Black-backed Gulls Research Articles

Varying foraging patterns in response to competition? A multicolony approach in a generalist seabird.

Reducing resource competition is a crucial requirement for colonial seabirds to ensure adequate self- and chick-provisioning during breeding season. Spatial segregation is a common avoidance strategy among and within species from neighboring breeding colonies. We determined whether the foraging behaviors of incubating lesser black-backed gulls (Larus fuscus) differed between six colonies varying in size and distance to mainland, and whether any differences could be related to the foraging habitats visited. Seventy-nine incubating individuals from six study colonies along the German North Sea coast were equipped with GPS data loggers in multiple years. Dietary information was gained by sampling food pellets, and blood samples were taken for stable isotope analyses. Foraging patterns clearly differed among and within colonies. Foraging range increased with increasing colony size and decreased with increasing colony distance from the mainland, although the latter might be due to the inclusion of the only offshore colony. Gulls from larger colonies with consequently greater density-dependent competition were more likely to forage at land instead of at sea. The diets of the gulls from the colonies furthest from each other differed, while the diets from the other colonies overlapped with each other. The spatial segregation and dietary similarities suggest that lesser black-backed gulls foraged at different sites and utilized two main habitat types, although these were similar across foraging areas for all colonies except the single offshore island. The avoidance of intraspecific competition results in colony-specific foraging patterns, potentially causing more intensive utilization of terrestrial foraging sites, which may offer more predictable and easily available foraging compared with the marine environment.

GPS tracking data of Lesser Black-backed Gulls and Herring Gulls breeding at the southern North Sea coast.

In this data paper, Bird tracking - GPS tracking of Lesser Black-backed Gulls and Herring Gulls breeding at the southern North Sea coast is described, a species occurrence dataset published by the Research Institute for Nature and Forest (INBO). The dataset (version 5.5) contains close to 2.5 million occurrences, recorded by 101 GPS trackers mounted on 75 Lesser Black-backed Gulls and 26 Herring Gulls breeding at the Belgian and Dutch coast. The trackers were developed by the University of Amsterdam Bird Tracking System (UvA-BiTS, http://www.uva-bits.nl). These automatically record and transmit bird movements, which allows us and others to study their habitat use and migration behaviour in great detail. Our bird tracking network is operational since 2013. It is funded for LifeWatch by the Hercules Foundation and maintained in collaboration with UvA-BiTS and the Flanders Marine Institute (VLIZ). The recorded data are periodically released in bulk as open data (http://dataset.inbo.be/bird-tracking-gull-occurrences), and are also accessible through CartoDB and the Global Biodiversity Information Facility (GBIF).

Mercury in marine fish, mammals, seabirds, and human hair in the coastal zone of the southern Baltic.

Mercury (Hg), aside from having high toxicity, is characterized by its ability to biomagnify in the marine trophic chain. This is an important problem especially in estuaries, or in the coastal zone, particularly near the mouths of large rivers. This study was conducted in the years 2001–2011, in the coastal zone of the Baltic Sea near to the mouth of the River Vistula, which is the second biggest river discharging into the Baltic. Mercury concentration was measured in the tissues and organs of cod, flounder, herring, seals (living in the wild and in captivity), great black-backed gulls, and African penguins from Gdańsk Zoo, and also in human hair. Penguins and seals at the seal sanctuary in Hel were fed only herring. In marine birds and mammals and in the pelagic herring, the highest Hg concentration was observed in the kidney and in the liver, while in cod and flounder (located on a higher trophic level) the muscles were the most contaminated with mercury. In gray seals living in the seal sanctuary, Hg concentration in all analyzed tissues and organs except the kidneys was lower in comparison with seals living in the wild. The comparatively small share of fish in the diet of local Polish people and their preference towards the consumption of herring contributed to low concentration of Hg in their hair. The protective mechanisms related to detoxification and elimination of mercury were shown to be more effective in the seals than in the penguins, despite the former consuming around 10 times more food per day.

