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The cuneiform southernmost part of the North Sea is an important corridor for seabird migration. An estimated total of 1-1.3 million seabirds may fly through the area each year. The great majority (40-100%) of the flyway population of great skua and little gull use the Strait of Dover to leave the North Sea, as well as 30-70% of the population of terns and lesser black-backed gulls. In addition 10-20% of the red-throated divers and great crested grebes may pass through this bottleneck. Except for great skua, all other species are mainly found in inshore areas (i.e. within 20 km of the shoreline), where the first generation of wind farms will be located. At present, very little is known about the impact of offshore wind turbines on seabirds. Being k-selected species, seabirds are extremely vulnerable to human impacts that affect adult survival. Because of this, and because of a major lack of information on nocturnal migration of seabirds and their reaction towards offshore structures like clusters of wind turbines, great care must be taken. New developments that might have a detrimental impact on resident as well as migrating seabirds must be carefully investigated, especially in this bottleneck area.

During the twentieth century, many coastal areas in Europe changed dramatically due to coastal protection works, human expansion drift and booming beach tourism. As a result the natural area of suitable nesting habitat of many coastal birds has decreased enormously and a large number of species are now listed as threatened. Some species were able to exploit new opportunities offered by human activities, but most coastal birds are now confined to islands, protected areas or artificial sites (nature development projects, restored coastal habitats and even floating rafts). Protection of local resources, as well as further development and management of breeding sites is considered vital in maintaining the populations of threatened coastal breeders. The rationale behind nature restoration and development is often solely based on offering suitable habitat to the birds, while its success is mainly judged from the evolution in the number of birds present. As more and more information becomes available on the reproductive performance of coastal birds, it becomes clear that in some protected areas long-term reproductive success is below self-sustaining levels. Apparently humans are able to create artificial nesting habitats that are highly attractive from the birds’ perspective but are in fact pitfalls for the population in the long term. In contrast, the port of Zeebrugge, Belgium, is an excellent example of an artificial nesting habitat of high quality in terms of attraction as well as reproduction. Here, vast sandy areas were raised in a former marine habitat in the 1980s. The works mimicked natural dynamic processes and coastal breeding birds instantly reacted. Within 20 years, the area has developed from open sea to a breeding site of major international importance. Peak population figures by far exceed the 1% of the total biogeographical population. At present, Zeebrugge harbours more than 4% of the total north-west European Common Tern population, thus making it the largest colony in Europe. It is a highly productive population and acts as a major source of recruits for the biogeographical population as a whole. Until recently, the success of the bird populations was based on the ongoing creation of suitable nesting habitats and management measures, like removal of the vegetation and covering areas with shell fragments. Further development of the harbour, the arrival of the fox and competition for nesting habitat with large gulls are major threats for the bird population. Therefore part of the colony was allocated to a peninsula and further steps are now being considered to preserve this valuable population. Apparently feeding conditions are very good and the harbour itself and its direct surroundings function as a major source of small prey fish of which the availability is facilitated by the heavy shipping traffic and the sheltered conditions of the feeding areas.

Intensification of agriculture since the 1950s has enhanced the availability, competitive ability, crude protein content, digestibility and extended growing seasons of forage grasses. Spilled cereal grain also provides a rich food source in autumn and in winter. Long-distance migratory herbivorous geese have rapidly exploited these feeding opportunities and most species have shown expansions in range and population size in the last 50 years. Results of long-term studies are presented from two Arctic-breeding populations, the Svalbard pink-footed goose and the Greenland white-fronted goose (GWFG). GWFGs have shown major habitat shifts since the 1950s from winter use of plant storage organs in natural wetlands to feeding on intensively managed farmland. Declines in local density on, and abandonment of, unmodified traditional wintering habitat and increased reproductive success among those birds wintering on farmland suggest that density-dependent processes were not the cause of the shift in this winter-site-faithful population. Based on enhanced nutrient and energy intake rates, we argue that observed shifts in both species from traditionally used natural habitats to intensively managed farmland on spring staging and wintering areas have not necessarily been the result of habitat destruction. Increased food intake rates and potential demographic benefits resulting from shifts to highly profitable foraging opportunities on increasingly intensively managed farmland, more likely explain increases in goose numbers in these populations. The geographically exploratory behaviour of subdominant individuals enables the discovery and exploitation of new winter feeding opportunities and hence range expansion. Recent destruction of traditional habitats and declines in farming at northern latitudes present fresh challenges to the well being of both populations. More urgently, Canada geese colonizing breeding and moulting habitats of white-fronted geese in Greenland are further affecting their reproductive output.

