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Theo Vulink J.,Rijkswaterstaat Waterdienst | Van Eerden M.R.,Rijkswaterstaat Waterdienst | Drent R.H.,University of Groningen
Ardea | Year: 2010

The man-made wetlands in young polders in The Netherlands are important stopover and wintering sites for geese. We studied trends in vegetation composition and goose density in two study areas. One was located in a nature reserve situated in a polder reclaimed from an estuary, the other in a reserve in a polder reclaimed from a freshwater lake. In the former we compared an area of spontaneous vegetation succession with a summer-grazed area. In the latter the effect of reed Phragmites australis cover and height on field selection of geese was studied in an area grazed year-round by cattle and horses. In both study areas the area of short grassland (reed cover about 1%, reed height <0.5 m) was found to be significantly positively related to the grazing density of cattle and horses. Migrating and wintering Greylag Geese Anser anser and Barnacle Geese Branta leucopsis preferred to feed on these extensive short grasslands. In the ungrazed part of the study site in the reclaimed estuarine area, there was an inverse relation between goose density and the ousting of pioneer species of saline habitats and short grasses by tall species such as Calamagrostis epigejos, Phragmites australis, tall herbs and shrubs. Summer grazing by cattle and horses at stocking rates of about 0.4 to 0.9 animals/ha, retarded the vegetation succession to some extent, which resulted in a goose density being higher in the summer-grazed area than in the ungrazed area. The implications for management are that the more desalinated the area becomes and the higher its clay content, the higher the stocking rate must be to retard the vegetation succession.


Van Rijn S.,Rijkswaterstaat Waterdienst | Zijlstra M.,Rijkswaterstaat Waterdienst | Bijlsma R.G.,Doldersummerweg | Bijlsma R.G.,University of Groningen
Ardea | Year: 2010

The coastal wetlands of The Netherlands have always served as winter haunts for juvenile and immature White-tailed Eagles from breeding populations further north and east. Even as these populations were at their lowest ebb by the 1960s and 1970s, each winter a few individuals showed up, invariably favouring large wetlands with a good supply of wintering, mainly herbivorous, waterfowl. An analysis of the presence of eagles in the wetland Oostvaardersplassen showed that wintering numbers as well as the duration of individual stays increased as a function of the number and biomass of waterbirds present. During the pioneering stage of this newly reclaimed area the dynamic vegetation produced huge seed supplies that attracted vast numbers of herbivorous waterbirds. The increase in eagle numbers in the Oostvaardersplassen reserve preceded the recovery of the northern and eastern breeding populations of Whitetailed Eagles, but did not increase any further after reaching a maximum of 3-4 wintering birds, despite the fact that wintering numbers elsewhere in The Netherlands continued to rise in the wake of the increasing breeding population elsewhere in Europe. It is argued that 'core area' Oostvaardersplassen became saturated each winter in the 2000s. Additional eagles reaching The Netherlands spent the winter at alternative sites with smaller food supplies. In 1997-99, new waterbodies were created in the dry border zone of Oostvaardersplassen. The subsequent boost in waterbirds and fish may have triggered - in combination with the presence of undisturbed breeding habitat - the summering, and eventual breeding, of White-tailed Eagles from 2004 onwards. Water management towards improving dynamics in larger wetlands (both estuarine and riverine) jnay further boost food supplies for waterfowl and, hence, create suitable habitat for White-tailed Eagles elsewhere in The Netherlands.


Beemster N.,Rijkswaterstaat Waterdienst | Beemster N.,University of Groningen | Troost E.,University of Groningen | Platteeuw M.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

A study on Bearded Reedling Panurus biarmicus feeding habits in combination with a sample-wise breeding bird survey of the marshland zones of the Dutch wetland Oostvaardersplassen shows clear-cut spatial differences in densities and habitat use. The more mature stands of Reed Phragmites australis constitute the main nesting area, while the more open, younger stands, particularly when inundated and grazed by moulting Greylag Geese, provide the main feeding areas. Arthropod, and especially Chironomid, densities were generally higher in grazed Reed stands and frequent feeding flights were carried out by parent birds between grazed and ungrazed parts of the area during chick raising. Chironomids also proved to constitute the main prey items brought to the nests. Apart from higher prey densities in grazed stands, better detectability as well as better accessibility of the lower vegetation layers are also likely to contribute to the habitat preference of insect-feeding Bearded Reedlings. When in winter the birds shift to Reed seeds, patches with higher seed index hold higher densities of feeding birds. When seed index drops below a certain level, density of birds is low and independent of seed index. The highest seed production is associated with rejuvenated Reed stands, recovering from previous grazing. Bearded Reedlings thus highly depend on the early successional stages of Reed stands. Temporal and spatial habitat diversification is mediated by changing water levels and rejuvenation caused by grazing geese. A number of other marshland bird species depend on this type of vegetation, and wetland management should therefore aim at favouring the natural processes governing Reed succession.