Identifying Important Foraging Habitat for Colonial Waterbirds in an Urban Estuary: a Stable Isotope Approach

Abstract. Foraging habitat use by colonial waterbirds breeding in New York Harbor was examined to identify resources that were particularly important for the provisioning of young. Stable isotope values of carbon, nitrogen, and sulfur were measured in nestling waterbird feathers to determine the habitat type (ranging from marine to freshwater and anthropogenic) in which adults primarily foraged. Six species were investigated: Black-crowned Night-Herons (Nycticorax nycticorax), Great Egrets (Ardea alba), Glossy Ibises (Plegadis falcinellus), Double-crested Cormorants (Phalacrocorax auritus), Great Black-backed Gulls (Larus marinus), and Herring Gulls (L. argentatus). Waterbird populations exhibited both inter- and intra-specific variation in stable isotope values (P < 0.001), indicating variation in foraging habitat use among focal species across the estuary. Therefore, depending on the species-and region-specific conservation goal, management strategies would potentially need to target very different fora...

True navigation in migrating gulls requires intact olfactory nerves.

During migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from >60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, air-borne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.

Sexually distinct foraging strategies in an omnivorous seabird

Intra-specific differences in foraging behaviour can have fitness consequences, especially during breeding. We combined GPS tracking data from 34 lesser black-backed gulls (Larus fuscus) encompassing 2029 foraging trips with dietary information and morphometric measurements to test the effect of breeding status and sex as well as body size on foraging behaviour. We found sexually distinct foraging strategies in this generalist seabird, which were maintained throughout the breeding season. The larger males travelled further from the colony than females, spent more time offshore, and remained longer at the nest during nest bouts. Males fed mostly on fisheries discards at offshore trawlers with few alternative resources nearby. Females foraged predominantly on land or nearshore and in the Wadden Sea, where they had multiple foraging options. Individuals differed in foraging behaviour along a continuum of predominantly terrestrial to predominantly marine foragers. Foraging range, trip duration, and the proportion of time at sea increased with wing length. Our findings did not support the usual inference that sexual segregation is mediated primarily by differences in competitive strength as both sexes foraged substantially in competitive settings around fishing vessels, but in different habitats. Females accessed a wider variety of resources and a broad prey spectrum, by exploring a whole suite of foraging opportunities and habitats nearer the colony. Different behavioural strategies (a combination of individual specialisation and sexual segregation) during breeding could reduce intra-specific resource competition, competition between the sexes (and hence within a pair), or alternatively, reduce the risk of unbalanced food provisioning.

Human influence on gull non-breeding distribution: potential consequences of changes in fishing practices

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 527:221-232 (2015) - DOI: https://doi.org/10.3354/meps11282 Human influence on gull non-breeding distribution: potential consequences of changes in fishing practices Francisco Ramírez1,*, Carlos Gutiérrez-Expósito1, Isabel Afán2, Joan Giménez1, Renaud de Stephanis3, Manuela G. Forero1 1Departamento de Biología de la Conservación, and 2Laboratorio de SIG y Teledetección, Estación Biológica de Doñana (EBD-CSIC), Avda. Américo Vespucio s/n, 41092 Sevilla, Spain 3Conservation Information and Research on Cetaceans (CIRCE), Cabeza de Manzaneda 3, Algeciras-Pelayo, 11390 Cádiz, Spain *Corresponding author: ramirez@ebd.csic.es ABSTRACT: Interpopulation mixing of migratory species at particular stopover and wintering hotspots increases their vulnerability to anthropogenic impacts. Animal associations with human activities at this time of the annual cycle should, therefore, inform management policies. The Gulf of Cadiz, Spain is a key non-breeding area for the Near-Threatened Audouin’s gull Ichthyaetus audouinii and the over-abundant lesser black-backed gull Larus fuscus, both of which heavily depend on human fisheries. Here, we used long-term (1990-2013) data on coastal censuses, along with spatially-explicit information on fish landings (2000-2014) and on-board surveys of fishing vessels (2012-2013), to unravel the association of these gulls with human fisheries and evaluate its role in shaping their distribution at this important non-breeding hotspot. Fishing discards from trawlers were extensively used by lesser black-backed gulls, whereas Audouin’s gulls apparently benefited from fish aggregations that occurred where purse seines were retrieved. Fishing influence was identified as an important driver of the non-breeding distribution of these gulls, particularly for the lesser black-backed gull, which congregated near main fishing ports. Within this scenario, we speculate that changes in fishing practices, such as those proposed by the upcoming EU Reform of the Common Fisheries Policy that includes a ban on fishing discards, will almost certainly impact the lesser black-backed gull. In contrast, the impact on the Audouin’s gull remains unclear and will likely depend on how the proposed ban is implemented. KEY WORDS: Audouin’s gull · Lesser black-backed gull · Non-breeding distribution · Human fisheries · European Union Common Fisheries Policy Full text in pdf format PreviousNextCite this article as: Ramírez F, Gutiérrez-Expósito C, Afán I, Giménez J, de Stephanis R, Forero MG (2015) Human influence on gull non-breeding distribution: potential consequences of changes in fishing practices. Mar Ecol Prog Ser 527:221-232. https://doi.org/10.3354/meps11282 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 527. Online publication date: May 07, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Seabird–wind farm interactions during the breeding season vary within and between years: A case study of lesser black-backed gull Larus fuscus in the UK

