Birds of reed vegetation: shrubs and trees are encroaching marshland
Birds of reed vegetation have declined, largely because the reed vegetation fringing marshland has declined.
Trends
On average, birds of reed vegetation are now less common in marshes and swamps than they were around 1950. In the last 10 years the number of breeding pairs has remained more or less stable, although some species, particularly the great reed warbler, are still declining.
The birds of reed vegetation have declined because reed vegetation is dwindling. The reed fringes of open water are becoming narrower, because the water quality is poor and the water level no longer fluctuates naturally (high in the winter and low in the summer). Furthermore, reed is being ousted by shrubs and trees, a process reinforced by the repercussions of water draw-down and by the eutrophication of the surface water. And the annual cutting of the reeds is bad for birds of reed vegetation.
The bittern, great reed warbler, sedge warbler, savi's warbler and little bittern are on the Red List of birds. A species protection plan has been drawn up for marsh birds.
Technical note
The Species Group Trend Index (SGTI) is the mean index for the following species of reed vegetation (the benchmark year is 1950 (=100) and the trend since 1990 is given in parenthesis): marsh harrier (more or less stable), great reed warbler (decrease), reed warbler (stable), sedge warbler (increase), bittern (increase), Savi's warbler (no clear trend) and little bittern (more or less stable).
The figure shows the SGTI. The index figures for the great sedge warbler are given separately.
The figures refer to the bogs in carr peat areas and the swamps in the marine clay area and the river region. The data are from the Ecological Monitoring Network's national network for monitoring breeding birds.
References
- Boer, T. den (2000). Beschermingsplan moerasvogels 2000-2004. Rapport nr.47. Directie Natuurbeheer. Ministerie van Landbouw, Natuurbeheer en Visserij. Wageningen.
- Dijk, A.J. van, L. Dijksen, F. Hustings, D. Zoetebier en C. Plate (2001). Broedvogelmonitoring Project. Jaarverslag 1998-99. SOVON-rapport 2001/03. Beek-Ubbergen.
- Dijk, A.J. van, M.J.T. van der Weide, R. Kleefstra, D. Zoetebier en C. Plate (2001). Kolonievogels en zeldzame broedvogels in Nederland in 1999. SOVON-monitoringrapport 2001/08. Beek-Ubbergen.
- Graveland, J. (1999). Waterriet, moerasvogels en peildynamiek. De Levende Natuur, 100 (2): 50-53.
