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In 2022, highly pathogenic avian influenza (HPAI) A(H5N1) virus clade 2.3.4.4b became enzootic and caused mass mortality in Sandwich terns and other seabird species across northwestern Europe. We present data on characteristics of the spread of the virus between breeding colonies and the number of dead adult Sandwich terns recorded at breeding sites throughout northwestern Europe. Within two months after the first mortalities were reported, in total 20,531 adult Sandwich terns were found dead, which is >17% of the total northwestern European breeding population. Losses are likely higher, as we expect that many victims were not found (mortality rate might be up to 74% of the breeding population). Inside the colonies almost all chicks died. After the peak of the outbreak, in a colony established by late breeders, 25.7% of adults showed immunity against HPAI subtype H5. Removal of carcasses helped in reducing the spread of the disease and consequently total mortality. More research on the sources and modes of transmission, incubation times, effective containment and immunity is urgently needed to combat this major threat for colonial seabirds.

Colonial breeding provides benefits such as reduced predation risk, but also entails costs due to the enhanced levels of competition. In particular, it may require a significant amount of time and energy to establish a territory at the onset of reproduction, which in turn can impose carry-over effects on subsequent reproductive investments. Here we made use of GPS tracking devices to test how a colonial breeder, the lesser black-backed gull (Larus fuscus), balances its time investment between territorial and foraging activities throughout the pre-laying period, and investigated possible fitness consequences. As hypothesized, individuals that spent more time in their territories reduced their foraging time, foraged closer to the colony, and spent less time commuting during foraging trips. Although males initially invested more time in establishing a territory, both sexes gradually spent more time in their territory as the onset of egg laying, an energetically demanding period, approached. Furthermore, males that exhibited a higher territory attendance alleviated the females' time constraints for foraging and their partners laid larger eggs. Our results highlight the importance of quantifying carry-over effects related to time budgets during the (often understudied) pre-laying period, to better comprehend fitness consequences of colonial breeding.

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.

We use GPS tracking data on 28 adult Lesser Black-backed Gulls to show how these long-lived birds benefit from experience during migration. We found that stopover fidelity across years strongly depended on food source reliability. Birds using more reliable food sources thereby showed more consistent migratory behavior across years and covered significantly less distance while foraging during stopovers. There is a growing awareness that experience may play a major role in migratory decisions, especially in long-lived species. However, empirical support remains to date scarce. Here, we use multiyear GPS-tracking data on 28 adult Lesser Black-backed Gulls (Larus fuscus), a long-lived species for which migratory strategies typically consist of a series of long stopovers, to assess how experience affects interannual variation in stopover selection. We expect that food source reliability should play a pivotal role, as it both reduces the uncertainty on food availability across years, and enables for more efficient foraging during stopovers by reducing searching efforts. We found that during stopovers gulls indeed developed high fidelity to particular foraging locations, which strongly reduced the daily distance travelled for foraging. When revisiting stopovers in consecutive years, birds used over 80% of foraging locations from the previous year. Although the average fidelity to stopovers across years was a high as 85%, stopovers where birds showed high foraging site fidelity were up to 60% more likely to be revisited compared to stopover with low foraging site fidelity. Accordingly, birds using more stopovers with reliable foraging opportunities showed significantly less interannual variation in their stopover use than birds using stopovers with less reliable foraging opportunities. Our results thus highlight the need to further deepen our understanding of the role of cognitive processes in individual variation in migratory behavior.

Free-ranging animals are often used as bioindicators of both short- and long-term changes in ecosystem health, mainly to detect the presence and effects of contaminants. Birds, and gulls in particular, have been used as bioindicators over a broad range of marine and terrestrial ecosystems. In this study, we standardise the conditions for the use of a suite of biochemical markers in non-destructive matrices of Lesser Black-backed Gull (Larus fuscus) to facilitate future biomonitoring of marine and terrestrial contaminants. We characterized cholinesterase (ChE) in plasma and optimized assay conditions for ChE activity as a marker of neurotoxic damage. Moreover, we quantified variation in activity of ChE, lactate dehydrogenase (LDH), glutathione-S-transferase (GST) and catalase (CAT) as well as variation ranges of lipid peroxidation (LPO), in free-ranging adults and captive chicks. The main ChE form present in plasma of both adults and chicks was butyrylcholinesterase (BChE) followed by acetylcholinesterase (AChE), whose relative proportion in plasma tended to decrease with increased chick age. LPO levels and GST activity in blood cells (BCs) decreased significantly with increasing chick age, while BChE and LDH activity in plasma were not age-dependent. CAT in BCs tended to decline non-significantly in older chicks. Results of this study underscore the importance of standardising assay conditions and assessing intrinsic baseline variation in biochemical markers, before biochemical quantification. Data presented here provide a foundation for future use of BChE and LDH activity in plasma, as well as oxidative stress markers (LPO, CAT and GST) in BCs, to monitor environmental stress effects in Lesser Black-backed gulls.

