Kluijver H.N. (1955) Das Verhalten des Drosselrohrsängers, Acrocephalus arundinaceus (L.), am Brutplatz mit besonderer Berücksichtigung der Nestbautechnik und der Revierbehauptung. ARDEA 43 (1-3): 1-50

The behaviour of the Great Reed Warbler, Acrocephalus arundinaceus; with special reference to nest building and territorial defence. The birds were observed in a pond in the valley of the Rhine near Rhenen, the Netherlands. Since the Great Reed Warbler nests in a very uniform habitat, viz., in dense vegetations of perpendicular reed stems, its nest building behaviour is both specialised and easy to describe and analyse. The birds arrive at their breeding stations between the end of April and the end of May; males arrive before the females. Adverse weather conditions can delay arrival (Fig. 1). In May and June males are distinguishable from females by the worn state of their plumage. The sexes differ in behaviour as well, the males defending their territories and singing persistently and loudly, the females singing much less frequently and never as loudly. The female alone builds the nest and incubates. In other Reed Warblers, e.g., the Common Reed Warbler, Acrocephalus scirpaceus, both sexes incubate. In Central Europe the male of the Great Reed Warbler takes a share in incubation. Some males do not settle in reed beds but in Typha or Scirpus. Such males fail to breed, since no female can build in these plants. Some females try, but they have to give up because the heavy nest, which is built of wet material, receives insufficient support. Courtship, and particularly the selection of a nest site, is described. In nest site selection the male seems to play the more important role; he calls the female to the site of his choice by a peculiar soft .whistle. The female dips the nest material in water before working it into the nest. This renders the material flexible and makes it stick to the reeds. The number of instinctive activities used by the female in building is limited. The bill is used in carrying the material and in weaving it round the reed stems. The nest cup is moulded by a characteristic trampling movement of the legs ('scraping'), a movement found in 'many other species of birds, both Passerines and non-Passerines. Unlike some other Passerines the Great Reed Warbler does not use scraping for raising the rim of the nest; this is done by the bill. The nest cup is very deep, which prevents loss of eggs and young during strong wind. Although the males stake put territories, their distribution in the available reed beds is not uniform since territories tend to be clustered together. This has perhaps to do with the males' quarrelsome nature. Males were often observed even to cross a considerable stretch of open water to start an argument with a male on the other side. Polygamy was observed several times. Where few and small reed beds were available among Typha or Scirpus one male might have two or three mates, each with a nest and brood. Such nests were sometimes no more than 10 metres apart. Reports in the literature of Great Reed Warblers nesting in colonies may have to be accounted for in this way. In some broods the incubation period (14 days) and the fledging period (12 days) were established. At the moment of leaving the nest the fledglings cannot fly, but they hop skilfully from one reed stem upon the other. A disturbance at the nest may cause them to do this already when eight days old.