The Belgian Continental Shelf (BCS) is characterized by numerous subtidal sandbanks. Their close position to the coastline and the shallowness of the area make them unique, both from an ecological and geological point of view. It has recently been shown that the sandbank system in the Belgian coastal area acts as an intemationally important resting and foraging area for various seabird species. The project 'Structural and functional biodiversity of North Sea ecosystems: species and their habitats as indicators for a sustainable development of the Belgian continental shelf aims to assess the factors that determine and influence the marine biodiversity of the Belgian Continental Shelf. Within this project, an emphasis is made to incorporate all existing and new biodiversity information (community, population and genetic level) on all benthic compartments, including demersal fish, their parasites and birds. Most emphasis is given on the description of the structural aspects of benthic biodiversity in order to find a pattern within the relationship between the biological and the geochemical characteristics of the sediment. The question whether the structuring of ecosystem and species diversity and its functioning is reflected in the genetic structuring of marine taxa on the Belgian Continental Shelf is addressed for the first time.

AMS classifications: 05E30; 51E20; 94B05

Trends in oil pollution in the southernmost (Belgian) part of the North Sea were analysed using a dataset of 37 years (1962-99) of annual national beached bird surveys conducted in February each year. The most abundant seabird groups represented in the beached birds were auks (31 %), gulls (28%), scoters (17%) and Kittiwake (9%). Oil rates of most bird species/taxa indicate a decline in oil pollution, though only Larus-gulls, Common Guillemot and Razorbill show significant reductions. The slope in the linear decreasing trend is steeper in inshore and midshore species, than in pelagic species. A power analysis of the results demonstrated that statistically significant trends in annual indices would be expected within 17 years for Razorbill, 29 years for Larus-gulls and 31 years for Common Guillemot. For other species/taxa, at least 50 years of surveying would be required. Long-term oil pollution monitoring in Belgium should be continued with a major focus on a set of abundant bird taxa, sensitive to oil-pollution and occurring in various marine habitats. Most appropriate for this purpose are grebes (inshore), Larus-gulls, Common Guillemot and Razorbill (midshore) and Kittiwake and Fulmar (offshore).

Several European field studies have shown that wind turbines can have a negative impact on bird populations. Birds can collide with the turbines during local and seasonal migration, or they can become disturbed in their breeding, resting or feeding area’s. In Flanders (Belgium) there are plans to build a large number of wind turbines, in order to produce 3 % renewable energy from the total electricity production in 2004 (and 5 % in 2010). For this reason, between May 2000 and December 2001 a project was performed to study the impact on birds and to produce an atlas of important bird areas and migration routes in order to build up the necessary policy knowledge. The results of this preliminary study are presented in this report. In the period between May 2000 and December 2001 three wind turbine locations were studied: (1) 23 small to medium sized turbines (200-600 kW) at the ‘East dam’ in the port of Zeebrugge, (2) 5 medium sized turbines (600 kW) at the ‘Boudewijn canal’ in Brugge, and (3) 3 large wind turbines (1500 kW) in Schelle along the Schelde river (until March 2002 for collision victims). Weekly searches were done for possible collision victims, and the amount of disturbance was measured for resting, foraging, breeding and migrating birds. In addition, the number of locally migrating birds was measured for a few species, and compared with the estimated number of collisions. We found that the estimated collision numbers varied from 0 to 125 dead birds/wind turbine/year. The mean number of estimated collisions for the 3 different locations varied from 4 to 23 dead birds/wind turbine/year. The mean numbers are comparable with some locations in the Netherlands, but higher than other. Most of the victims were abundant present species as Herring Gull, Lesser Black-backed Gull and Black-headed Gull, but we also found rarer species as Peregrine Falcon, Kestrel, Sparrowhawk, Little Tern, Common Tern, Kittiwake and Stonechat. It is important to know that the mentioned numbers of victims have to be regarded as a strict minimum. More intensive research is necessary to have a better picture of the actual number of small birds that are killed (during seasonal migration daily searches are necessary). On one location it was possible to perform a confined investigation before the turbines were build. It was found that for certain species the number of locally migrating birds was less after the installation of the turbines. The reactions of flying birds varied between species. In many cases large species also showed the largest amount of reactions during flight. This conclusion was also found in a number of other studies in different countries. Because of the short time period and the lack of data of the period before the turbines were build, it was difficult to measure the actual disturbance on resting, foraging and breeding birds. The minimum distances to the turbines were approximately the same as for other foreign studies. Most resting or foraging waterfowl species held a distance of 150-300 m. Studies in other countries have shown that some birds like geese and waders can have a significant disturbance at larger distances of up to 800 m. Our preliminary data suggest that important bird-areas and migration-routes have to be avoided to build wind turbines. The impact is variable between species and locations. In many cases, local studies are needed to estimate the potential impact on birds.