While competition is generally presumed to promote intraspecific niche diversification, populations of many apparent generalist species still exhibit considerable individual variation in foraging specialization. This suggests that different cost-benefit trade-offs may underlie individual variation in foraging specialization. Indeed, while specialization may improve foraging efficiency by a better knowledge of the spatio-temporal availability of resources, individuals may also become more vulnerable to fluctuations in these resources. In this study, we used multiyear GPS tracking data of 19 Herring Gulls (Larus argentatus) breeding along the Belgian coast to assess whether foraging effort and reproductive success varied among different levels of foraging specialization. First, we quantified spatial and habitat specialization during incubation and chick rearing for 31 individual breeding cycles during which birds raised young until the age of 21 days. Next, we tested whether spatial and habitat specialization were related to the daily distance covered (as a proxy for foraging effort), and to chick growth (as a proxy for reproductive success). We found that birds primarily varied in their extent of habitat specialization. Habitat specialization was associated with reduced daily distances covered and increased offspring growth rates, in particular the growth rate of the youngest chicks. Yet, positive effects of habitat specialization on chick growth decreased at high levels of spatial specialization. Our results thus demonstrate fitness benefits of foraging specialization during our 5-year study period, but also highlight the need for longer-term studies as environmental changes may cause benefits to vary throughout a lifetime. GPS tracking reveals that specialization reduces foraging effort and increases the breeding success of Belgian Herring Gulls.

Background Parental care benefits the offspring, but comes at a cost for each parent, which in biparental species gives rise to a conflict between partners regarding the within-pair distribution of care. Pair members could avoid exploitation by efficiently keeping track of each other’s efforts and coordinating their efforts. Parents may, therefore, space their presence at the nest, which could also allow for permanent protection of the offspring. Additionally, they may respond to their partner’s previous investment by co-adjusting their efforts on a trip-to-trip basis, resulting in overall similar parental activities within pairs. Methods We investigated the coordination of parental care measured as nest attendance and foraging effort in the Lesser black-backed gull (Larus fuscus), a species with long nest bouts that performs extended foraging trips out of sight of their partner. This was achieved by GPS-tracking both pair members simultaneously during the entire chick rearing period. Results We found that the timing of foraging trips (and hence nest attendance) was coordinated within gull pairs, as individuals left the colony only after their partner had returned. Parents did not match their partner’s investment by actively co-adjusting their foraging efforts on a trip-by-trip basis. Yet, pair members were similar in their temporal and energetic investments during chick rearing. Conclusion Balanced investment levels over a longer time frame suggest that a coordination of effort may not require permanent co-adjustment of the levels of care on a trip-to-trip basis, but may instead rather take place at an earlier stage in the reproductive attempt, or over integrated longer time intervals. Identifying the drivers and underlying processes of coordination will be one of the next necessary steps to fully understand parental cooperation in long-lived species.

Research on the space use and behaviour of waterbirds yields important insights on human-wildlife interactions of ecological and societal importance under global change. The extent to which dynamic (within-season) changes in anthropogenic landscapes affect these interactions is poorly understood. Lesser Black-backed Gulls (Larus fuscus) are prominent bio-vectors of biological, synthetic and inorganic materials, and have exhibited large increases in abundance in parts of southern Europe in recent decades. We combined GPS tracking, earth observation, accelerometry and field observations to study the space use of overwintering gulls in a mixed rice field landscape in Andalusia, Southern Spain. We used Manly selectivity metrics, a common quantitative measurement of habitat selection, and classified remote sensing imagery to directly evaluate space use and habitat selection for these gulls and how it changed throughout the rice harvest cycle. Analysis of over 45,000 GPS fixes and 14 classified remotely-sensed images from winter 2016-17 showed dynamic space use driven by the harvest-related flooding across the rice harvest cycle. Prior to harvest, gulls foraged in rice paddies during the day and roosted in adjacent waterbodies (the River Guadalquivir, and fish ponds) at night. During harvest, they spent nearly 100% of their daily cycle within the rice fields, foraging in harvested paddies and roosting in post-harvest, flooded paddies. After harvest, they roosted in flooded paddies at night and foraged at landfills in the surrounding landscape. Gull space use at landscape and paddy scales was closely linked to dynamic land and water management over the rice agricultural cycle, illustrating how human activities influence the movements of ecologically important, human-associated bio-vectors like gulls. The frequent early-spring movement patterns of gulls between landfills and agricultural fields makes them an important bio-transport link for potentially toxic materials and pathogens between waste sites and places where food is grown for human consumption.

