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Persistente polluenten zijn stoffen die traag afbreken en gedurende lange tijd (vaak decennia) in het milieu aanwezig blijven. Ze zijn meestal door de mens in het milieu gebracht, maar komen ook van nature in zeer lage concentraties in het milieu voor (bv. kwik). De productie en het gebruik van deze stoffen zijn al enkele tientallen jaren verboden in West- Europa. Persistente polluenten hopen zich via de voedselketen op in hogere organismen. Vooral in toppredators zoals zeevogels worden vaak relatief hoge concentraties gemeten.

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.

Since 2005, the Research Institute for Nature and Forest (INBO) performs monthly BACI-designed surveys to study seabird displacement following the construction of offshore wind farms in the Belgian part of the North Sea. For the first time since its completion in 2013 we report our findings for the C-Power wind farm at the Thorntonbank, and we also give an update of the results for the Bligh Bank wind farm after five years of post-impact monitoring.Compared to earlier reports and publications, we introduced some improvements in our modelling strategy. To correct for decreasing detectability with distance, the seabird numbers observed were now distance-corrected, and by allowing the detection functions to vary with wind force or wave height, temporal variation due to observation conditions was further reduced. We also included a fishery factor in the model, allowing to correct for the presence of beam trawlers in the vicinity of our survey tracks. As expected, this factor often explained a significant part of the variation in the counted numbers of gulls and northern fulmars.Based on the resulting impact models, we found significant avoidance by northern gannet and common guillemot at both sites. Common guillemot decreased in densities by 68% and 75% at the Thorntonbank and Bligh Bank respectively, and northern gannet by 99% and 82%. Razorbill decreased in numbers at the two sites, this decrease being significant at the Bligh Bank only (67%). Both sites attracted great black-backed gulls, this species having increased in numbers significantly by a factor 6.4 and 3.6 at the Thorntonbank and Bligh Bank respectively. The previously reported attraction effects of lesser black-backed gull and herring gull at the Bligh Bank were confirmed after two more years of monitoring, but no such effect was observed at the Thorntonbank. Finally, Sandwich tern appeared to be attracted to the offshore wind farm at the Thorntonbank, this effect being significant only for the buffer zone. This is in line with the results for the phase I of the Cpower wind farm when we also found attraction of Sandwich tern to the immediate surroundings of the six turbine wind farm.While the avoidance of common guillemot and northern gannet seems readily interpretable from a disturbance perspective, it is still difficult to pinpoint the observed increases in seabird numbers, even more so because these are not always consistent between both sites under study. Gaining more insight in the diurnal and tidal-dependent variation in numbers and behaviour of birds occurring inside the offshore wind farms seems indispensable for understanding the observed patterns and learning whether birds come to the wind farms merely for roosting and the related stepping stone function, or whether offshore wind farms also offer increased food availability. This should be investigated through oriented research making use of bird radar data, GPS tracking data of tagged gulls, fixed cameras and/or visual observations from a fixed location inside the wind farm.

Since 2005, the Research Institute for Nature and Forest (INBO) performs monthly BACI-designed surveys to study seabird displacement following the construction of offshore wind farms in the Belgian part of the North Sea. For the first time since its completion in 2013 we report our findings for the C-Power wind farm at the Thorntonbank, and we also give an update of the results for the Bligh Bank wind farm after five years of post-impact monitoring. Compared to earlier reports and publications, we introduced some improvements in our modelling strategy.