The marine environment is increasingly pressured from human activities, such as offshore renewable energy developments. Offshore wind farms may pose direct risks to seabirds at protected breeding sites. However, changes in food availability may influence foraging behaviour and habitat use during the breeding season or between years. Consequently, seabird–wind farm interactions, and risks posed to populations, may vary over longer time scales, but this has seldom been quantified. We used GPS-telemetry to study the movements of 25 lesser black-backed gulls from the Alde–Ore Special Protection Area (SPA), UK between 2010 and 2012, while birds were associated with their breeding colony. Variation in movements away from the colony, offshore, and in operational, consented and proposed Offshore Wind Farm Areas (“OWFAs”) was investigated: (1) between years and (2) across the breeding season, addressing: (3) sex-specific, (4) individual and (5) diurnal/nocturnal differences. The extent of overlaps with OWFAs varied between years, being greatest in 2010 (7/10 birds showing connectivity; area overlap: 6.2±7.1%; time budget overlap: 4.6±6.2%) and least in 2012. Marine habitats close to the colony were used before breeding. Birds spent little time offshore as incubation commenced, but offshore usage again peaked during the early chick-rearing period, corresponding with use of OWFAs. Individuals differed in their seasonal interactions with OWFAs between years, and males used OWFAs significantly more than females later in the breeding season. This study demonstrates the importance of tracking animals over longer periods, without which impact assessments may incorrectly estimate the magnitude of risks posed to protected populations.

The accuracy of urban nesting gull censuses

Capsule The vantage point survey methods used in the 1999–2002 surveys of urban nesting large gulls in Britain and Ireland appreciably underestimated numbers, resulting in lower national totals and exaggerated national population changes, because they did not account for a substantial proportion of undetected nests.Aims To evaluate the efficiency of various survey methods for urban nesting large gulls.Methods Vantage point and street surveys of Herring and Lesser Black-backed Gulls Larus argentatus and Larus fuscus nests were made in six urban conurbations and used to compare detection efficiencies. Some nests missed by both methods were later identified by the presence of unfledged chicks. In later years, the numbers of nests which were actually missed was determined by using a ‘cherry-picker’ which allowed all nests to be located in Dumfries. The proportion of nests on industrial and commercial buildings was recorded.Results Vantage point and street surveys missed an appreciable number of nests and had average maximum nest detection rates of 78% and 48%, respectively. Combining the two methods raised the efficiency to a maximum of 88%. The detection rate varied inversely with the proportion of nest sites that were on commercial or industrial sites. The complete census of nests in Dumfries in 2013–14 showed that vantage point surveys detected only 75% of nests, while the combination of the two survey methods increased the detection rate to 84%.Conclusion Vantage point surveys markedly underestimate numbers of nesting large gulls. Surveys were less effective on conurbations where nesting gulls used a high proportion of industrial and commercial properties. Therefore the 1999–2002 national surveys in Britain and Ireland underestimated the numbers of urban nesting Herring and Lesser Black-backed Gulls and, as a result, may have exaggerated the national trends in abundance of both species. More intensive methods are required in surveys of urban nesting gulls and correction factors need to be established from very high vantage points by use of cherry-pickers or aerial surveillance.