Background: Research on the space use and behavior of waterbirds—as highly mobile of wetland habitats—yields important insights on human-wildlife interactions of ecological and societal importance under global change. The extent to which dynamic (within-season) changes in anthropogenic landscapes affects these interactions is poorly understood. Lesser black-backed gulls (Larus fuscus) are prominent biovectors of biological and artificial materials, and have exhibited large population increases in parts of southern Europe in recent decades. Methods: We combined GPS tracking, earth observation, accelerometry and field observations to study the space use of overwintering in a mixed rice field landscape in Andalusia, Southern Spain. We used Manly selectivity metrics and classified remote sensing imagery to directly evaluate space use and habitat selection for these gulls and how it changed throughout the rice harvest cycle. Results: Analysis of over 45,000 GPS fixes and 14 classified remotely-sensed images from winter 2016-17 showed dynamic space use driven by the harvest-related flooding across the rice harvest cycle. Prior to harvest, gulls foraged in rice paddies during the day and roosted in adjacent waterbodies (the River Guadalquivir, and fish ponds) at night. During harvest, they spent nearly 100% of their daily cycle within the rice fields, foraging in harvested paddies and roosting in post-harvest, flooded paddies. After harvest, they roosted in flooded fields at night and foraged at landfills in the surrounding landscape. Conclusion: Gull space use at landscape and paddy scales was closely linked to dynamic land and water management over the rice agricultural cycle, illustrating the detailed scales at which human activities influence the movements of ecologically important, human-associated biovectors like gulls. The frequent early-spring movement patterns of these increasingly numerous gulls between landfills and agricultural fields an important biotransport link for potentially toxic materials between waste sites and places where food is grown for human consumption.

17 pages, 7 tables, 5 figures, Distribution maps of cetaceans and seabirds at basin and monthly scales are needed for conservation and marine management. These are usually created from standardized and systematic aerial and vessel surveys, with recorded animal densities interpolated across study areas. However, distribution maps at basin and monthly scales have previously not been possible because individual surveys have restricted spatial and temporal coverage. This study develops an alternative approach consisting of: (a) collating diverse survey data to maximize spatial and temporal coverage, (b) using detection functions to estimate variation in the surface area covered (km2) among these surveys, standardizing measurements of effort and animal densities, and (c) developing species distribution models (SDM) that overcome issues with heterogeneous and uneven coverage. 2.68 million km of survey data in the North‐East Atlantic between 1980 and 2018 were collated and standardized. SDM using Generalized Linear Models and General Estimating Equations in a hurdle approach were developed. Distribution maps were then created for 12 cetacean and 12 seabird species at 10 km and monthly resolution. Qualitative and quantitative assessment indicated good model performance. Synthesis and applications. This study provides the largest ever collation and standardization of diverse survey data for cetaceans and seabirds, and the most comprehensive distribution maps of these taxa in the North‐East Atlantic. These distribution maps have numerous applications including the identification of important areas needing protection, and the quantification of overlap between vulnerable species and anthropogenic activities. This study demonstrates how the analysis of existing and diverse survey data can meet conservation and marine management needs, JJW, PGHE, JGH and SW are supported through the NERC/DEFRA funded Marine Ecosystems Research Programme (MERP: NE/L003201/1).

Current emission and mobilization rates of mercury (Hg) in the environment pose extensive threats to both wildlife and human health. Assessing the exposure risk and effects of Hg contamination in model species such as seabirds is essential to understand Hg risks at the population and ecosystem levels. The lesser black-backed gull (Larus fuscus), a generalist seabird species, is an excellent model species because it forages in both marine and terrestrial habitats, which in turn differ in their Hg exposure risk. To identify possible deleterious effects of Hg exposure on developingL. fuscuschicks, a dietary experiment was carried out and chicks were provided a marine, terrestrial, or mixed diet. The effects of embryonic and dietary Hg exposure on chick body condition and physiological state were assessed at different developmental stages until fledging age (30 d). Overall physiological condition was lower in chicks fed a predominantly marine diet, which coincided with higher Hg loads in blood and primary feathers. However, no effect of dietary uptake of Hg was observed on body condition or in terms of genotoxic damage. Body condition and genotoxic damage correlated instead with Hg exposure during embryonic development, which seems to indicate that embryonic exposure to Hg may result in carry-over effects on later chick development.Environ Toxicol Chem2020;39:2008-2017. (c) 2020 SETAC