This report describes the fluctuations in the number of breeding pairs in the Special Protected Area under the Bird Directive ‘Kustbroedvogels te Zeebrugge-Heist’ and in the western port of Zeebrugge. These are by far the most important breeding sites for coastal breeders in Belgium and used to be of high importance for the biogeographical population as a whole. The quality of the breeding sites and the foraging areas is discussed and advice is given for a better management of the Special Protected Area.The populations of terns (Sandwich, Common and Little Tern) and Black-headed Gulls have decreased strongly since 2008 and the breeding success was insufficient for a stable population size. In Zeebrugge all 3 tern species used to exceed the threshold of 1% of their respective biogeographic population considerably. In 2014 none of the tern species reached this threshold. The decrease is due to persistent problems with land predators. Food availability seemed to play no role in this.Also some scarce species strongly declined in Zeebrugge. Crested Lark, Northern Wheatear, Mediterranean Gull and Yellow-legged Gull used to breed in the Zeebrugge port but in 2014 these species were no longer recorded. The numbers of Oystercatchers and Common Gull seem to have stabilised at a level much lower than before. Only the population of Common Ringed Plover is rather stable at about 8 pairs. Following a slight reduction in 2013, the populations of Herring and Lesser Black-backed Gulls further and strongly declined in 2014. Both species used to exceed the 1% level (maxima of 1.2 and 2.8%, respectively for Herring and Lesser Black-backed Gull), the number of Herring Gulls dropped to 0.2% of the total biogeographic population while that of Lesser Black-backed Gull dropped to 0.6%. This decline is due to disturbance by foxes and a decreased availability of suitable nesting areas.

Discards generated from marine fisheries have significantly affected species populations and community composition of seabirds through mechanisms such as competition, predator–prey interactions and nutrient transfer. Our understanding of the fate of discards beyond seabird scavenging is fragmented, but it is likely that similar mechanisms come into play. This study contributes in resolving this knowledge gap by quantifying the amount and composition of discards that become available to scavengers other than seabirds. The key was nevertheless found in revealing seabird discard consumption, as seabirds are likely the first in taking profit of fishery discards due to their high mobility. Their selective consumption determines the composition and amount of food remaining for others.The consumption of discards by scavenging seabirds was assessed for the French fishing fleet in the Bay of Biscay. Experimental sea trials were conducted to assess the proportion of discards consumed by foraging guild and discard type. Experimental discard consumption (EDC) was raised to fleet level by foraging guild using the total number of discards by discard type. The raising procedure accounted for the spatio-temporal variability of both foraging guilds and discards, by standardising both distributions to their lowest common resolution. Discards limited inferences in space, whilst the highest temporal resolution was determined by the biennial monitoring of foraging guilds. As EDC of roundfish by Large gulls and Gannets varied considerably, we investigated the main drivers. Consumption increased logarithmically with the number of ship followers for both guilds, but was greatly impaired by competitors for Large gulls. Competition between Large gulls and Gannets reduced the roundfish consumption by threefold, while other guilds such as Kittiwakes, Procellariids and Skuas had only a limited though significant influence. As Large gulls dominated during the first semester (April to September), the consumption of discards and notably roundfish was dictated by this foraging guild. The abundance of ship following Gannets was remarkably higher in the second semester (October to March). This change in flock composition and in numbers of ship followers implied an increase in the consumed proportion of roundfish of 27.9%. The total number of discards that became available to non-avian scavengers was however higher in the first semester, as more discards were produced during this period. Most discards comprised benthic invertebrates, but excluding this discard type revealed that over two thirds of the discards remained roundfish.

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."

Wind farms have three possible effects on birds. One of them is the barrier effect. Fox et al. (2006) and Krijgsveld et al. (2011) both described that birds change their direction of flight in the vicinity of a wind farm. It is unknown if this will also be the case for the offshore wind farms in the Belgian part of the North Sea and what the extent of this effect will be. To study the barrier effect there is a need for a technique that provides continuous data on a large scale. Automated radar systems offer such a tool. The objectives of this study are (1) to develop an analytical procedure to assess the quality of the radar data and to process the data to effectively remove noise (i.e. data reduction); (2) to develop and test a methodology for radar data analysis, including the influence of co-variables, such as wind direction; and (3) to draft the analytical procedure for future radar research in offshore wind farms (i.e. lessons learnt). The radar system was tested in the port of Zeebrugge, which holds in important tern breeding colony, to get acquainted with the system and the data processing. Foraging flights of terns are typically in a well-defined direction, as is the case for migrating birds. Therefore the foraging flights can be used as a proxy for the migration flights of migrating birds offshore. Variation in the direction of those foraging flights might be in function of co-variables such as wind direction and wind speed. The barrier effect created by offshore wind farms also makes migrating birds change their direction of flight when they approach a wind farm (Petersen et al., 2006; Krijgsveld et al., 2011). This is thus a co-variable that influences the direction of flight of migrating birds. Both parallels allow us using the data that were recorded near the tern colony as a proxy for the future offshore radar research. Lessons learnt will be directly applicable to the offshore work. The Zeebrugge case study offered a good opportunity to focus on a specific type of birds and flight behaviour with the radar system. A lot of experience was gained and the methodology was developed and fine-tuned for the future research offshore. It can be concluded that the radar system is an appropriate tool to monitor bird movements. It offers a possibility to show significant patterns in bird movements, even if that pattern is rather small.

