move eastward in warm years resulted in trophic conditions in the western regions, and possibly along the Murman coast may deteriorate. In such years comparing to years with normal temperature conditions, a restricted capelin stock can be distributed over a wider water area. Evaluating trophic conditions for the guillemots, the impact of the fishing fleet which regularly reduces capelin stocks must be considered. Their restoring occurs with the advent of high-yielding generations, caused a subsequent fishing recovery. Combination of restricted recruitment and intensive fishing can significantly destroy guillemots' food supply in the southwestern part of the Barents Sea. The degradation of guillemot's colonies is due to impact of a complex of factors, including abundance and availability of capelin stocks, capture level and temperature regime of water masses determining distribution of capelin in coastal waters.

**Authors:**

Alexey Ezhov¹, Yuri Krasnov¹, Natalia Nikolaeva²

¹Murmansk Marine Biological Institute KSC RAS, ²Lomonosov Moscow State University

Status of colonies and factors determining the development of Common (Uria aalge) and Brünnuch's (U. lomvia) guillemot's populations on Murman coast southwestern part of the Barents Sea

**Abstract:**

The Arctic is warming faster than other regions of the Earth. The little auk, or dovekie (Alle alle) as an endemic Arctic organism may be especially prone to climate change. It is a small zooplanktivorous seabird with breeding range restricted to the High Arctic. We modelled current and future distribution of a foraging little auks in one of the most important breeding areas, Svalbard, using a combination of GPS-tracking, satellite remote sensing and data-driven (conditional inference tree) and expert-knowledge (fuzzy logic) based techniques. We characterized environmental conditions (sea surface temperature, sea depth, presence/absence of marginal sea ice zone) at foraging positions of GPS-tracked individuals from three breeding colonies in Svalbard: one 'boreo-Arctic' located at the boundary of Low Arctic and High Arctic zones and two 'high-Arctic' colonies located in the largest breeding aggregations of this species in Svalbard on the west coast of Spitsbergen. The birds from one 'high-Arctic' colony, influenced by cold Arctic water, foraged in the shallow shelf zone near the colony. The birds from the remaining colonies foraged in a wider range of depths, in a higher sea surface temperature zone ('boreo-Arctic') or in the productive but distant marginal sea ice zone (second 'high-Arctic' colony). Given this flexible foraging behaviour and results of studies on their breeding performance, little auks may be temporarily resilient to moderate climate changes. However, our fuzzy logic models of future distribution under scenarios of increased sea surface temperature by 1oC and 2oC SST, predict losses of feeding habitat within the cost-effective range of foraging flights for the majority of little auk colonies in Svalbard. Over longer time scales negative consequences of global warming are inevitable. The actual response of little auks to future environmental conditions will depend on the range of their plasticity and pace of ecosystem changes.

**Authors:**

Dariusz Jakubas¹, Katarzyna Wojczulanis-Jakubas¹, Lech Iliszko¹, Hallvard Strøm², Lech Stempniewicz¹

¹University of Gdansk, ²Norwegian Polar Institute

Current and future foraging habitat niche of a High Arctic zooplanktivorous seabird, the little auk Alle alle

**Abstract:**

Recent changes in our long-term study site (25 yrs) in the Bay of Fundy/Gulf of Maine have drawn us to examine the variety of mechanisms that might be affecting the alcids breeding there, given recent exceptionally rapid ocean warming and associated changes in diet. Seabirds are endotherms so manage their own temperature internally; but their prey are ectotherms whose physiology responds directly to changes in the marine environment. I consider some consequences of this 'metabolic asymmetry' on the availability of fish to seabird predators. Fish metabolic rate rises with water temperature, so more energy is needed for metabolism leaving less for growth; yet their ability to secure oxygen declines both because of haemoglobin's reduced affinity to bind oxygen in warmer water, and because warmer water holds less oxygen. The 'burst speed' of fish also increases with temperature, so fish prey are not only fewer (from reduced survival) and smaller (from slower growth) but harder to catch. It is to this increasing mismatch of predator and prey that the dearth of pursuit-diving seabirds in tropical oceans has been attributed. Changes lower in the food-chain add to these challenges for marine birds. In many phytoplankton communities, diatoms tend to be replaced by dinoflagellates; diatoms are the major source of 'essential' (unsaturated) fatty acids (UFAs) in marine ecosystems, which therefore become depleted. UFAs are important in maintaining flexibility in cell membranes, allowing cells to adjust to low temperatures, and therefore predominate in cold-water fish; warm-water fish have no need to maintain cell structure at low temperatures and contain less lipid, in which saturated fatty acids predominate. Fish prey available to seabirds as the ocean warms are likely to be fewer, smaller, faster, and less nutritious ('junk food') than those currently available to seabirds in boreal and arctic waters.