Species breeding in urban environments are highly prone to a wide variety of non-natural, human activities, which range from short-term disturbances to the degradation or loss of suitable habitat. The latter in turn may force individuals to relocate to new sites for foraging or breeding, both of which presumably entails fitness costs due the trade-offs of finding and exploring new habitats. Species showing a high level of spatial foraging specialisation or nest site fidelity are expected to be most vulnerable. In this study, we explored the consequences of nest site loss on the reproductive investment of lesser black-backed gulls (Larus fuscus), a site faithful seabird species breeding in an urban environment. We monitored a population of 1.173 colour-ringed gulls across 13 years, that involved several episodes of spatially restricted loss of breeding habitat. We found that birds which lost their breeding territories reduced their investment into the eggs as reflected in a decrease of the clutch volume. They relocated over larger distances compared to birds that relocated voluntarily. Moreover, the likelihood of skipping the subsequent breeding season increased after a forced relocation. These negative effects of forced relocation likely contribute to the decline in the number of breeding pairs in our urban population as observed during the last ten years, and highlights the importance of maintaining a stable breeding environment in urban areas for the conservation of this and potentially other colonial breeding seabird species.

In 2006 is een planologische kernbeslissing genomen over het Project Mainportontwikkeling Rotterdam (PMR). In dit kader is in 2008 begonnen met de aanleg van Maasvlakte 2. In samenhang daarmee zijn natuurcompensatiemaatregelen genomen in de Voordelta. Vanaf 2009 is in het kader van het project Natuurcompensatie Voordelta (PMR-NCV) een monitoring- en onderzoeksprogramma uitgevoerd in de Voordelta, voortvloeiend uit de monitoringverplichtingen in het kader van de vergunning op grond van de Nb-wet 1998 voor de aanleg en aanwezigheid van Maasvlakte 2 en de bijbehorende natuurcompensatie. Het hier voorliggende rapport vormt de wetenschappelijke rapportage over de resultaten van het programma. Het rapport geeft een synthese van de monitorings- en onderzoeksresultaten uit de nulmetingen (2004-2007) en de eerste (2009-2015) en tweede (2016-2018) fase van PMR-NCV, aangevuld met de resultaten van ander relevant onderzoek. Op grond hiervan worden de effecten van de natuurcompensatiemaatregelen beschreven. Dit rapport vormt een vervolg op de in 2018 gepubliceerde synthese (Tulp et al., 2018a). Het rapport omvat zowel een actualisatie van analyseresultaten en conclusies op basis van meetgegevens uit recente jaren die nog niet beschikbaar waren in 2018, als resultaten van nieuwe analyses.

Background Habitat loss can force animals to relocate to new areas, where they would need to adjust to an unfamiliar resource landscape and find new breeding sites. Relocation may be costly and could compromise reproduction. Methods Here, we explored how the Lesser black-backed gull (Larus fuscus), a colonial breeding seabird species with a wide ecological niche, responds to the loss of its breeding habitat. We investigated how individuals adjusted their foraging behaviour after relocating to another colony due to breeding site destruction, and whether there were any reproductive consequences in the first years after relocation. To this end, we compared offspring growth between resident individuals and individuals that recently relocated to the same colony due to breeding habitat loss. Using GPS-tracking, we further investigated the foraging behaviour of resident individuals in both colonies, as well as that of relocated individuals, as enhanced foraging effort could represent a potential driver of reproductive costs. Results We found negative consequences of relocation for offspring development, which were apparent when brood demand was experimentally increased. Recently relocated gulls travelled further distances for foraging than residents, as they often visited more distant foraging sites used by residents breeding in their natal colony as well as new areas outside the home range of the residents in the colony where they settled. Conclusions Our results imply that relocated individuals did not yet optimally adapt to the new food landscape, which was unexpected, given the social information on foraging locations that may have been available from resident neighbours in their new breeding colony. Even though the short-term reproductive costs were comparatively low, we show that generalist species, such as the Lesser black-backed gull, may be more vulnerable to habitat loss than expected. Long term studies are needed to investigate how long individuals are affected by their relocation in order to better assess potential population effects of (breeding) habitat loss.

