Lesser Black-backed Gull Larus Fuscus Research Articles

CORRIGENDUM: Thermal soaring over the North Sea and implications for wind farm interactions

Seabirds use several flight modes at sea, including thermal soaring, in which thermal uplift is used to gain altitude and save energy. An increase in flight altitude may have consequences for wind farm interactions if it results in birds spending more time within the rotor-swept zone (RSZ). To understand conditions under which thermal soaring occurs and potential implications for wind farm interactions, we investigated thermal soaring in relation to atmospheric conditions in June and July at 2 study areas in the North Sea, west and north of the Dutch coast. We developed algorithms that identified thermal soaring in GPS tracks of lesser black-backed gulls Larus fuscus and radar tracks of seabirds. By combining species-specific 3-dimensional information on flight behaviour from bio-logging with the continuous spatiotemporal coverage of radar positioned at wind parks, we obtained a more comprehensive overview of thermal soaring at sea than either method would obtain alone. Our results showed that birds flew at higher altitudes during thermal soaring than non-soaring flight, increasing the proportion of flight time within the RSZ. Thermal soaring occurred inside offshore wind farms to a similar degree as outside. Thermal soaring was positively correlated with positive temperature differences (ΔT) between sea surface and air (at 2 m above sea level), and north and north-westerly winds. We show that the probability of thermal soaring over the North Sea, inside and outside wind farms, increases with larger temperature differences, resulting in increased time spent within the RSZ and an increased collision risk for seabirds.

Flight heights obtained from GPS versus altimeters influence estimates of collision risk with offshore wind turbines in Lesser Black-backed Gulls Larus fuscus

The risk posed by offshore wind farms to seabirds through collisions with turbine blades is greatly influenced by species-specific flight behaviour. Bird-borne telemetry devices may provide improved measurement of aspects of bird behaviour, notably individual and behaviour specific flight heights. However, use of data from devices that use the GPS or barometric altimeters in the gathering of flight height data is nevertheless constrained by a current lack of understanding of the error and calibration of these methods. Uncertainty remains regarding the degree to which errors associated with these methods can affect recorded flight heights, which may in turn have a significant influence on estimates of collision risk produced by Collision Risk Models (CRMs), which incorporate flight height distribution as an input. Using GPS/barometric altimeter tagged Lesser Black-backed Gulls Larus fuscus from two breeding colonies in the UK, we examine comparative flight heights produced by these devices, and their associated errors. We present a novel method of calibrating barometric altimeters using behaviour characterised from GPS data and open-source modelled atmospheric pressure. We examine the magnitude of difference between offshore flight heights produced from GPS and altimeters, comparing these measurements across sampling schedules, colonies, and years. We found flight heights produced from altimeter data to be significantly, although not consistently, higher than those produced from GPS data. This relationship was sustained across differing sampling schedules of five minutes and of 10 s, and between study colonies. We found the magnitude of difference between GPS and altimeter derived flight heights to also vary between individuals, potentially related to the robustness of calibration factors used. Collision estimates for theoretical wind farms were consequently significantly higher when using flight height distributions generated from barometric altimeters. Improving confidence in telemetry-obtained flight height distributions, which may then be applied to CRMs, requires sources of errors in these measurements to be identified. Our study improves knowledge of the calibration processes for flight height measurements based on telemetry data, with the aim of increasing confidence in their use in future assessments of collision risk and reducing the uncertainty over predicted mortality associated with wind farms.

The Annual Cycle, Breeding Biology and Feeding Ecology of the Lesser Black-Backed Gull Larus fuscus

The Annual Cycle, Breeding Biology and Feeding Ecology of the Lesser Black-Backed Gull Larus fuscus

Seed Size, Not Dispersal Syndrome, Determines Potential for Spread of Ricefield Weeds by Gulls.