**Authors:**

Tony Diamond¹

¹University of New Brunswick

Fewer, faster, leaner: a seabird's-eye view of chasing fish in a warming ocean; mechanisms from cell membranes to body-size selection

**Abstract:**

In 2014, Spain declared 39 marine Special Protected Areas (SPA) in order to protect the 10% of its waters. European Storm Petrel has been identified as one of the key species to delimitate and declare the SPA for seabirds in the Gulf Cádiz, in the framework of Natura 2000 marine Network. This migratory species uses this area during their post-breeding migration for foraging and the SPA should guarantee its protection. This study analyse the distribution area of the European Storm Petrel and the oceanographic features related to in the Gulf of Cadiz using data of 10 years of oceanographic vessel campaigns to figure out the Key Area of the species in region. We conducted 103 census units during 2006-2018 covering more than 5,000 km and we detected 361 European Storm Petrel in 99 census units. We used Kernel Density Estimation to calculate the home range of the species and predictive Maxent models to determinate which oceanographic variables influence this petrel distribution. Our results show that the key area of the species was displaced to the west from to the current protected area, so this species could be not well adequately protected in the area. Using Maxent approach, the distance to Guadiana river mouth, distance to the Continental Platform and the concentration of Chlorophyll a have been identified as the main environmental variables that explain the European Storm Petrel distribution in the Gulf of Cádiz. These results contribute to a better understanding of the dynamic of the regional distribution of marine species and help to define a more suitable SPA and its management

**Authors:**

Andres de la Cruz Muñoz¹, Gonzalo Muñoz Arroyo¹

¹University of Cadiz

Unprotected key areas of European Storm Petrel in the Gulf of Cadiz, Spain

**Abstract:**

The most recent assessment of threats to seabirds at the global level confirmed that Invasive Alien Species (IAS), bycatch and climate change are the main drivers of decline of several species. Most seabirds, especially globally threatened ones, face multiple threats. IAS affects the highest number of species, but bycatch has a greater impact in terms of severity. In this study, we used data collected for the global revision to analyse in detail the threats facing seabirds occurring in Europe and in the EU28 (pre-2018). We found that, at European level, the main perils on land are hunting/trapping, pollution and IAS (affecting 46.8 %, 35.1 % and 33.8 % of species respectively). At sea, the main threats are bycatch (33.8 %), climate change/severe weather and overfishing (both 22.1 %). Marine threats have the greatest average impact on European species, even though they affect a smaller percentage of them compared to the major threats on land. In Europe, seabirds are among the bird families with the higher proportion of threatened and nearly threatened species (34,5% at EU level according to the last EU 2020 Red List assessment), with c. 25% experiencing population declines (especially Podicipedidae and Anatidae families). The study sheds light on the main threats faced by European seabirds during different phases of their annual cycles for both breeding and wintering species, and will contribute to the identification of key species and the measures needed to mitigate their most critical and deadly threats. In addition, this analysis will help guide current and future conservation and policy work in the region to drive effective conservation measures and identify where there is a shared political responsibility with third-party countries. This is particularly important for some highly mobile European species that spend a significant amount of time in the high seas where they encounter threats that have an impact on their survival.

