GRAVELAND J (1996) The decline of an aquatic songbird: the Great Reed Warbler Acrocephalus arundinaceus in The Netherlands. LIMOSA 69 (3): 85-96.

Great Reed Warbler Acrocephalus arundinaceus The Dutch Great Reed Warbler breeding population has declined from over 10 000 pairs in the 1950's to 300 pairs at present. There is evidence that this decline is mainly due to deteriorating conditions in the breeding areas and not to drought in Africa, as in the case of the Sedge Warbler A. schoenobaenus. The possibility that changes in reed quality and food abundance contributed to the decline of the Dutch Great Reed Warbler population was investigated in two localities: De Weerribben and Zwarte Meer. Reed characteristics were measured near nests of Great Reed Warbler and Reed Warbler and at randomly chosen sites in reed beds. Reed Warblers are suitable for comparison since the two species overlap in habitat requirements. Moreover, Reed Warblers are quite abundant and have increased. Food abundance in reed beds was determined with emergence traps. Diet was studied by observation of parents feeding nestlings. Great Reed Warblers preferred reeds with slightly thicker, longer stems and a lower density than Reed Warblers. However, the species mainly differed in their preference for reed standing in water (water reed). All Great Reed Warbler nests were located in water reed, where no more than 25% of Reed Warbler nests were located. Within the water reed zone Great Reed Warblers nested much farther from the shore than Reed Warblers. Great Reed Warbler diet in De Weerribben mainly consisted of aquatic larvae of dragonflies, collected in the water reed zone, adult damselflies and dragonflies and moths. Dragonflies and damselflies were rare in Zwarte Meer where Great Reed Warblers main fed on caterpillars of the Peacock Butterfly, obtained behind the water reed zone. Water reed represents the first stage in the succession of the reed marsh. There is evidence that the availability of water reed has markedly declined in The Netherlands and elsewhere in western Europe by terrestrialization, eutrophication and changes in the water table. Dragonflies have declined due to eutrophication as well. Results of this study suggest that deterioration of reed quality and declining abundance of suitable large prey have contributed to the decline of the Great Reed Warbler in The Netherlands.

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