Background Animals can obtain a higher foraging yield by optimizing energy expenditure or minimizing time costs. In this study, we assessed how individual variation in the relative use of marine and terrestrial foraging habitats relates to differences in the energy and time investments of an avian generalistic feeder (the Lesser Black-backed Gull, Larus fuscus), and how this changes during the course of the chick-rearing period. Methods We analyzed 5 years of GPS tracking data collected at the colony of Zeebrugge (Belgium). Cost proxies for energy expenditure (overall dynamic body acceleration) and time costs (trip durations and time spent away from the colony), together with trip frequency, were analyzed against the relative use of the marine and terrestrial habitats. Results The marine habitat was most often used by males and outside weekends, when fisheries are active. Marine trips implied higher energetic costs and lower time investments. As chicks became older, terrestrial trips became more prevalent, and trip frequency reached a peak towards 20 days after hatching of the first egg. Over a full chick rearing period, energy costs varied widely between individuals, but no trends were found across the marine foraging gradient. Conversely, a higher use of marine foraging implied lower overall amounts of time spent away from the colony. Conclusions Foraging habitat choice was related to overall time costs incurred by gulls, but not to energy costs. The effect of chick age on foraging habitat choice and effort may be driven by energy expenditure constraints on the amount of marine foraging that can be performed. If time is less constraining to them, Lesser Black-backed Gulls may meet the increasing chick demand for food by switching from high to low energy demanding foraging strategies.

Eutrophication of aquatic ecosystems is a global problem with major ecological and economic impacts. In many lakes and reservoirs, guanotrophication occurs when roosting waterbirds import nutrients (nitrogen and phosphorus) from surrounding terrestrial habitats. To date, nutrient loading by waterbirds has been estimated based on censuses in the absence of detailed information on their movements. We quantified nutrient importation by the lesser black-backed gull (Larus fuscus) to Fuente de Piedra (1,350 ha) in Andalusia (south-west Spain), where an average of 36,288 individuals are counted in January. During seven winters from 2010 to 2017, we used movement data from 20 individual gulls tagged with Global Positioning System trackers that foraged in four landfills. Together with monthly bird counts and measurements of total N and P content in faeces and pellet samples, movement data were used to quantify the total external loading effect for different winters. Movement data allowed us to quantify the proportion of time spent in the lake and the time spent at different foraging sites and enabled correction of censuses. According to tracking data, on average 69% of the birds had already left the lake to head for feeding sites when waterbird counts were carried out. Nutrient inputs to the lake depend partly on the proportion of the day that gulls spend there, which was higher in late winters and was reduced when lake depth went below or above 20–35 cm. An estimated average of 10.17 kg N ha−1 year−1 and 2.07 kg P ha−1 year−1 were imported to this closed-basin lake by gulls each winter, with highest values recorded in winter 2016–2017. Gull guano is the most important winter source of nutrients to the lake. Regurgitated pellets have been ignored as a source of nutrients in other guanotrophy studies, but we found them to be a more important source of P than faeces. A movement ecology approach complements traditional censuses and facilitates the study of guanotrophication in multiple ways, including identification of sources of nutrients, correction of censuses, and measuring time spent at roost sites., V.M.V. was supported by a PhD contract from Programa Internacional de Becas La Caixa-Severo Ochoa 2016. Lesser black-backed gull count data and FP water levels were provided by the Programa de Emergencias, Control Epidemiológico y Seguimiento de Fauna Silvestre de Andalucía, Consejería de Medio Ambiente y Ordenación del Territorio of Junta de Andalucía, Spain. We thank M. Rendón for his help in the field and him, J. Aguilar Amat and G. Batanero for their useful comments. Part of this work was supported by data and infrastructure provided by INBO and VLIZ as part of the Flemish contribution to the LifeWatch observatory funded by FWO. The UvA-Bits tracking studies are facilitated by infrastructures for e-Science, developed with support of the NLeSC (http://www.esciencecenter.com/) and LifeWatch, carried out on the Dutch national e-infrastructure with support from the SURF Foundation. The data are held jointly by the BTO, University of Amsterdam, NIOZ, INBO and the funders of the project, and can be made available through their agreement. This work complied with Dutch law regarding ethical matters (#DEC-KNAW CL07.03). For birds in the U.K., tagging was undertaken under licence and approved by the independent Special Methods Technical Panel of the U.K. Ringing Scheme. This research was supported by Spanish National Plan project CGL2016-76067-P (AEI/FEDER, EU).