Verbiest H.,Research Institute for Nature and Forest | Breukelaar A.,Rijkswaterstaat Waterdienst | Ovidio M.,University of Liège | Philippart J.-C.,University of Liège | Belpaire C.,Research Institute for Nature and Forest
Ecology of Freshwater Fish | Year: 2012

Downstream migration of female silver eel Anguilla anguilla (L.) was studied by remote telemetry in the lower part of the River Meuse (Belgium and the Netherlands) using a combination of nine detection stations and manual tracking. N=31 eels (L T 64-90cm) were implanted with active transponders and released in 2007 into the River Berwijn, a small Belgian tributary of the River Meuse, 326km from the North Sea. From August 2007 till April 2008, 13 eels (42%) started their downstream migration and were detected at two or more stations. Mean migration speed was 0.62m·s -1 (or 53km·day -1). Only two eels (15%) arrived at the North Sea, the others being held up or killed at hydroelectric power stations, caught by fishermen or by predators or stopped their migration and settled in the river delta. A majority (58%) of the eels classified as potential migrants did not start their migration and settled in the River Berwijn or upper Meuse as verified by additional manual tracking. © 2012 John Wiley & Sons A/S.


Ruessink B.G.,University Utrecht | Ramaekers G.,Rijkswaterstaat Waterdienst | Van Rijn L.C.,University Utrecht | Van Rijn L.C.,Deltares
Coastal Engineering | Year: 2012

Nearshore morphodynamic models are computationally demanding, especially when the time scale of interest is weeks or longer. Hence, they often rely on a simple parameterization or non-linear wave theory to estimate the skewed-asymmetric shape of the near-bed, free-stream wave orbital motion, relevant to the prediction of onshore sand transport during mild wave conditions. Recently, Abreu et al. (2010) presented a simple analytical expression for this shape. Here, we present parameterizations to estimate the non-linearity parameter r and phase φ in this expression, such that the non-linear orbital motion can be estimated efficiently from values of the significant wave height H s, wave period T, and water depth h, standard output of nearshore morphodynamic models. The parameterizations are based on a data set of 30.000+ field observations of the orbital skewness S u and asymmetry A u, collected under non-breaking and breaking wave conditions. Consistent with earlier observations, we find that the Ursell number, which includes H s, T and h, describes the variability in S u and A u well and we use it to link H s, T and h to r and φ. The comparison of our findings to another large field data set suggests that wave non-linearity depends weakly on wave directional spread and that our parameterizations may underestimate S u for narrow-banded swell and (unidirectional) laboratory conditions. Furthermore, the use of the parameterizations is not advised on bed slopes steeper than in our data set (i.e., >1:30). © 2012 Elsevier B.V.


Borcherding J.,University of Cologne | Breukelaar A.W.,Rijkswaterstaat Waterdienst | Winter H.V.,Wageningen University | Konig U.,University of Cologne
Ecology of Freshwater Fish | Year: 2014

Anadromous North Sea houting (NSH, Coregonus oxyrinchus) was historically distributed in the Wadden Sea extending from Jutland (Denmark) to the Schelde delta (Netherlands). The species has been considered extinct in the Rhine since the 1940s; however, a successful re-introduction programme re-established a self-reproducing population. Telemetry data of adult NSH (NEDAP TRAIL System®) were used for a first description of the timing of spawning migrations of NSH in winter, but also suggested that the River IJssel, a lower branch of the Rhine, may serve as spawning ground. This was further proven in spring 2010 with drift net catches of 218 freshly hatched NSH larvae sampled directly upstream from Kampen, where the IJssel discharges into Lake IJsselmeer. These larvae did not differ between controls from a hatchery that were about 12 h of age, indicating that the drifting larvae of NSH must have hatched in upstream areas of the River IJssel. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.


Platteeuw M.,Rijkswaterstaat Waterdienst | Foppen R.P.B.,Wageningen University | Van Eerden M.R.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

All over Europe, wetlands have decreased in size, lost their original dynamics and became fragmented as the consequence of an ever increasing human land use. These processes have resulted in losses of nature values, among which declines in marshland bird populations. Ecological restoration of wetland systems follows from initiatives like EU Bird and Habitat Directives and Water Framework Directive, but may be, in itself, too costly to be widely applied. More promising perspectives to reinforce the wetland part of the ecological network Natura 2000 might come into focus when combined with spatial water management which is primarily aimed at more sustainable safety against flooding. In this way, the wetland network may acquire a wider public and political support. Knowledge on scale-related habitat use of wetland birds can play a role in the process of spatial planning. We illustrate this point by distinguishing four levels of spatial and temporal habitat use by wetland birds, and giving examples for each. The four levels are: (1) birds on stopover sites during migration, (2) territorial breeding birds, (3) colonial breeding birds, and (4) staging birds on wintering sites. This asks for ecological coherence on different scales, e.g. on the international level of migration flyways, on the regional level of landscapes and on the local level of individual wetlands. It is advocated that wetland ecologists dedicate themselves more specifically to quantifying the relevant data on habitat use of birds on each of these scale levels. Meanwhile, spatial planners should try to incorporate them into their efforts in realising combinations of ecological restoration or rehabilitation of wetlands and solutions for sustainable water management. These combinations might turn the tide for some seriously threatened species of marshland and wetland birds.