At present, everybody agrees that offshore wind farms do impact the natural environment. Whether or not these impacts should be valued positive or negative, or ecologically and societally acceptable, however remains an open question. While boosting local species richness, the artificial hard substrata may for example also open the door to non-indigenous and even invasive species. Some fish and seabirds are further known to be attracted to wind farms, but fish do not necessarily take profit from these structures and seabirds may suffer from an increased collision risk. The true impact will therefore be valued only if local observations are up scaled to the ecoregion level.

Six years of monitoring triggered a reflection on how to best continue with the monitoring programme. The basic monitoring has to be rationalised at the level of the likelihood of impact detection, the meaningfulness of impact size and representativeness of the findings. Targeted monitoring should continue to disentangle processes behind the observed impact, for instance the overarching artificial reef effect created by wind farms. The major challenge however remains to achieve a reliable assessment of the cumulative impacts. Continuing consultation and collaboration within the Belgian offshore wind farm monitoring team and with foreign marine scientists and managers will ensure an optimisation of the future monitoring programme.

Studies of migration have revealed multiple trade-offs with other life-history traits that may underlie observed variation in migratory properties among ages and sexes. To assess whether, and to what extent, body size and/or sex-specific differences in competition for resources (e.g. breeding territories or winter food) may shape variation in migration distance and timing of arrival in ecologically and phylogenetically related species, we combined over 30 000 sightings of individually marked, sexually mature males and females of Herring Gulls Larus argentatus and Lesser Black-Backed Gulls Larus fuscus with biometric measurements and phenological observations at a mixed breeding colony. In L. argentatus, larger males migrated further from the breeding colony, whereas migration distance was independent of body size in adult females. In L. fuscus, no relationship between body size and migration distance was apparent in either sex. Mean arrival dates at the breeding colony did not vary with migration distances but differed between males and females of L. argentatus (but not L. fuscus). As allometry at least partly explains sexual segregation in migration behaviour in L. argentatus, but not in L. fuscus, we conclude that the effect of body size on sex-related migratory strategies may vary between closely related, sympatric species despite similar size dimorphism.

To categorize the marine environmental health status, the Oslo and Paris commissions have recently formulated Ecological Quality Objectives (EcoQOs) for many ecological features including the contamination of coastal bird eggs with mercury and organochlorines. In this study, we describe spatial and temporal patterns of egg contamination around the North Sea and compared them to the EcoQOs. Concentrations of mercury, polychlorinated biphenyl (SPCB) congeners, dichlorodiphenyltrichloroethane (SDDT) and derivatives, hexachlorobenzene (HCB) and hexachlorocyclohexane (SHCH) isomers were analysed in two tern species (Sterna hirundo and Sterna paradisaea) and Oystercatcher (Haematopus ostralegus) eggs collected between 2008 and 2010 in a total of 21 sites in seven countries surrounding the North Sea. Hg, SPCB and HCB were highest in the southern sites, while SDDT and SHCH concentrations were greatest in eggs from the western North Sea and the Elbe estuary. There were rarely any consistent decreases over time for any compounds. In the terns, Hg, HCB and SHCH increased at most sites, SPCB and SDDT in Sweden and Norway. In the Oystercatcher, HCB and SHCH increased at more than the half of the sites, SPCB, SDDT and Hg at several German sites. In the terns, Hg, SPCB and SDDT exceeded the EcoQO in all, HCB in most years and sites. At most sites, SHCH fulfilled the EcoQO in some study years. In the Oystercatcher, Hg, SPCB and SDDT exceeded the EcoQO in all or most years and sites. HCB and SHCH fulfilled the EcoQO in some or all years at most sites. The EcoQO was exceeded most frequently in estuaries. We conclude that EcoQOs are suitable for drawing contamination patterns of the coastal North Sea in an easily understandable manner, offering the opportunity to harmonize the EcoQOs with coordinated environmental monitoring programmes.