Human-mediated food sources offer possibilities for novel foraging strategies by opportunistic species. Yet, relative costs and benefits of alternative foraging strategies vary with the abundance, accessibility, predictability and nutritional value of anthropogenic food sources. The extent to which such strategies may ultimately alter fitness, can have important consequences for long-term population dynamics. Here, we studied the relationships between parental diet and early development in free-ranging, cross-fostered chicks and in captive-held, hand-raised chicks of Lesser Black-backed Gulls (Larus fuscus) breeding along the Belgian coast. This traditionally marine and intertidal foraging species is now increasingly taking advantage of human activities by foraging on terrestrial food sources in agricultural and urban environments. In accordance with such behavior, the proportion of terrestrial food in the diet of free-ranging chicks ranged between 4% and 80%, and consistent stable isotope signatures between age classes indicated that this variation was mainly due to between-parent variation in feeding strategies. A stronger terrestrial food signature in free-ranging chicks corresponded with slower chick development. However, no consistent differences in chick development were found when contrasting terrestrial and marine diets were provided ad libitum to hand-raised chicks. Results of this study hence suggest that terrestrial diets may lower reproductive success due to limitations in food quantity, rather than quality. Recent foraging niche expansion toward terrestrial resources may thus constitute a suboptimal alternative strategy to marine foraging for breeding Lesser Black-backed Gulls during the chick-rearing period.

The work at Wageningen Marine Research for this publication was partially funded by RijksWaterstaat (RWS) of the Netherlands Ministry of Infrastructure and Water Management as a document to support future policy decision making. Monitoring plastic in stomachs of beached northern fulmars for OSPAR's Ecological Quality Objectives (EcoQOs) has been incorporated into the European Marine Strategy Framework Directive (MSFD). This paper aims to provide the appropriate tools to interpret the monitoring results. MSFD requires a data-derived threshold value (Fulmar-TV) representing ‘Good Environmental Status’. Such Fulmar-TV was calculated from near-pristine Canadian Arctic data where 10.06% of fulmars exceeded the level of 0.1 g ingested plastic. This Fulmar-TV is almost identical to the earlier OSPAR EcoQO, arbitrarily set at 10%. The MSFD approach was evaluated for 2661 North Sea fulmars in 2002–2018. Between 2014 and 2018, 51% of 393 fulmars exceeded 0.1 g plastic, significantly above the proposed Fulmar-TV. Linear regression of individual ingested plastic mass over the 2009–2018 period indicates a significant decrease. Over the longer term 2002–2018, logistic regression of annual EcoQ% shows a significant decline and predicts compliance with the Fulmar-TV by 2054. Publisher PDF

The diet of seabirds can yield important insights into the status of economically and ecologically important fish. By analyzing the otoliths found in the birds’ droppings, researchers can observe which fish the birds eat in which abundances. However, identifying the species based on an otolith image is quite labor-intensive and requires particular expertise. In this work, we show that a deep convolutional neural network can identify six fish species with high accuracy. We show that this deep learning approach outperforms more traditional methods and is also more accessible to set up in practice. By exploiting the hierarchy in the species labels, we impose a structure on the prediction probabilities, leading to a remarkable improvement compared to a conventional artificial neural network. Importantly, we can attain good results using only a modest dataset, demonstrating that such approaches are feasible for small-scale and specialized projects.

Fishery discards subsidise the food supply of a large community of scavenging seabirds, thus substantially influencing seabird ecology. Seabird preference for certain types of discards determines the number and composition of discards available for non-avian marine scavengers. To quantify both portions of discards temporally as well as spatially, we have used a modelling framework that integrates the spatial and temporal variation in seabird distribution, seabird attraction to fishing vessels, and discard distribution. The framework was applied to a case study in the Bay of Biscay, where a wide variation in discard consumption was observed across seabird foraging guilds, discard types, periods, and locations. Seabirds removed about one-quarter of the Bay of Biscay discards. The remaining sinking discards have limited potential to subsidize scavenging benthic communities on a large scale, but they may contribute substantially to scavenger diets on a local scale. Changes in food subsidies caused by discard mitigation measures, such as the “landing obligation” in the European Common Fisheries Policy, are likely to have ecosystem effects on both scavenging seabirds and non-avian marine scavengers.

Tracking devices are increasingly used to monitor individual movement patterns continuously and in high resolution. However, carrying a device could potentially compromise an individual's physiology or behaviour, thereby making tracking data unreliable for detailed behavioural measurements. To this end, we assessed the possible consequences of the application of GPS devices on offspring development in an opportunistic seabird species, the lesser black-backed gull (Larus fuscus), by comparing the growth and survival of nestlings of which none, one or both parents were equipped with a GPS device. We found that the developmental trajectories of the nestlings were not affected, and there were no differences in skeletal size and body mass at the fledging stage. A lack of negative effects on offspring development strongly suggests that the parental behaviour, and thus likely the foraging behaviour, did not differ between tagged and non-tagged individuals. The evidence that GPS data can be used to reliably study parental care, as well as other aspects of the bird's behaviour, opens up new possibilities to study behavioural and evolutionary ecological questions in ever-increasing resolution.