**Authors:**

Antonio Vulcano¹, Maria Peixe Dias¹, Anna Staneva¹, Daniel Mitchell², Claire Rutherford¹

¹BirdLife International, ²Stichting BirdLife Europe

Threats to seabirds in Europe: a regional review

**Abstract:**

Viability assessments require long time series which are usually uncommon and often expensive. Rock shags (Phalacrocorax magellanicus, RS) inhabit the southern coasts of Argentina and Chile, and 8 % of the Argentinian population occurs along the Beagle Channel (BC). They nest in cliffs in several islands, and tourism activity does not seem to affect the number of breeding pairs. The Fuegian archipelago is also inhabited by several invasive species, one of which, the American Mink Neovison vison is a well-documented seabird nest predator. In this study We attempt to estimate the effect of invasibility on the viability of the RS population in the BC to recommend local management measures. We used counts of breeding pairs of RS in the BC, from 1994 to 2019 (yearly since 2007), to estimate the intrinsic growth rate (λ) for the overall population. We explore associations between λ and distance to the closest island of the archipelago where American Mink is present. We clustered sites in 'inshore' islands (<1 km to the mainland, n= 5) and 'offshore' islands (>2.5 km, n= 17), and calculated the absolute values of viability for the population for the next 50 years. High inter-annual variability was recorded, especially on offshore islands. Overall population decreased 2 % annually, from 691 breeding pairs in 1994 to 455 in 2019, and mean probability of extinction in 50 years was 17 %. This negative trend could be attributed mainly to the loss of the inshore population, while variation in growth rates were mainly due to variation in offshore colonies. While in 40 % of the inshore islands a local extinction was recorded, on the offshore islands the records of local extinctions and colonization were similar. In cormorants, site fidelity is usually high, thus a rapid response to disturbance is not expected. Although we know of a few colonies in the Chilean part of the channel that could be harboring emigrants from these islands, we were able to identify islands which are susceptible to be managed by Argentine government, with specific expected outcome in case of success.

**Authors:**

Ulises Balza¹, Sabrina Harris¹, Ricardo Sáenz-Samaniego¹, Mónica Torres¹, Natalia Rosciano², Marcela Liljeström¹, Andrea Raya-Rey¹

¹Centro Austral de Investigaciones Científicas (CADIC-CONICET), ²Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA-CONICET)

Rock shag inshore island colonies at risk in an invaded scenario

**Abstract:**

The yellow-legged gull (Larus michahellis) is a common seabird species around the Mediterranean coast, well adapted to exploit human-associated resources. As this species can carry a range of infectious agents, some of specific public health concern, understanding its movement ecology can provide essential information for predicting disease risk and pathogen emergence. This study aimed to characterize movement in this species using a multi-event mark-recapture modeling framework. The data included the encounter histories of 5158 birds marked at fledging between 1999 and 2004 at 14 colonies in southern France and resighted for 10 years. Our results show that young individuals have a greater mobility than older ones; 53% of juveniles are migratory during the non-breeding period and move to areas more than 50 km from the natal colony compared to only 24% in older birds that return to the breeding colony. However, the spatial extent of juvenile movements depend on colony location, with a 45% difference in the proportion of sedentary individuals between colonies 50 km apart. These differences may be explained by colony quality or population dynamics. Indeed, young birds from colonies with strong juvenile survival probabilities (~0.75) appear to be more sedentary than those from colonies with low survival probabilities (~0.36). These results indicate that young birds are likely be more important dispersers of avian disease than older birds and that this propensity may be conditioned by local breeding success, which itself may depend on the presence of parasites/pathogens.