The abundance of plastics in stomachs of northern fulmars from the North Sea is used in the OSPAR Ecological Quality Objective (EcoQO) for marine litter. The preliminary EcoQO defines acceptable ecological quality as the situation where no more than 10% of fulmars exceed a critical level of 0.1 g of plastic in the stomach. During 2003–2007, 95% of 1295 fulmars sampled in the North Sea had plastic in the stomach (on average 35 pieces weighing 0.31 g) and the critical level of 0.1 g of plastic was exceeded by 58% of birds, with regional variations ranging from 48 to 78%. Long term data for the Netherlands since the 1980s show a decrease of industrial, but an increase of user plastics, with shipping and fisheries as the main sources. The EcoQO is now also used as an indicator for Good Environmental Status in the European Marine Strategy Framework Directive.

The Sandwich Tern Sterna sandvicensis is a Dutch Red List species with a population of 19,000 pairs in the Dutch coastal zone. It winters off the coasts of Africa and a small populations migrates into the Mediterranean or stays even more north.. In the Netherlands, breeding takes places in a small number of colonies in the Delta area and the Waddensea. In this study, Sandwich Terns from the Delta colony on the Scheelhoek (Natura 2000 SPA ‘Haringvliet’) were investigated which forage during the breeding season in Natura 2000 SPA ‘Voordelta’. In total 30 adult Sandwich Terns were equipped with radio transmitters, a colourring and a plumage colour (picrinic acid or silver nitrate solution). Thanks to these markings birds could be followed in the colonies, from airplanes and from the coast. Several birds used the sand banks off the coast of their breeding colonies to rest after the breeding season. After a short while they dispersed in western and northern direction with sightings in the northern part of the Netherlands (outside and within other colonies). These were always failed breeders, possibly scouting other colonies for future breeding places. Some of these birds even left the Dutch coasts and appeared in Scotland and Denmark. Adults with young probably dispersed into the North Sea after a short stay around the sand banks off the coast near the colonies. They probably head to more nutrient rich areas in the North Sea and adjacent areas where the young birds can practice their fishing techniques before they move south. The adults can build-up here good fat reserves before the start of migration. In September, most of the marked Sandwich Terns were south of their breeding places and during their southward migration birds were seen along the coast of France and on Lanzarote (Canary Islands). Our results showed that using markers on birds could yield good data with a resighting percentage of 20% within only one year. Furthermore, the use of plumage colouring proved to be a good method for obtaining information of individual birds as these colourings attract the attention of observers and are ‘readable’ over large distances.

In 2009, we refined the statistical set-up for the assessment of displacement effects on seabirds by wind farms in the Belgian part of the North Sea, more precisely at the Thorntonbank and Bligh Bank. The observed seabird densities were modelled through quasilikelihood estimation. The resulting models allowed to test for the difference in seabird occurrence between control and impact areas during the reference period. In case of Northern gannet, Sandwich tern, Common guillemot and Razorbill at the Thorntonbank, as well as for Northern gannet, Black-legged kittiwake and Common guillemot at the Bligh Bank, the delineated control area held highly similar densities compared to the impact area. This of course makes a good base for future BACI-comparison. Moreover, this modelling process is the first crucial step towards a power analysis, which will give insight in the probability of being able to statistically detect specified changes in bird numbers. In 2008, the first six turbines were installed at the Thorntonbank wind farm site. As expected, we were not yet able to discern any displacement effects. However, there are still about two hundred turbines to be installed at the Thorntonbank (C-Power), Bligh Bank (Belwind) and Bank Zonder Naam (Eldepasco), and as such it is too soon to draw any conclusions.