Recent field data suggest that migratory gulls disperse many rice field weeds by gut passage (endozoochory), most of which are dry fruited and widely assumed to have no long-distance dispersal mechanisms, except via human activity. We investigated this mechanism with a feeding experiment, in which seeds of five common rice field weeds (in order of increasing seed size: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis, Amaranthus retroflexus, and the fleshy-fruited Solanum nigrum) were fed to seven individuals of lesser black-backed gulls Larus fuscus held in captivity. We quantified seed survival after collecting faeces at intervals for 33 h after ingestion, then extracting intact seeds and running germination tests, which were also conducted for control seeds. All five species showed high seed survival after gut passage, of >70%. Gut retention times averaged 2-4 h, but maxima exceeded 23 h for all species. Germinability after gut passage was 16-54%, and gut passage accelerated germination in J. bufonius and S. nigrum, but slowed it down in the other species. All species had lower germinability after gut passage compared to control seeds (likely due to stratification prior to the experiment), but the loss of germinability was higher in smaller seeds. There was no evidence that the different dispersal syndromes assigned to the five species (endozoochory, epizoochory or barochory) had any influence on our results. In contrast, mean gut retention time was strongly and positively related to seed size, likely because small seeds pass more quickly from the gizzard into the intestines. Non-classical endozoochory of dry-fruited seeds by waterbirds is a major but overlooked mechanism for potential long-distance dispersal, and more research into this process is likely essential for effective weed management.

Gull-human interactions in an urban population of Herring Gulls Larus argentatus and Lesser Black-backed Gulls Larus fuscus

ABSTRACT Herring Gulls Larus argentatus and Lesser Black-backed Gulls Larus fuscus were involved in more nuisance events with humans as the breeding season progressed, although human provisioning was negatively associated with gull nuisance events.

Daily, seasonal, and annual variation in area use of Lesser Black-backed Gulls Larus fuscus related to offshore renewable developments

ABSTRACT Capsule Individually tracked Lesser Black-backed Gulls Larus fuscus rarely visited offshore areas in this study but showed high variation across multiple time scales in overall area use. Aims To quantify the variation in space use by Lesser Black-backed Gulls, a species of conservation concern, from short- and long-term data on tracked individuals, and to assess the time spent offshore and interacting with offshore wind farms (OWFs) before and after their construction. Methods GPS tracking data were collected between 2016 and 2019 from 36 Lesser Black-backed Gulls breeding in a declining colony in the UK with several operational OWFs nearby. Variations in home ranges, foraging trip metrics and the proportion of time spent offshore or within OWFs were analysed at three temporal scales: (i) over a daily cycle, (ii) across the breeding season and (iii) between years. Results Individuals predominantly used terrestrial areas. Less than 1.25% of the overall breeding season time budgets were spent offshore across years, and offshore use and time within OWFs did not vary significantly between years. However, home range sizes and foraging trip metrics did vary significantly across all time scales and individual variation was significant. Conclusion Our results suggested that there was little change in the relative use of offshore areas over time and thus in the macro-scale response of Lesser Black-backed Gulls to the OWFs, one of which was under construction during the period of study. Colony productivity and changes in the terrestrial environment were likely to be more important for influencing foraging movements at this colony.

Thermal soaring over the North Sea and implications for wind farm interactions

Seabirds use several flight modes at sea, including thermal soaring, in which thermal uplift is used to gain altitude and save energy. An increase in flight altitude may have consequences for wind farm interactions if it results in birds spending more time within the rotor-swept zone (RSZ). To understand conditions under which thermal soaring occurs and potential implications for wind farm interactions, we investigated thermal soaring in relation to atmospheric conditions in June and July at 2 study areas in the North Sea, west and north of the Dutch coast. We developed algorithms that identified thermal soaring in GPS tracks of lesser black-backed gulls Larus fuscus and radar tracks of seabirds. By combining species-specific 3-dimensional information on flight behaviour from bio-logging with the continuous spatiotemporal coverage of radar positioned at wind parks, we obtained a more comprehensive overview of thermal soaring at sea than either method would obtain alone. Our results showed that birds flew at higher altitudes during thermal soaring than non-soaring flight, increasing the proportion of flight time within the RSZ. Thermal soaring occurred inside offshore wind farms to a similar degree as outside. Thermal soaring was positively correlated with positive temperature differences (ΔT) between sea surface and air (at 2 m above sea level), and north and north-westerly winds. We show that the probability of thermal soaring over the North Sea, inside and outside wind farms, increases with larger temperature differences, resulting in increased time spent within the RSZ and an increased collision risk for seabirds.