Voslamber B.,Rijkswaterstaat Waterdienst | Voslamber B.,Dutch Center for Field Ornithology | Platteeuw M.,Rijkswaterstaat Waterdienst | Van Eerden M.R.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

After having almost completely vanished from The Netherlands by the 19th century, from the 1970s onwards the Great Egret is increasing in numbers again, particularly in the newly created wetland of Oostvaardersplassen. During the first 25 years, the rate of re-colonisation has been extremely low, the resident population never exceeding five breeding pairs. From 2000 onwards, however, following the extension of the surface area of shallow marshland, the number of breeding birds increased to 45 pairs. This paper deals with the feeding ecology of the Great Egret during 1976-99, when numbers were at a low level. Individual differences in food choice and feeding habits were studied in order to gain insight into the key factors for establishing and maintaining a healthy population. Observations on foraging birds were carried out during 1987-92. The birds foraged mostly within the reserve. From March to July they preferred foraging in ditches, changing to Reed borders of shallow pools and dry grasslands from August onwards. In the ditches, Three-spined Stickleback Gasterosteus aculeatus, other small fishes and tadpoles were the main prey (91.4% of all prey items). In the shallow water bodies the egrets caught almost exclusively sticklebacks, and in grasslands Common Voles Microtus arvalis. One bird was observed feeding near fishing boats, taking Perch Perca fluviatilis and Roach Rutilus rutilus of 10-20 cm length. When feeding on sticklebacks, a Great Egret had to forage for 1.5 to 3 hours to fulfil its daily needs. When scavenging on larger fish around fishing boats only 15 minutes sufficed, but the energy expenditure was likely to be higher due to commuting flights and interspecific competition with Grey Herons Ardea cinerea. However, for the majority of Great Egrets the shallow and transparent water in ditches and pools with a high abundance of young sticklebacks and some coverage with emergent vegetations proved to be the most profitable feeding habitat. The decisive factor underlying the spectacular increase in recent years has probably been the creation of clear and shallow freshwater pools and inundated grasslands in the formerly dry border zone of Oostvaardersplassen. These foraging grounds lie close to undisturbed breeding sites. This finding may prove useful for wetland restoration elsewhere in The Netherlands.


Van Eerden M.R.,Rijkswaterstaat Waterdienst | Lenselink G.,Rijkswaterstaat Waterdienst | Zijlstra M.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

In The Netherlands, arising in geological time as the delta of the rivers Rhine, Meuse and Scheldt, a considerable change in landscape occurred during the Holocene period due to sea level rise. In more recent times this change was dramatically enforced by human actions. This started with the opening up of the large woods on higher soils, some 4500 years BP. It is estimated that the country was only populated then by a few thousand people. During the next 2000 years, the extensive forest clearing continued, and up to approximately 60% of the upland area changed into grazed woodland. Over-exploitation during the Middle Ages resulted in extended heathlands, which covered up to 40% of the total area of upland sands by 1500 AD. Today woodlands cover only 1 promille of the surface area it covered 7000 years ago. Wetlands remained undisturbed for a long period, but they have become seriously affected since the late Middle Ages; the construction of dikes, embankments and drainage have caused the area of wetlands to shrink dramatically. Especially when in the 19th and 20th centuries, as a result of the introduction of steam and later diesel and electric engines, large-scale projects could be realised. This led to the disappearance of many freshwater lakes and the almost complete loss of the area of brackish water, the natural link between sea water and freshwater. Although the influence of Man upon the Dutch landscape commenced some 4500 years ago, it is only during the last 600 years that wetlands have been affected. Particularly the last 100 years have been crucial with respect to drainage and cultivation. By reconstructing ancient landscapes, an attempt has been made to describe the species composition and numerical abundance of waterbirds, starting 7000 years BP. Two species have become extinct in the territory, many others show changes in abundance. The start of agriculture has caused a major change in the food provisioning of many herbivorous waterbirds. Over the last 7000 years, a sevenfold increase of the number of herbivorous waterfowl is estimated. On the other hand the number of fish-eaters, benthos-eaters and planktivorous waterbirds has declined, their available habitat now having diminished by 45%, 36% and 55% respectively with respect to the Late Subatlantic period, c. 850-1350 AD.


Voslamber B.,Rijkswaterstaat Waterdienst | Vulink J.T.,Rijkswaterstaat Waterdienst
Ardea | Year: 2010

The relationship between reed Phragmites australis cover of ditches and habitat use by marshland birds was studied in an experimental area of the Oostvaardersplassen nature reserve in The Netherlands. Water table and grazing by cattle and horses had an important impact on the development of P. australis in ditches and pools, resulting in three different types of habitat: deep open water, shallow open water and shallow water with P. australis vegetation. Shallow water bodies with a reed cover of less than 10% were most frequently visited by foraging Eurasian Spoonbill Platalea leucorodia, Smew Mergellus albellus, herons, ducks, waders and rails. Breeding grebes and marshland passerines, however, preferred parts with more reed cover. It is concluded that the creation of shallow water bodies, together with adjusted water table management and grazing pressure are suitable tools for restoring habitats preferred by marshland birds.

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