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.

Seabirds exhibit considerable behavioural flexibility in foraging investment in order to meet the nutritional needs of their chicks during variable environmental conditions. Although regulation of offspring provisioning is generally thought to be related to species-specific constraints imposed by central place foraging, some studies suggest different responses within the same species linked to local differences in foraging conditions. Under adverse conditions, seabirds are expected to be less flexible because they must secure their own survival chances first before investing in current reproduction. Short-ranging single-prey loaders are expected to show large intra-specific variation in time spent on foraging because their mode of foraging is energetically expensive, and because they face restricted possibilities to increase the numerical prey input to the colony compared to multiple prey loaders. In this study, we examined if and how the single-prey loading Sandwich Tern Thalasseus sandvicensis varies colony attendance based on the nutritional status of their chick as well as parental body condition in two study colonies. The proportion of time that a chick was left unattended at the colony negatively correlated with chick body condition, suggesting that the parents tried to counterbalance poor feeding conditions by investing more time in foraging. Energy transport rates to the chicks (corrected for time spent away from the colony) and body condition of the chicks were similar in both colonies. However, at Zeebrugge, where adults were in poor body condition, parental non-attendance was much lower than on Griend, even when chicks were in poor condition. Still, our results suggest that parental nest non-attendance in Sandwich Terns is merely a corrective response to food loss to kleptoparasitic gulls in order to meet the nutritional status of the chick, although an effect of adult body condition could not be excluded.

The diet of terns is often considered indicative for the availability of prey or shifts in prey communities. So far, most studies focused on the chick diet. Here we study the diet of breeding adult Sandwich terns based on faecal samples collected in five different colonies in Belgium and the Netherlands in 2007–2015. Breeding adult Sandwich terns in the study area proved to be very specialistic with only three prey types frequently found in their diet. Clupeidae were the most abundant fraction by number, making up 40 to 70% of the diet in most years. The clupeid fraction almost exclusively consisted of relatively small (< 95 mm) Herring Clupea harengus and Sprat Sprattus sprattus. Ammodytidae accounted for another 20 to 60% of the diet composition, 80–140 mm being the most common length class. In all years jaws of Nereididae were found in the diet with up to 57% of the total diet consisting of Nereis-worms. We show that there is a clear link between the adult diet of Sandwich terns and the ecology of the involved prey species. Also, differences in both species composition and mean length of the prey species between colonies in the same year were much smaller than the differences between years. We therefore argue that the diet of adult Sandwich terns might prove a cheap and good indicator for the availability of small pelagic fish species.

In several species of birds, migration strategies may differ greatly even within a single population. Migration is often assumed to be a costly endeavour, especially for long distance migrants and these costs are presumablycompensated for by better survival conditions in the non-breeding area. One way to assess the cost of alternative strategies is to study the investment in movement within the context of the entire annual cycle. In this study wecompare trade-offs associated with several migration strategies in a generalist seabird. We used GPS tracking data to quantify lesser black-backed gulls’ movement throughout their annual cycle. The annual cumulativedistance travelled by long distance migrants wintering in west Africa, thousands of kilometres from their breeding colony, did not differ significantly from individuals of the same breeding colony wintering only a few hundred kilometres away. Within a year, birds travelled approximately 30,000 km across all migrations strategies. Short distance migrants returned earlier than long distance migrants. Maximum range, cumulative distance travelled or timing of arrival at the breeding area were not correlated with sex and wing length. Individuals spent only a small proportion of their time in flight and generally spent < 20% of their time at sea throughout an annual cycle, suggesting a reliance on inland resources for many individuals. Studying movement throughout the annual cycle may change our perspective when considering the consequences of different migration strategies. In several species of birds, migration strategies may differ greatly even within a single population. Migration is often assumed to be a costly endeavour, especially for long distance migrants and these costs are presumably compensated for by better survival conditions in the non-breeding area. One way to assess the cost of alternative strategies is to study the investment in movement within the context of the entire annual cycle. In this study we compare trade-offs associated with several migration strategies in a generalist seabird. We used GPS tracking data to quantify lesser black-backed gulls’ movement throughout their annual cycle. The annual cumulative distance travelled by long distance migrants wintering in west Africa, thousands of kilometres from their breeding colony, did not differ significantly from individuals of the same breeding colony wintering only a few hundred kilometres away. Within a year, birds travelled approximately 30,000 km across all migrations strategies. Short distance migrants returned earlier than long distance migrants. Maximum range, cumulative distance travelled or timing of arrival at the breeding area were not correlated with sex and wing length. Individuals spent only a small proportion of their time in flight and generally spent < 20% of their time at sea throughout an annual cycle, suggesting a reliance on inland resources for many individuals. Studying movement throughout the annual cycle may change our perspective when considering the consequences of different migration strategies.