Long-term impact on the breeding birds of a semi-offshore island-based wind farm in Åland, Northern Baltic Sea

Breeding bird populations were monitored at a wind farm in the Båtskär area of the southern Åland archipelago in 2006–2017. The area is situated in the outer archipelago and comprises four islands with six wind turbines in total. The wind turbines began operating in autumn 2007. An environmental impact assessment for the area was conducted in 2002. A control area called Stenarna, located 22 km NW of Båtskär, was used for comparison. The Båtskär area annually recorded 850–1,050 pairs of breeding birds. Four species showed significantly decreasing trends in Båtskär, namely the Common Eider Somateria mollissima, Lesser Black-backed Gull Larus fuscus, Herring Gull L. argentatus , and Black Guillemot Cepphus grylle. In Stenarna, only the Common Eider significantly decreased over the same period. The Arctic Tern Sterna paradisaea  increased in both areas, while the Velvet Scoter Melanitta fusca, Red-breasted Merganser Mergus serrator, Common Gull Larus canus, Rock Pipit Anthus petrosus, and White Wagtail Motacilla alba increased in Stenarna, the control area. The Herring Gull population decline is unlikely to be related to the wind farm. However, the proximity of a wind turbine to a breeding colony of the Lesser Black-backed Gull has most likely contributed to its decline. The reason for the Black Guillemot decline in Båtskär is unknown. The decline of Common Eider in both areas may be connected to increasing predation from White-tailed Eagles Haliaeetus albicilla. Some species, such as the House Martin Delichon urbicum and auks, have benefitted from the wind farm construction. They can utilize new microhabitats created by the construction, while other species, such as the Common Eider, gain protection against predation because of human activities.

Dispersal of aquatic invertebrates by lesser black-backed gulls and white storks within and between inland habitats

Waterbirds can transport aquatic invertebrates internally, contributing to metapopulation dynamics between aquatic habitats in a terrestrial matrix. However, research into this dispersal process to date has focused on individual field sites or laboratory studies. We investigated the invertebrates dispersed by endozoochory by the lesser black-backed gull Larus fuscus wintering in Andalusia, south-west Spain in 2016–2017, comparing seven sites interconnected by their movements, with different degrees of anthropogenization [three landfills, two saltpan complexes, a natural lake, and a large (370 km2) ricefield area]. In the ricefields, we also compared invertebrates dispersed by gulls with those dispersed by the larger white stork Ciconia ciconia. A total of 642 intact invertebrates and their propagules (mainly plumatellid bryozoans, cladocerans, and other branchiopods) were recorded in excreta (faeces and pellets) from gulls and storks. A greater diversity and abundance of invertebrates were recorded in ricefields, notably 43 individuals of the alien snail Physella acuta. One snail was still alive in a gull pellet 3 weeks after being stored in a fridge. This represents the first record of snail dispersal within waterbird pellets. Viability was also confirmed for the cladoceran Macrothrix rosea recorded in ricefields, and the alien brine shrimp Artemia franciscana recorded mainly in saltpans. In ricefields, gulls and pellets had significantly fewer propagules and fewer taxa per gram of excreta than storks and faeces, respectively. Through their high mobility, gulls and storks can disperse invertebrates between different natural and artificial habitats, and even to landfills. They can promote metapopulation dynamics for native bryozoans and branchiopods, but also the spread of invasive snails and brine shrimp.