In 1992, the Institute of Nature Conservation (INC) started ship-based surveys on the Belgian Continental Shelf (BCS) to study the spatial and temporal distribution of seabirds. Among other things, the study showed that the Belgian marine waters hold internationally important numbers (> 1% of the biogeographical populations) of several coastal and marine bird species. Also the area proved to be of major importance for several species of migratory birds. Out of the 121 bird species encountered at sea during the period 1992-98, 23 were selected as being true marine species that occur in relatively high densities within the Belgian waters. Of these 23 species six were so-called ‘focal species’, being seabirds which are included in the highest priority lists of international conservation instruments (EC-Birds Directive, Bern Convention or Bonn Convention) and which attain at least 1% of the flyway population in Belgian marine waters in a particular season. Based on the distribution patterns, conservation value, and sensitivity for disturbance or oil pollution of the six focal seabirds several areas of high ornithological importance as well as areas sensitive for disturbance or pollution could be distinguished at the BCS. The avian hotspots at the Westkustbanken and Vlaamse Banken turned out to be the most sensitive areas for disturbance and oil pollution throughout the year, while the sensitivity of other areas varies with the seasons.

This paper summarizes the results of several experiments with bird corpses in the southernmost part of the North Sea and tries to fit this information in the current knowledge of how mortality at sea relates to densities of beached birds on the shoreline. During thirteen drift experiments off the Belgian coast between February 1996 and March 1999, a total of 634 sea- and coastal tagged bird corpses were dropped at sea. Bird corpses were found to drift by the wind at 2.2-3.1% of its own velocity, a value in line with earlier published reports of 2.2-4%. Recovery rates averaged 12%, which is smaller than an overall mean of 22% for thirty published drift experiments worldwide but conform an older ‘standard’ to multiply the number of birds found dead on the beach with ten to arrive at an estimate of total mortality. Despite many complicating factors and a large variability (recovery rates ranging from 0 to 75%) some general patterns appear, useful for the interpretation of beached bird numbers in the Southern North Sea. Recovery rates depend primarily on the dropping location (distance to the coast) and on the size of the bird. An evaluation of bird strandings during 1992-99 at the Belgian coast demonstrates a significant correlation with the cumulative onshore wind speeds of the ten days prior to the survey. Offshore species are much more dependent on enough onshore winds to strand and are found more evenly distributed on the shoreline. Temporal patterns of beached birds usually follow those of seabirds at sea with a time-lag of at least one month. Persistence experiments during three winters with 562 tagged corpses confirm the picture of short residence times in the Southern North Sea. A mean persistence time of merely 5.8-13.3 days and the fact that 50-80% of all birds cannot be recovered anymore after 9 days, indicate how strongly persistence must affect the results of beached bird surveys and drift experiments. Small-sized corpses have persistence times of only 0.7 days, medium-sized birds 5.5 days and large birds persist on average 13 days. Heavily oiled birds are more persistent than other corpses. This and other complicating factors are further discussed in the context of the interpretation of beached bird numbers. We conclude that: (1) beached numbers can be useful and indicate interesting patterns if interpreted with care and in an international context; (2) there is a need for more drift-, persistence- and floating experiments in order to fully understand what a bird corpse does from the moment it dies until it is being found on the beach; (3) special attention should go to differences in ‘behaviour’ of oiled versus unoiled corpses and to what happens with corpses once they have sunk; (4) models should be developed to help predicting patterns of seabird strandings, not to replace drift experiments at incidents or mass strandings.