Towards a cumulative collision risk assessment of local and migrating birds in North Sea offshore wind farms

Bird collision assessments are generally made at the scale of a single wind farm. While especially in offshore situations such assessments already hold several assumptions, even bigger challenges exist on estimating the cumulative impact of multiple wind farms and the impacts at population level. In this paper, the number of collision victims at Belgian offshore wind farms was estimated with a (theoretical) collision risk model based on technical turbine specifications, bird-related parameters and bird density data of both local seabirds and passerine migrants. Bird density data were gathered by visual censuses and radar registrations. The outcome of the model was extrapolated to future development scenarios in the Belgian part of the North Sea and in the entire North Sea, and then further used for a preliminary assessment of the impact at population level for the species at risk. The results indicate that the cumulative impact of a realistic scenario of 10,000 turbines in the North Sea might have a significant negative effect at population level for lesser and great black-backed gull. We further show that during a single night of intense songbird migration, the number of collision victims among passerine migrants might be in the order of magnitude of several thousands in the entire North Sea. We argue that it is of great importance to further develop methods to quantify the uncertainties and to minimise the assumptions, in order to assure more reliable cumulative impact assessments.

Individual specialization on fishery discards by lesser black-backed gulls (Larus fuscus)

Abstract While seabird–fishery associations are well documented, this research primarily comes from ship-based surveys and consequently individual level responses to discard availability are largely unknown. As part of a long-term study on lesser black-backed gulls (Larus fuscus) in the Netherlands, the fine-scale movements of adults were tracked with GPS tags throughout the breeding period. The aim of this study was to determine if lesser black-backed gulls were utilizing fishery discards in the Wadden Sea and to examine possible consequences of this behaviour. Within the Wadden Sea during weekdays, tracked birds predominately associated with zones where fishing vessels are known to operate (deep gullies). Across all individuals combined (n = 40), there was a significantly reduced use of the Wadden Sea during weekends when the fleets were not operating. Eight females, who markedly increased their use of the Wadden Sea during weekdays throughout the breeding period, were largely responsible for this pattern. The loss of discard resources on weekends primarily resulted in these eight individuals switching to terrestrial foraging areas. Nest attendance and total foraging time were consistent between weekdays and weekends, suggesting that resource shifts on weekends did not impact daily time budgets. As such, it appears that lesser black-backed gulls specializing on discard utilization are able to flexibly respond to the temporary loss of discards by switching to alternative resources.

Colonial Marine Birds Influence Island Soil Chemistry Through Biotransport of Trace Elements

Marine birds are important vectors of nutrient and contaminant transfer from sea to land. In eastern Nova Scotia, Canada, colonial marine birds nest on specific nearshore islands within archipelagoes, and we predicted that soils on islands with bird colonies would have higher concentrations of selected trace elements (notably K, Ca, As, Cd, Cu, Pb, Se, Hg, and Zn) than soils on islands without colonies. In this study, common eider (Somateria mollissima), Leach’s storm petrel (Oceanodroma leucorhoa), black guillemot (Cepphus grylle), double-crested cormorant (Phalacrocorax auritus), great black-backed gull (Larus marinus), and herring gull (Larus argentatus) were considered to be the principal avian vectors for contaminant transfer. Results indicate that soils from islands with bird colonies had unique chemical compositions and commonly displayed elevated concentrations of K, Ca, Cu, Se, and Zn when compared to islands without colonies. Thus, marine birds feeding in the nearby marine zone move pollutants and nutrients from the ocean to nesting islands, potentially influencing habitat quality for coastal terrestrial species.

Variation in immune parameters and disease prevalence among Lesser Black-backed Gulls (Larus fuscus sp.) with different migratory strategies.

The ability to control infections is a key trait for migrants that must be balanced against other costly features of the migratory life. In this study we explored the links between migration and disease ecology by examining natural variation in parasite exposure and immunity in several populations of Lesser Black-backed Gulls (Larus fuscus) with different migratory strategies. We found higher activity of natural antibodies in long distance migrants from the nominate subspecies L.f.fuscus. Circulating levels of IgY showed large variation at the population level, while immune parameters associated with antimicrobial activity showed extensive variation at the individual level irrespective of population or migratory strategy. Pathogen prevalence showed large geographical variation. However, the seroprevalence of one of the gull-specific subtypes of avian influenza (H16) was associated to the migratory strategy, with lower prevalence among the long-distance migrants, suggesting that migration may play a role in disease dynamics of certain pathogens at the population level.