Weather- and human-related shifts in feeding conditions promote the use of built-up areas by an avian opportunist

Human activities benefit a range of animal species, the resulting presence of which in cities can have negative societal consequences. One example are food subsidies, which buffer natural variation in food availability and allow these species to maintain larger populations. These buffers will likely gain importance under future environmental change whereby natural food sources become decreasingly available. To inform on the current importance of different habitats for a bird reliant on human-made food subsidies (Lesser Black-backed Gull Larus fuscus), and its possible population response toward changes in climate and the availability of these subsidies, we characterized population-level short-term responses to variation in drivers of local food availability, both natural (weather related) and anthropogenic (fisheries activity). We expected foraging effort to vary in relation to local wind speed and soil moisture, as well as to the alternation of fisheries activity between weekdays and weekends. Individuals were predicted to adjust their foraging habitat use in response to these environmentally driven variations in effort. To this end, we analyzed GPS tracking data of 45 breeding individuals, between 2013 and 2018, nesting in the Port of Zeebrugge, Belgium. Effort was approximated as the energy expenditure rate per trip, the daily time spent away from the colony and the trip frequency, which were analyzed by means of linear mixed effects models. Habitat use per trip was compared between marine, agricultural fields and built-up areas (cities, industry and cattle farms), in a multinomial logistic model. Marine areas and agricultural fields were most frequently exploited, but all considered stressors (wind, dry conditions and inactivity of fisheries) resulted in a higher use of built-up areas. Stronger winds increased the energetic cost of foraging at sea, and thus diminished the use of marine areas, as also did the inactivity of fisheries in weekends. Dry conditions diminished the use of fields and decreased trip frequency. Built-up areas thus constitute a buffer for the variation in food availability at sea and in agricultural fields. The expected increase in frequency and severity of extreme weather events (storms and drought) under global change, combined with the disappearance of discards, may therefore result in a long-term increase in the use of urban habitats by opportunistic large Gull species.

When speed matters: The importance of flight speed in an avian collision risk model

Renewable energy continues to grow globally, and the number of offshore wind farms is set to increase. Whilst wind energy developments provide energy security and reduced carbon budgets, they may impact bird populations through collision mortality, habitat modification and avoidance. To date, avian collision mortality has received the most attention and collision risk models have been developed to estimate the potential mortality caused by wind turbines. The utility of these models relies not only on their underlying assumptions but also on the data available to ensure the predictions are informative. Using a stochastic collision risk model (sCRM; based on the Band collision risk model) as an example, we explore the importance of bird flight speed and consider how the assumptions of the model influence the sensitivity to flight speed. Furthermore we explore the consequences of using site-specific GPS-derived flight speed rather than a standard generic value, with Lesser Black-backed Gulls Larus fuscus as an example, and consider how this generic value is currently used. We found that the model was most sensitive to the parameters of bird density, non-avoidance rate and percentage of birds at collision risk height, as well as bird flight speed. Using site-specific flight speed data derived from GPS tags rather than a standard value reduced the predicted number of collisions. We highlight that within the model, both the estimation of the probability of collision (PColl) and the flux of birds are sensitive to the bird flight speed; this sensitivity acts in opposite directions but the two do not necessarily balance out. Therefore, when the sCRM is used as generally done, there is little difference in collision estimates if airspeeds (bird flight speed relative to air through which it is moving) are used rather than groundspeeds (bird flight speed relative to ground). Estimates of seabird collision rates in relation to offshore wind farms are impacting future offshore wind development. By using site specific flight speed estimates and, accounting for different speeds in relation to wind direction, we demonstrate that cumulative collision estimates can be affected, highlighting the need for more representative flight speed data and where possible site-specific data.

Faecal microbiota and antibiotic resistance genes in migratory waterbirds with contrasting habitat use

