Unusual Nests in the Great Reed Warbler Acrocephalus arundinaceus: Reuse of Nests in the Same Season and Unusual Forms of Nest Construction

Abstract

Although previous studies have reported on rare nesting behaviour such as nest reuse and/or unusual nest construction in open nesting passerines, very little is known about these rare phenomena. We found and monitored 1224 Great Reed Warbler nests between 2008 and 2017. In three nests, we found reuse of nests in the same season; two nests were reused after a Cuckoo chick had disappeared and one nest was reused after a damaged egg had been ejected. In two other nests, we observed that replacement nests were built directly under the original nest, using the same reed stems. These observations suggest that there may be cases when breeding Great Reed Warblers benefit from performing unusual yet adaptive behaviour, such as conserving energy and time when nests are reused, or recognizing the advantages of original nests, e.g. they may serve as cover and/or concealment.