Reed die-back, water level management and the decline of the great reed warbler Acrocephalus arundinaceus in The Netherlands

Several species of migratory marsh birds have declined in Central and Western Europe. An important question is whether this decline is primarily caused by loss of wetlands on the wintering grounds in Africa or by a decline in habitat quality in the breeding areas. Significant losses of Reed Phragmites australis beds have been reported in many European countries, presumably as a result of unnatural water level regimes and eutrophication. We studied the reed requirements of nesting Great Reed Warblers Acrocephalus arundinaceus in relation to reed availability in The Netherlands. Numbers of Great Reed Warblers have declined dramatically but the species is less dependent on marshland in its winter quarters than most other migratory marsh birds. Great Reed Warblers nested almost exclusively in reed standing in water and this type of reed has become scarce in The Netherlands. The present distribution of water reed indicates that the man-induced reduction in natural fluctuations of the water level has been an important factor in its decline. Water reed represents the first stage of the succession in a reed marsh. Eventually, loss of water reed will therefore affect the entire marsh bird community. Restoration of natural water level fluctuations seems the most effective course for remedial action, but will be difficult to accomplish because of the conflicting interests of nature and agriculture