Effects of Reed Cutting on Density and Breeding Success of Reed Warbler Acrocephalus scirpacaeus and Sedge Warbler A. schoenobaenus

Abstract

The management of reedbeds for birds is often a controversial issue in discussions between conservationists, reed harvesters and managers. At the same time, data on the density and nesting success of birds in cut and uncut reed are scarce. This paper presents the results of a study on the density and nesting success of Reed Warblers Acrocephalus scirpaceus and Sedge Warblers A. schoenobaenus in cut and uncut reed in a peat marsh, De Weerribben National Park in the Netherlands in 1993-1995. Depending on year, densities of Reed Warblers were 1.2-2.5 times higher in uncut reed than in cut reed, while densities of Sedge Warblers in uncut reed and other vegetation were 6-50 times higher than in cut vegetation. Reed Warblers nested 6-12 days earlier in uncut reed than in cut reed. No difference could be detected in laying dates of Sedge Warblers in cut and uncut vegetation, presumably because many Sedge Warblers in cut vegetation nested in small remnants of uncut vegetation. There were no differences in clutch size or fledging success in non-depredated nests of Reed Warblers and Sedge Warblers between cut and uncut vegetation. However, the predation rate of Reed Warbler nests in cut vegetation was 2.2 times as high, and of Sedge Warbler nests 1.6 times as high as in uncut vegetation. Sedge Warblers started to nest two to three weeks earlier and their nests were more often preyed upon than Reed Warblers' nests, in particular by ground predators. This may explain why Sedge Warblers more strongly preferred uncut reed than did Reed Warblers. Contrary to Sedge Warblers, Reed Warblers close to trees were parasitized by Cuckoos Cuculus canorus, which may explain why Reed Warblers nested in lower densities close to trees than farther away from trees. The results show that uncut reed is more suitable for nesting Reed Warblers and Sedge Warblers than cut reed because it allows them to nest earlier - and thus to raise on average more clutches per season - and because the birds suffer a lower predation risk.