Migratory birds may have a vital role in the spread of antimicrobial resistance across habitats and regions, but empirical data remain scarce. We investigated differences in the gut microbiome composition and the abundance of antibiotic resistance genes (ARGs) in faeces from four migratory waterbirds wintering in South-West Spain that differ in their habitat use. The white stork Ciconia ciconia and lesser black-backed gull Larus fuscus are omnivorous and opportunistic birds that use highly anthropogenic habitats such as landfills and urban areas. The greylag goose Anser anser and common crane Grus grus are herbivores and use more natural habitats. Fresh faeces from 15 individuals of each species were analysed to assess the composition of bacterial communities using 16S rRNA amplicon-targeted sequencing, and to quantify the abundance of the Class I integron integrase gene (intI1) as well as genes encoding resistance to sulfonamides (sul1), beta-lactams (blaTEM, blaKPC and blaNDM), tetracyclines (tetW), fluoroquinolones (qnrS), and colistin (mcr-1) using qPCR. Bacterial communities in gull faeces were the richest and most diverse. Beta diversity analysis showed segregation in faecal communities between bird species, but those from storks and gulls were the most similar, these being the species that regularly feed in landfills. Potential bacterial pathogens identified in faeces differed significantly between bird species, with higher relative abundance in gulls. Faeces from birds that feed in landfills (stork and gull) contained a significantly higher abundance of ARGs (sul1, blaTEM, and tetW). Genes conferring resistance to last resort antibiotics such as carbapenems (blaKPC) and colistin (mcr-1) were only observed in faeces from gulls. These results show that these bird species are reservoirs of antimicrobial resistant bacteria and suggest that waterbirds may disseminate antibiotic resistance across environments (e.g., from landfills to ricefields or water supplies), and thus constitute a risk for their further spread to wildlife and humans.

Long‐distance migrants vary migratory behaviour as much as short‐distance migrants: An individual‐level comparison from a seabird species with diverse migration strategies

As environmental conditions fluctuate across years, seasonal migrants must determine where and when to move without comprehensive knowledge of conditions beyond their current location. Animals can address this challenge by following cues in their local environment to vary behaviour in response to current conditions, or by moving based on learned or inherited experience of past conditions resulting in fixed behaviour across years.It is often claimed that long‐distance migrants are more fixed in their migratory behaviour because as distance between breeding and wintering areas increases, reliability of cues to predict distant and future conditions decreases. While supported by some population‐level studies, the influence of migration distance on behavioural variation is seldom examined on an individual level.Lesser black‐backed gulls Larus fuscus are generalist seabirds that use a diversity of migration strategies. Using high‐resolution multi‐year GPS tracking data from 82 individuals from eight colonies in Western Europe, we quantified inter‐ and intra‐individual variation in non‐breeding distributions, winter site fidelity, migration routes and timing of migration, with the objectives of determining how much variation lesser black‐backed gulls have in their migratory behaviour and examining whether variation changes with migration distance.We found that intra‐individual variation was significantly lower than variation between individuals for non‐breeding distributions, winter site fidelity, migration routes and timing of migration, resulting in consistent individual strategies for all behaviours examined. Yet, intra‐individual variation ranged widely among individuals (e.g. winter site overlap: 0–0.91 out of 1; migration timing: 0–192 days), and importantly, individual differences in variation were not related to migration distance.The apparent preference for maintaining a consistent strategy, present in even the shortest distance migrants, suggests that familiarity may be more advantageous than exactly tracking current environmental conditions. Yet, variation in behaviour across years was observed in many individuals and could be substantial. This suggests that individuals, irrespective of migration distance, have the capacity to adjust to current conditions within the broad confines of their individual strategies, and occasionally, even change their strategy.

Investigating avoidance and attraction responses in lesser black-backed gulls Larus fuscus to offshore wind farms

Movements through or use of offshore wind farms by seabirds while commuting or foraging may increase the potential for collision with turbine blades. Collision risk models provide a method for estimating potential impacts of wind farms on seabird populations, but are sensitive to input parameters, including avoidance rates (ARs). Refining understanding of avoidance through the use of high-resolution empirical movement data has the potential to inform assessments of the collision impacts of offshore wind farms on seabird populations. We assessed the movements of GPS-tagged lesser black-backed gulls Larus fuscus from a breeding colony in northwest England to estimate the species’ AR and avoidance/attraction index (AAI) to nearby offshore wind farms. To investigate both macro- (0-4 km) and meso-scale (0-200 m) responses to wind turbines, we used calculations of AR and AAI based on simulated vs. observed tracks. We found that birds exhibited an AR of -0.15 (95% CI: -0.44 to 0.06), indicating a degree of attraction within 4 km of the wind farms. However, AAI values varied with distance from wind farm boundaries, with a degree of avoidance displayed between 3 and 4 km, which weakened as distance bands approach wind farm boundaries. Meso-scale avoidance/attraction was assessed with regard to the nearest individual turbine, and flight height relative to the rotor height range (RHR) of the nearest turbine. We found attraction increased below the RHR at distances <70 m, while avoidance increased within the RHR at distances approaching the turbine. We explore how high-resolution tracking data can be used to improve our knowledge of L. fuscus avoidance/attraction behaviour to established wind farms, and so inform assessments of collision impacts.