**Authors:**

Charly Souc¹, Thomas Blanchon², Marion Vittecoq³, Rémi Choquet⁴, Karen McCoy⁵

¹MIVEGEC, University of Montpellier CNRS IRD / Tour du Valat, Research Institute for the Conservation, ²Tour du Valat, Research Institute for the Conservation of Mediterranean Wetlands, ³Tour du Valat, Research Institute for the Conservation of Mediterranean Wetlands / Centre for Resear, ⁴CEFE, University of Montpellier CNRS, ⁵MIVEGEC, University of Montpellier CNRS IRD / Centre for Research on the Ecology and Evolution of Di

Oh, the places you?ll go! Juvenile movements in the yellow-legged gull (Larus michahellis) in relation to the natal colony and its epidemiological importance

**Abstract:**

Population viability analysis (PVA) is a well-used approach for assessing how changes to vital rates will impact population dynamics, and is commonly used in environmental impact assessments to quantify potential threats to seabirds. These models typically do not account for density dependent regulation because the strength of these relationships is poorly understood. However, this omission is likely to influence the impact predicted by PVA, and thus compromise our understanding of seabird vulnerability to human activity. A small number of studies have demonstrated density dependent regulation in several species of seabird, however wider representation of the strength and direction of these relationships is lacking. In this study, we quantify the strength of density dependent regulation of breeding success in different species and populations of seabirds, addressing the likely bias in our understanding of its prevalence due to under-reporting of insignificant relationships. and examine how PVA predictions differ using five different structures for describing density dependent regulation. To do this we use long-term count and breeding success data collected from 30 populations and eight species of seabird that breed in the UK. We found evidence of positive and negative density dependent regulation that varied in strength and direction within and between species. Applying these relationship coefficients to theoretical populations of our study species using a pre-existing seabird specific PVA tool will allow us to measure the effect of differing strengths and models of density dependence on resulting rates of population change. Understanding the ways in which density dependence can be modelled in PVA and how it influences outcomes will facilitate more accurate environmental impact assessments for seabirds, and improve confidence in PVA findings.

**Authors:**

Eve Merrall¹, Jonathan Green¹, Leonie Robinson¹, Adam Butler², Matt Wood³, Mark Newell⁴, Francis Daunt⁴, Julie Black⁵, Cat Horswill⁶

¹University of Liverpool, ²Biomathematics and Statistics Scotland, ³University of Gloucestershire, ⁴UK Centre for Ecology & Hydrology, ⁵Joint Nature Conservation Committee, ⁶ZSL Institute of Zoology

Modelling density dependence in UK seabirds, in the context of population viability analysis

**Abstract:**

Changes in foraging strategies throughout the year are key determinants of seabird population dynamics. However, due to seabird post-breeding dispersal, year-round trophic ecology studies rarely focus on individuals from known colonies. Using stable isotope analysis (δ15N, δ13C) of blood and primary feathers, we tested during 2012 the trophic niche variation throughout the year in Kelp Gulls Larus dominicanus from three colonies in Patagonia, Argentina, located in areas with different availability of anthropogenic food subsidies. Isotopic niche width, measured using multivariate ellipse-based metrics, was wider at all colonies during the non-breeding season, suggesting that during this period gulls forage on a greater variety of food sources possibly related to post-breeding dispersal, seasonal changes in food resources, and/or the relaxation of central place foraging. Individuals from the colony with year-round availability of fisheries discards (Isla Vernaci) presented the lower isotopic niche width year-round compared to those from the other two colonies, one with discards only available during the breeding season (Punta Tombo) and the other with only open-air refuse dumps available all year-round (Punta León). At Isla Vernaci, an abrupt expansion in niche width occurred later in the non-breeding season, after the start of a fisheries moratorium, suggesting that Kelp Gulls remained in nearby areas and partly associated to trawl fisheries between breeding events. Preliminary diet results indicate that most studied individuals from Isla Vernaci were feeding on demersal prey, only available from fisheries discards as Kelp Gulls are surface feeders. These results suggest that the availability of discards can greatly influence Kelp Gull foraging strategies and non-breeding movements, and that changes in niche metrics can be context dependent. Future studies should complement the assessment of niche variability with studies of diet composition throughout the year.

**Authors:**

Nora Lisnizer¹, Alejandro Gatto¹, Pablo Yorio¹

¹Consejo Nacional de Investigaciones Científicas y Técnicas

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