Hatching success in Lesser Black-backed Gulls Larus fuscus - an island case study of the effects of egg and nest site quality

Within an avian breeding population, there can be considerable variation in egg and nest site characteristics that have implications for individual reproductive success. Here we present a detailed case study of Lesser Black-backed Gulls Larus fuscus nesting on Flat Holm island, Wales, at a time when the colony was growing. This species is ground-nesting, with a modal clutch size of three. We surveyed 714 nests across the island during two consecutive years and recorded data on nest and egg characteristics, along with hatching success. We modelled how hatching success was associated with clutch size, egg volume, egg laying order and local habitat features, i.e. the amount of vegetation surrounding the nest and each nest's proximity to neighbouring nests. Eggs were most likely to hatch when they were laid in the middle of the season, were large in size, part of big clutches and in nests with a substantial amount of surrounding vegetation. Lesser Black-backed Gull productivity is currently low in many protected rural and coastal colonies throughout this species' range. Detailed information on factors influencing reproductive success could therefore indicate ways in which this species could be better managed to help maintain and conserve breeding populations.

British Ornithologists' Union Records Committee: 43rd Report (October 2014)

British Ornithologists' Union Records Committee: 43rd Report (October 2014)

Contaminant levels in Herring (Larus argentatus) and Great Black-backed Gull (Larus marinus) eggs from colonies in the New York harbor complex between 2012 and 2013.

Birds living in coastal areas are exposed to severe storms and tidal flooding during the nesting season, but also to contaminants that move up the food chain from the water column and sediment to their prey items. We examine metals in Herring Gull (Larus argentatus) and Great Black-backed Gull (Larus marinus) eggs collected from the New York/New Jersey harbor estuary in 2012 and in 2013 to determine if there were significant yearly differences in metal levels. We test the null hypothesis that there were no significant yearly differences in metal levels. We investigate whether there were consistent differences in metals from 2012 to 2013 that might suggest a storm-related effect because Superstorm Sandy landed in New Jersey in October 2012 with high winds and extensive flooding, and view this research as exploratory. Except for arsenic, there were significant inter-year variations in the mean levels for all colonies combined for Herring Gull, and for lead, mercury and selenium for Great Black-backed Gulls. All metal levels in 2013 were less than in 2012, except for lead. These differences were present for individual colonies as well. Metal levels varied significantly among islands for Herring Gulls in both years (except for cadmium in 2013). No one colony had the highest levels of all metals for Herring Gulls. A long term data set on mercury levels in Herring Gulls indicated that the differences between 2012 and 2013 were greater than usual. Several different factors could account for these differences, and these are discussed.

Metal Levels in Eggs of Waterbirds in the New York Harbor (USA): Trophic Relationships and Possible Risk to Human Consumers

Health professionals are interested in evaluating the risks that heavy metals pose to eco-receptors and humans. The objective of this study was to examine levels of mercury (Hg), lead (Pb), cadmium (Cd), and other contaminants in waterbirds nesting in the New York harbor in 2012 to determine (1) whether there were species and locational differences, and (2) whether consumption of eggs posed a health risk to predators or humans. For arsenic (As), Pb, Hg, and selenium (Se), species contributed more to variations in levels than location; for Cd and chromium (Cr), location was more significant. Mean metal levels differed among species for all metals, except Cd. Highest levels were As (great black-backed gulls, Larus marinus), Cr (great egret, Ardea alba), Pb (Canada goose, Branta canadensis), and Hg and Se (black-crowned night heron, Nycticorax nycticorax). There were significant locational differences only for herring gulls (Larus argentatus); significant differences were found for all metals. Levels of Hg and Pb may be sufficiently high in eggs of some species to produce adverse effects in predators that eat them. The proportion of samples above 0.3 ppm Hg (U.S. Environmental Protection Agency [EPA] freshwater criteria for freshwater fish), the contaminant of health concern, ranged from 0% (Canada goose, great egret), to 14 and 27% in gulls, to 50% (black-crowned night heron). Some herring gull, great black-backed gull, and black-crowned night heron eggs had 0.5 ppm or higher Hg. Thus, human consumption of eggs may pose a risk to fetuses and young children.

