GRAVELAND J (1997) Density and nest success of Reed Warbler Acrocephalus scirpaceus and Sedge Warbler Acrocephalus schoenobaenus. LIMOSA 70 (4): 151-162.

In discussions between conservationists, managers and reed growers on the optimal management of reed beds for the benefit of marsh birds, cutting of reed is a controversial issue.
      This paper presents results of a study on nest density and breeding success of Reed Warblers Acrocephalus scirpaceus Sedge Warblers A. schoenobaenus in cut and uncut reed, carried out in the Dutch National Park De Weerribben in 1993-95. Results are based on data from 215 Reed Warbler nests and 85 Sedge Warbler nests: Both species showed a marked preference for nesting in uncut vegetation (Reed Warbler nests in reed. Sedge Warblers nests in reed and sedges). Nest density in uncut vegetation was 1.5-10 (Reed Warbler) and 6-25 times Sedge Warbler) higher than in cut vegetation. Nest densities m cut vegetation in comparison with uncut vegetation differed markedly between years. These differences were related to the number of birds present, the availability of uncut reed and spring temperature. Because of the rapid growth of young shoots, cut reed provided an alternative for uncut reed sooner in a warm spring than in a cold spring.
      Reed Warblers started nesting 6-12 days earlier in uncut reed than in cut reed, the difference depending on sprig temperature. In Sedge Warblers, there was no clear difference in laying date between cut and uncut vegetation. Clutch size and fledging success in broods of Reed Warbler and Sedge Warbler that were not predated did not differ between cut and uncut vegetation. However, the nest predation rate was 1.7 (Sedge Warbler) and 2.2 (Reed Warbler) times higher in cut vegetation than in uncut vegetation. The predation rate of Sedge Warbler nests was 1.7 (cut vegetation) to 2.3 times (uncut) higher than m Reed Warbler nests. Ground predators, in particular mammals, were the main predators of Sedge Warbler nests. The Cuckoo appeared to be the main predator of Reed Warbler nests. About 6% of Reed Warbler nests were parasitized by Cuckoos, compared with none for Sedge Warbler nests.
      In conclusion, the presence of uncut vegetation, in particular uncut reed, is important for Reed and Sedge Warblers. It allows them to nest earlier, thus providing them with more time for replacement or second broods and it reduces the risk of predation in comparison with cut vegetation. However, leaving reed uncut accelerates the process of natural succession to carr woodland and will thus negatively affect the density of reed-dwelling birds m the long term. To determine the optimal reed cutting strategy for reed-dwelling birds, it is essential that data on densities and nesting success of birds in cut and uncut reed are integrated with data on the relationship between the frequency of reed-cutting and the rate of succession of reed marshes.

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