WINDEN J VAN DER & MOREL T (2002) Breeding birds of the peat marshland area in the provinces Noord-Holland and Utrecht in 1967-94. LIMOSA 75 (2): 57-72.

On the border of the provinces Noord-Holland and Utrecht one of the larger Dutch peat bog marshland systems is situated: The Vechtplassen (Fig. 1). Parts of the area are assigned as Special Protection Area under the EU Bird Directive. The area is considered as important for marshland birds and species of open waters. Open water, marshlands and wet alder forests dominate the area. The area has changed considerably as a result of human activities. In the Middle Ages bogs have been exploited and large open waters were created. In the last century, the water management changed completely as a result of changes in land use and drainage. This resulted in a shortage of natural oligotrophic waters in summer. To compensate for this loss, increasing amounts of alkaline Rhine water were diverted into the ecosystem. This resulted in a strong eutrophication with a significant effect on vegetation. Pioneer vegetations typical for the historic situation like Water Soldier, sedges and reedbeds disappeared almost completely and in their place nymphaeids and alders colonised the area (Fig. 2).
      Information on the effects of these changes in habitats on birds has not been documented systematically till now. In three periods breeding bird census work was executed: 1967- 70, 1978-85 and 1989-94. In these periods scarce and characteristic bird species for marshlands, open waters and forests were investigated completely (Table 1). From this list, 20 species declined of which 17 species declined by more than 50%. On the other hand 17 species increased of which 14 by more than 50%. Since the sixties, 15 species colonised the area. Most striking was the decline of typical marshland species like Great Bittern, Little Bittern, Black Tern and Great Reed Warbler, and the strong increase of forest species like Eurasian Woodcock and Eurasian Goshawk (Table 1). The decrease of marshland species and the increase of forest birds were most clear in the sixties and seventies. For many species the decline in the Vechtplassen was stronger than in The Netherlands as a whole, indicating that local factors were important. This holds especially for species from pioneer marshland vegetations like inundated reedbeds. Forest species increased more strongly, and species of open water landscapes did not differ in their trend from the overall Dutch trends (Fig. 3). For six species typical for specific marshland habitats the trend is described in more detail, supporting the general findings (Fig. 4).
      The changes in water quality and vegetation have resulted in a significant change in bird communities and numbers in the Vechtplassen. Typical marshland species declined while species of forests and dryer habitats increased. Red List species especially suffer from the negative effects. The nature policy in the area is to put effort in the protection of typical marshland species in the first place. To be effective, measurements on a large scale seem to be necessary. In the near future nature restoration projects have been planned as well as changes in water management. So far these plans are still rather local and of small proportions. It is recommended to enlarge these activities and to monitor the effects on bird populations in the future.

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