High levels of fluoroalkyl substances and potential disruption of thyroid hormones in three gull species from South Western France

Per- and poly-fluoroalkyl substances (PFAS) raised increasing concerns over the past years due to their persistence and global distribution. Understanding their occurrence in the environment and their disruptive effect on the physiology of humans and wildlife remains a major challenge in ecotoxicological studies. Here, we investigate the occurrence of several carboxylic and sulfonic PFAS in 105 individuals of three seabird species (27 great black-backed gull Larus marinus; 44 lesser black-backed gull Larus fuscus graellsii; and 34 European herring gull Larus argentatus) from South western France. We further estimated the relationship between plasma concentrations of PFAS and i) the body condition of the birds and ii) plasma concentrations of thyroid hormone triiodothyronine (TT3). We found that great and lesser black-backed gulls from South Western France are exposed to PFAS levels comparable to highly contaminated species from other geographical areas, although major emission sources (i.e. related to industrial activities) are absent in the region. We additionally found that PFAS are negatively associated with the body condition of the birds in two of the studied species, and that these results are sex-dependent. Finally, we found positive associations between exposure to PFAS and TT3 in the great black-backed gull, suggesting a potential disrupting mechanism of PFAS exposure. Although only three years of data have been collected, we investigated PFAS trend over the study period, and found that great black-backed gulls document an increasing trend of plasma PFAS concentration from 2016 to 2018. Because PFAS might have detrimental effects on birds, French seabird populations should be monitored since an increase of PFAS exposure may impact on population viability both in the short- and long-term.

Predicting post-natal energy intake of lesser black-backed gull chicks by Dynamic Energy Budget modeling

The standard Dynamic Energy Budget (DEB) model is widely used to describe the physiology of individual animals. Here we parametrized the DEB model for the lesser black-backed gull Larus fuscus mainly on the basis of literature data. Next we performed an inverse modeling approach to predict the food intake rate of gull chicks (model input) on the basis of their growth trajectory from hatching to fledging (model output). Food intake rate and growth were also measured for this period in an aviary experiment, where three different diet treatments resulted in a large range in overall intake rate. These measured food intake rate data were not used in the parameter estimation procedure, but rather to validate model results. Model predictions of food intake rate were systematically only about 10% below the observations, but predictions and observations correlated strongly. The DEB model might be used to predict food provisioning rates in the field, which are difficult to obtain, on the basis of growth data, which are much easier to get.

High-resolution GPS tracking reveals sex differences in migratory behaviour and stopover habitat use in the Lesser Black-backed Gull Larus fuscus

Sex-, size- or age-dependent variation in migration strategies in birds is generally expected to reflect differences in competitive abilities. Theoretical and empirical studies thereby focus on differences in wintering areas, by which individuals may benefit from avoiding food competition during winter or ensuring an early return and access to prime nesting sites in spring. Here, we use GPS tracking to assess sex- and size-related variation in the spatial behaviour of adult Lesser Black-backed Gulls (Larus fuscus) throughout their annual cycle. We did not find sex- or size-dependent differences in wintering area or the timing of spring migration. Instead, sexual differences occurred prior to, and during, autumn migration, when females strongly focussed on agricultural areas. Females exhibited a more protracted autumn migration strategy, hence spent more time on stopover sites and arrived 15 days later at their wintering areas, than males. This shift in habitat use and protracted autumn migration coincided with the timing of moult, which overlaps with chick rearing and migration. Our results suggest that this overlap between energy-demanding activities may lead females to perform a more prolonged autumn migration, which results in spatiotemporal differences in foraging habitat use between the sexes.