Use of LC-MS-MS as an alternative to currently available immunoassay methods to quantitate corticosterone in egg yolk and albumen.

Corticosterone (CORT) is the dominant plasma glucocorticoid in birds. There has been increasing interest in the function of CORT in avian egg yolk and in the potential to use CORT concentrations in eggs to quantify stress and to assess the effect of maternal stress on offspring. The concentration of CORT in egg yolk is most frequently assessed using enzyme or radioimmunoassays, alone or in combination with high-performance liquid chromatography. However, the quantification of CORT is frequently hampered by the presence of high concentrations of other steroid hormones which cross-react with the CORT antibody. As an alternative, we developed a sensitive and specific LC-MS-MS method. The sample-preparation procedure consisted of a protein-lipid precipitation step, followed by defatting and clean-up using a C18 SPE column. Chromatography was performed on an Acquity C18 BEH column (50 mm × 2.1 mm i.d., dp: 1.7 μm, run-time: 6 min), using 0.1% formic acid in both water (A) and acetonitrile (B) as mobile phases. The MS-MS instrument was operated in the positive-electrospray-ionization mode. The method was validated in-house according to European Guidelines (linearity, accuracy and precision, limits of quantification and detection, specificity, stability) and the results fell within the accepted ranges. The method was successfully used for the analysis of CORT in yolk and albumen of eggs collected from eight breeding lesser black-backed gulls at a Flemish coastal colony. CORT concentrations were in the range 42.4-166.3 pg g(-1) in albumen and < LOQ (75 pg g(-1))-762.5 pg g(-1) in yolk.

Gull diets reveal dietary partitioning, influences of isotopic signatures on body condition, and ecosystem changes at a remote colony

As top predators that feed on a wide range of prey items, gull diets may serve as important biological indicators of regional prey availability and changes in marine ecosystems. We studied the diets of herring gulls Larus argentatus and great black-backed gulls L. marinus on Sable Island, Nova Scotia, Canada, a remote colony which has shown high levels of contaminants in herring gull eggs and which has experienced significant ecological and anthropogenic change in its surrounding marine region over the past 40 yr. Analysis of regurgitated pellets suggested that current gull diets have proportionally less offshore prey (e.g. fish) and terns and tern eggs, and proportionally more molluscs, rock crabs Cancer borealis, and seal Halichoerus grypus car- rion than diets sampled 40 yr ago. The composition of recent diets observed from pellet analysis is supported by stable isotope mixing models of carbon (δ 13 C) and nitrogen (δ 15 N), which revealed that great black-backed gulls had high proportions of seals and crab in their diets, whereas her- ring gulls had high proportions of crab, sand lance Ammodytes sp., and terrestrial invertebrates. Isotopic analyses also identified dietary variability through seasonal, age-specific and body condi- tion relationships for each species. Biometricisotope relationships showed that larger great black-backed gulls fed at higher trophic levels, and that higher trophic level foraging in herring gulls was associated with better body condition. Collectively, these results indicate dietary parti- tioning within this community of sympatrically nesting gulls, and broad-scale dietary shifts since the early 1970s.

Seabird avoidance and attraction at an offshore wind farm in the Belgian part of the North Sea

Through before–after control-impact designed ship-based seabird surveys, seabird displacement occurring after the installation of an offshore wind farm at the Belgian Bligh Bank in 2010 was studied. Results demonstrate that northern gannet (Morus bassanus), common guillemot (Uria aalge) and razorbill (Alca torda) avoided the wind farm area, and decreased in abundance with 85, 71 and 64%, respectively. Lesser black-backed gull (Larus fuscus) and herring gull (Larus argentatus) were attracted to the wind farm, and their numbers increased by a factor 5.3 and 9.5. Other gull species too were found to frequent the turbine-built area, most notably common gull (Larus canus), black-legged kittiwake (Rissa tridactyla) and great black-backed gull (Larus marinus). The ecological incentives behind the observed attraction effects are still poorly understood, but on top of the increase in roosting possibilities it is plausible that offshore wind farms offer enhanced feeding opportunities. Importantly, attraction of seabirds to offshore wind farms implies an increased collision risk.