AMS classifications: 05E30; 51E20; 94B05

The various groups of linear sand ridges off the continental coast of the southernmost part of the North Sea (the ‘Flemish Banks’) have an important seabird conservation value. During an intensive seabird surveying programme from 1992 till 1998 in the Belgian part of it, eleven species were counted in numbers amounting to 1-5% of the flyway population in an area of merely 3500 km². Six of them (Red-throated Diver, Common Scoter, Little Gull, Sandwich Tern, Common Tern, Little Tern) are considered as of international conservation value and were selected as focal species. Hotspots are situated on the shallow Westkustbanken, in the neighbourhood of the Zeebrugge outer harbour and on the Vlaamse Banken. In addition, during the 1990s the Zeebrugge harbour accommodated a medium-sized colony of Sandwich Tern (1650 pairs) and some of the largest colonies of Common (2260 pairs) and Little Tern (430 pairs) of NW-Europe. The present conservation status of these areas is insufficient and marine protected areas (in the widest sense) are needed to safeguard the strongholds for Belgian seabirds. Oil-sensitivity maps indicate that the most vulnerable sites are too close to some of the busiest shipping routes of the world to consider any rerouting measure. Weighing the disturbance-sensitivity of different subareas shows that only on the hotspots for divers and scoters there is a need to restrict boating activity during winter. In addition this southernmost part of the North Sea is a very important corridor for seabird migration. An estimated 1-1.3 million seabirds, with one-third being focal species for conservation, may fly through this bottleneck each year. New developments such as wind parks that might have a detrimental impact on resident as well as migrating seabirds must be carefully investigated.

Intensive seabird surveying during seven years (1992-98) in the Belgian part of the southern North Sea revealed the existence of a land-sea and a longitudinal gradient from the Schelde estuary in the east to the deeper, less turbid waters in the west. Piscivorous species preferring clear water and mid- to offshore conditions (auks, Kittiwake and Northern Gannet) are more abundant in the west. Divers, grebes and Larus-gulls are commoner in the more turbid waters near the mouth of the Schelde estuary. Depth and topography are less dominant as explanatory variables for the distribution of most of the 17 dominant species/taxa. Multivariate and correlative analysis of the abundance of these species could not reveal strong temporal or spatial coherence of seabirds in communities. Highest correlations were found among Larus-gulls scavenging at trawlers, and in the group of auks, Kittiwake and Little Gull. The auks (Razorbill, Common Guillemot) and both gull species were often seen in short-lived multi-species feeding associations over presumed fish shoals. Razorbill is the species that associated most frequently (in 28% of all observations) and it appeared to be a more ‘attractive’ target for Kittiwake (34%) and Little Gull (23%) than the Common Guillemot. Kleptoparasitic behaviour was rarely observed (2.9-6.3% of the observations in skuas). The impact of fishery activities on the distribution of scavenging seabirds (8 of the 17 dominant species) is large. Some 65-70% of all large gulls in the study area were observed in association with trawlers. The general patterns of distribution described in this paper provide the basis for new future research. Major emphasis should go to the interactions between hydrography, prey-availability (pelagic fish) and the specific geomorphologic characteristics of this study-area. Priority species for more detailed research are proposed.

The zonation of non-breeding waterbirds along the Schelde estuary (The Netherlands-Belgium), one of the longest estuaries in NW-Europe with still a complete salinity gradient, including a large freshwater tidal area, was described. Numbers of birds were counted monthly over the period October 1991 to June 1997. Highest numbers of waterbirds were observed in late autumn and winter, with annual peak numbers ranging between 150,000 and 235,000 individuals for the whole estuary. Based on a multivariate analysis different waterbird communities were observed along the salinity gradient. The polyhaline areas of the estuary were numerically dominated by the waders Oystercatcher and Dunlin. Due to the presence of a large brackish marsh in the mesohaline zone, the waterbird community in this area was dominated by the herbivores Wigeon and Greylag Goose. In the oligohaline and freshwater tidal areas, the waterbird community was dominated by duck species, with Teal and Mallard being the most important. The international importance of the Schelde estuary for waterbirds was evidenced by the fact that for 21 waterbird species the 1% level criterion, according to the Ramsar convention, was exceeded. The relation of the observed diversity and community patterns with the functional and habitat diversity of the Schelde estuary as well as the effect of recent conservation measures to preserve this habitat were discussed.