Dodging the blades: new insights into three-dimensional space use of offshore wind farms by lesser black-backed gulls Larus fuscus

GPS telemetry is improving our understanding of the way animals interact with their environment. Recent research has used this technology to assess the impact of offshore wind farms (OWFs) on seabirds, but few studies have collected fine-scale data from birds flying within OWFs. We use GPS telemetry to investigate movements of lesser black-backed gulls Larus fuscus in relation to OWFs from a protected site with an active breeding colony. Individual birds varied considerably in their use of OWFs; 15 out of 24 birds visited them, and time spent in these areas was 1.3% of time budgets across all birds. Two birds, for which the most data was collected, frequently entered OWFs and flew at turbine blade height; however, their overlap with the spherical 3-dimensional rotor swept volume was significantly lower than a random distribution. Although preliminary, these tracking data suggest a lack of a macro-scale (wind farm-scale) avoidance for L. fuscus but a potential meso-scale (within wind farm-scale) avoidance of turbines. Such data are therefore important in improving our understanding of the implications of OWFs for seabirds.

Population trends and status of four seabird species (Uria aalge, Alca torda, Larus fuscus, Larus argentatus) at Stora Karlsö in the Baltic Sea

The island of Stora Karlsö hosts the largest colonies of fish-eating seabirds in the Baltic Sea. However, recent and reliable estimates of the number of breeding pairs of the main species have been missing. Based on a complete census in 2014, we estimated the number of Common Guillemots Uria aalge to 15,700 pairs, more than half (up to 70%) of the Baltic Sea population. The number has almost tripled since the early 1970s and the increase has been particularly strong the last 11 years, with an annual increase of 5.1%. We counted 24,600 individual adult Razorbills Alca torda and estimated it to correspond to a maximum of 12,300 pairs in 2015–2016 (census over two seasons). The colony has grown strongly; on average by 5.6% annually since the early 1970s, and Stora Karlsö now hosts up to 30% of the Baltic Sea population. Stora Karlsö also hosts colonies with about 300 pairs each of Lesser Black-backed Gull Larus fuscus and Herring Gull Larus argentatus. The gulls’ trends are negative, with an average annual decline the last 10-year period by 5.0% and 6.2%, respectively.

Offshore surprises: new at-sea bird records for Suriname (2013\u20132015)

Bird observations were collected from various types of survey vessels in Suriname’s territorial waters between 2013 and 2015. Dedicated, effort-related surveys were carried out from geophysical seismic survey vessels within an area located 80–110 km offshore (in 2013) and 165–290 km (in 2015). Opportunistic observations were recorded during fisheries surveys on a shrimp trawler operating along the 30 m depth contour, approximately 40–60 km offshore (in 2014). In total, 10 bird (sub-)species were observed during these surveys that previously were not recorded for Suriname, including Manx Shearwater Puffinus puffinus, Ruff Calidris pugnax, South Polar Skua Stercorarius maccormicki, Long-tailed Jaeger Stercorarius longicaudus, Sandwich Tern Thalasseus sandvicensis (ssp. acuflavidus), Roseate Tern Sterna dougallii, Bridled Tern Onychoprion anaethetus, Black Noddy Anous minutus, Scarlet Tanager Piranga olivacea and Black-and-white Warbler Mniotilta varia. In addition, Lesser Black-backed Gull Larus fuscus and Bulwer’s Petrel Bulweria bulwerii were photographed for the first time in Suriname. A Sooty Shearwater Ardenna grisea was recorded just outside the Exclusive Economic Zone (EEZ), and therefore does not count as a new country record. This paper contributes to a better understanding of the avifauna frequenting the waters off Suriname, which historically has been poorly studied. Most of the species reported here are migratory. The timing of our sightings therefore also helps in a better understanding of their at-sea distribution and migration patterns.