Generalist species can potentially exploit a wide variety of resources, but at the individual level they often show a certain degree of foraging specialization. Specific foraging strategies, however, may increase exposure to environmental contaminants that can alter the cost-benefit balance of consuming particular food items. The Lesser Black-backed Gull (Larus fuscus) is known to opportunistically feed on a wide range of marine and terrestrial prey that differ in contaminant load, such as mercury (Hg) that strongly biomagnifies through the aquatic food web. The hypothesis tested in this study were: i) a predominant use of marine prey by females during egg-formation and by both parents during chick rearing increases the exposure to Hg during embryonic development and chick growth, and ii) this affects parental investment in clutch volume, chick growth and body condition. Total Hg burden and isotopic signatures of carbon (delta C-13) and nitrogen (delta N-15) were determined for eggs, down feathers, and primary feathers of L. fuscus chicks collected at a coastal colony in Belgium. As expected, eggs and feathers of chicks from parents with a stable isotope signature that suggested a predominantly marine diet had higher levels of Hg. The use of marine resources by females during the egg-formation period positively correlated to maternal investment in egg size, though entailing the cost of increased Hg-concentrations which in turn negatively affected clutch volume. Furthermore, it is shown that the use of chick down feathers is a suitable matrix to non-lethally estimate Hg concentrations in eggs. Contrary to our expectations, no relationship between Hg exposure and chick growth or chick body condition was found, which may be due the low concentrations found. We conclude that currently Hg contamination does not constitute a risk for development and condition of L. fuscus offspring at the levels currently observed at the Belgian coast. (C) 2017 Elsevier B.V. All rights reserved.

Capsule Multiple tracking methods (colour-rings, plumage-markings and GPS-loggers) revealed that adult Sandwich Terns Thalasseus sandvicensis from the Netherlands showed prospecting behaviour in other colonies within Northwest Europe. Birds were recorded from a few kilometres to over 850 km away and in different countries around the Southern North Sea. Our data suggest large-scale connectivity between Northwest European Sandwich Tern colonies. Such connectivity is potentially of great importance when modelling the population structure of this species.

The Belgian coastal zone hosts a complex of space-use and resource-use activities with a myriad of pressures. Specifically at the beaches, predictions on sea-level rise, storms and flood risk from the North Sea have led to several big coastal defence projects. Management of sandy beaches is a multi-faceted and complex endeavor, where the interests of several stakeholders need to be combined.In this paper, we used the marine biological valuation (BV) method in order to (1) analyse the spatial structure of the intertidal and shallow subtidal Belgian coastal zone; and (2) explore the applications of BV for an ecosystem-based approach to marine spatial planning of two space-use conflicts at the Belgian coast, being flood protection, by means of beach nourishment, and nature conservation.The biological value was assessed with a focus on a detailed and integrated dataset (1995 – 2011), gathering all available ecological information on macrobenthos, epibenthos, hyperbenthos and birds. The 67 km Belgian coastline was divided into an across-shore intertidal and shallow subtidal subzone while the width of the along-shore subzones comprises 250 m for benthic components and wider distances of 3 km for the birds. The intrinsic biological value of each subzone was calculated using the BV method and the pertained score, ranging from very low to very high, was plotted accordingly in order to obtain a marine biological valuation map (BVM).Following trends in BV along the Belgian coastline were detected: (1) a strong mosaic pattern of BV along the coastline; (2) a clear lack of (benthic) data at the eastern part of the Belgian coast; (3) a rather high biological value score for around 70 % of the shallow part of the subzones, compared with the intertidal part; (4) a high/very high biological values found in intertidal zones located immediately to the east of the harbours Nieuwpoort, Oostende and Zeebrugge.A detailed analysis of protected areas and areas under coastal flood risk indicates that the use of BVMs is very promising in order to differentiate between several impact values. BV can therefore be used as a management tool by local decision makers and can allow for the integration of ‘natural/ecological values’ at an early stage of policy implementation.

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).