This is the fourth monitoring report of the Beached Bird Surveys along the Flemish coast. The study was conducted under the authority of the Flemish Government, Agency for Maritime and Coastal Services (AMDK-AK) and in close cooperation with the Flanders Marine Institute (VLIZ). This report presents the results of the Beached Bird Surveys conducted during the winter 2009/10. During the last winter remarkably low numbers of beached birds were found. In total 162 birds, 2 Harbour Porpoises and 1 Grey Seal were counted (Table 3). The density (expressed in numbers per km of beach) amounted to 0.36, which is the second lowest density since the onset of the surveys in 1961/62. Especially true seabirds such as auks, divers and seaducks were found in very low numbers. The numbers of Guillemots were even too low to compute a reliable index of the oil-rate. This coincided with low densities of most seabirds at sea. During the surveys it was also noted whether or not a bird was entangled in fishing gear or other plastic material. In this report we show some preliminary results regarding entanglement of seabirds. It shows that species are not equally sensitive to entanglement. Northern Gannets and Brent Geese were relatively often found entangled, followed by deep diving species (such as divers, grebes and auks) and most gull species.

In 2008, n.v. C-Power started up the construction of the first offshore wind farm at the Belgian Part of the North Sea (BPNS). This wind farm will be located on the shallows of the Thorntonbank, about fifteen nautical miles offshore. At the time of writing six windmills are erected of which two are in operation, but in the near future the wind farm will comprise of 60 turbines in total, each with a capacity of 5MW. Following the reference study (Vanermen et al. 2006), this report presents an update of the reference situation and the results of the year-1 monitoring of the avifauna at the Thorntonbank. To assess possible impacts on seabirds, we implement a methodology based on the BACI-principles. Hence the before-situation (2005-2007) is compared with the situation in 2008, during which the first construction works took place. Possible changes in avian densities are put in perspective by performing the same before-after comparison in a control area (see Vanermen et al. 2006).Based on intensive monitoring in 2005-2007, it seems that Annex I species Little gull, Sandwich tern and Common tern all occur in increased densities at the Thorntonbank wind farm site. On the other hand, Vanermen et al. (2006) overestimated the importance of the area to Great skuas. Next to this, we set up a ranking of seabird species according to their suitability for monitoring. Auks seems the most suitable species, followed by Little gull, Sandwich tern and Common tern. Hence, future monitoring will focus on these 5 species. A comparison of the monitoring results of the reference period (2005-2007) and the first construction year do not yet show clear effects.Meanwhile, n.v. Belwind has received their license for the construction and exploitation of a wind farm comprising of 110 3MW turbines on the Blighbank, 24 nautical miles offshore. Analogous to Vanermen et al. (2006), the Research Institute for Nature and Forest (INBO) carried out a reference study on the ornithological importance of the wind farm site at the BB, and selected a suitable control area.Based on intensive seabird monitoring, we know that the area is characterised by a typical offshore and relatively species-poor bird community. Black-legged kittiwakes and Common guillemots occur in high densities, while there are signs of increased densities of rarer species like Little gull and Great skua. As a control area, we selected an area including the rest of the Blighbank and the Oosthinderbank.Finally, we made a preliminary estimation of the number of collision victims at the future wind farm site at the Thorntonbank, based on flux counts, flying height observations and model calculations. Northern gannets and especially large gulls are most at risk. Meanwhile, this was an inventory of the needed (and lacking) parameters. It appears that radar research will be indispensable for determining data on bird movements, flying heights as well as avoidance behaviour.