SPAANS B (1994) The breeding birds of the Volkerak-Zoommeer during the first five years after embankment. LIMOSA 67 (1): 15-26.

In spring 1987,2470 ha of tidal flats and salt marshes in the Volkerak-Zoommeer area were embanked by closing the Philipsdam (fig. I). The area became a nature reserve. Water in the area desalinated quickly. Colonization by plants and breeding birds was studied in seven study plots (fig. I) during the first five years after embankment (198892). Rare and colonial breeding species were inventoried in the entire embanked area. In this paper, breeding bird population changes are discussed in relation to vegetation succession. The well-drained former salt marshes differed from the waterlogged former tidal flats with respect to vegetational succession. Former salt marshes were desalinated two years after embankment and after five years the vegetation featured Cirsium arvense, Calamagrostis epigejos, Epilobium hirsutum and Salix spp. Higher parts of former tidal flats also desalinated quickly and featured Aster tripolium, Poa spp, Phragmites australis, Cirsium arvense, Calamagrostis epigejos and Salix spp. However, the lower parts of former tidal flats were still dominated by halophytic plant species five years after embankment. The number of breeding bird species in the study plots increased from 18 in 1988 to 49 in 1992 (fig. 9). The occurrence of Spergularia salina in the study plots showed a similar trend as the number of breeding pairs of pioneer species such as Avocet, Kentish Plover, Little Ringed Plover and Ringed Plover (fig. 2, 3), i.e., a maximum in the third year after embankment. Breeding populations of most pioneer species in the entire embanked area are still increasing (fig. 2,3, app. I). The main reason for this discrepancy seems to be the construction of new islands in the third and fourth years. These islands were initially bare or scarcely vegetated, offering pioneers suitable breeding habitat. These new islands are also attractive for breeding gulls and terns, species which increased during the whole study period (app. I). Breeding densities of meadowbirds, Oystercatcher, Lapwing and Redshank decreased on former salt marshes but increased on the flats (fig. 4); songbirds of the open field tolerated, however, a higher vegetation as long as there were open spots (fig. 5). A number of songbird species appeared on the salt marshes from the first and second year onwards. In early spring, remnants of Cirsium arvense and Epilobium hirsutum of the previous year offered these species sufficient vertical vegetation structure (fig. 6). The second group of songbirds appeared from the fourth year onwards when Salix spp. trees were getting more dominant (fig. 7). At the same time Phragmites australis started to dominate parts of the flats and as a result Reed Warbler breeding density increased, Reed Bunting proved to be less dependent on reed (fig. 8). Management by grazing in order to retard or stop vegetation succession is carried out now in part of the embanked area and will improve habitat for waterfowl and meadowbirds. On the other hand it is recommended to allow undisturbed succession of the vegetation and its breeding bird population in other parts of the area ##### Western Marsh Harrier Circus aeruginosus Black-winged Stilt Himantopus himantopus Pied Avocet Recurvirostra avosetta Little Ringed Plover Charadrius dubius Common Ringed Plover Charadrius hiaticula Kentish Plover Charadrius alexandrinus Mediterranean Gull Ichthyaetus melanocephalus = Larus melanocephalus Little Gull Hydrocoloeus minutus = Larus minutus Black-headed Gull Chroicocephalus ridibundus = Larus ridibundus Common Gull Larus canus canus Lesser Black-backed Gull Larus fuscus European Herring Gull Larus argentatus Common Tern Sterna hirundo Arctic Tern Sterna paradisaea = Sterna macrura Little Tern Sternula albifrons = Sterna albifrons Short-eared Owl Asio flammeus Sand Martin Riparia riparia Common Shelduck Tadorna tadorna Gadwall Anas strepera Mute Swan Cygnus olor Common Teal Anas crecca Mallard Anas platyrhynchos Garganey Anas querquedula Northern Shoveler Anas clypeata = Spatula clypeata Tufted Duck Aythya fuligula Common Kestrel Falco tinnunculus Grey Partridge Perdix perdix Common Pheasant Phasianus colchicus Eurasian Coot Fulica atra Eurasian Oystercatcher Haematopus ostralegus Northern Lapwing Vanellus vanellus Black-tailed Godwit Limosa limosa Common Redshank Tringa totanus Black-headed Gull Chroicocephalus ridibundus = Larus ridibundus Common Gull Larus canus canus Lesser Black-backed Gull Larus fuscus European Herring Gull Larus argentatus Common Tern Sterna hirundo Little Tern Sternula albifrons = Sterna albifrons Stock Dove Columba oenas Common Wood Pigeon Columba palumbus Common Cuckoo Cuculus canorus Short-eared Owl Asio flammeus Eurasian Skylark Alauda arvensis Meadow Pipit Anthus pratensis Blue-headed Wagtail Motacilla flava White Wagtail Motacilla alba Winter Wren Troglodytes troglodytes Dunnock Prunella modularis Bluethroat Luscinia svecica = Cyalnosylvia svecica British Stonechat Saxicola rubicola = Saxicola torquata Common Blackbird Turdus merula Common Grasshopper Warbler Locustella naevia Sedge Warbler Acrocephalus schoenobaenus Marsh Warbler Acrocephalus palustris European Reed Warbler Acrocephalus scirpaceus Icterine Warbler Hippolais icterina Common Whitethroat Sylvia communis Garden Warbler Sylvia borin Willow Warbler Phylloscopus trochilus Common Starling Sturnus vulgaris European Greenfinch Carduelis chloris European Goldfinch Carduelis carduelis Common Linnet Carduelis cannabina Common Reed Bunting Emberiza schoeniclus

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