The Great Reed Warbler (Acrocephalus arundinaceus) is a Eurasian passerine in the genus Acrocephalus. It used to be placed in the "Old World Warbler" assemblage, but is now recognized as part of the marsh and tree-warbler family (Acrocephalidae). A. arundinaceusare medium-sized birds and are the largest of the European warblers. They breed throughout mainland Europe and Asia and migrate tosub-Saharan Africa in the winter. Great reed warblers favor reed beds as their habitat during breeding months, while living in reed beds, bush thickets, rice fields, and forest clearings during the winter. Great reed warblers exhibit relatively low sexual dimorphism, and both genders of the species are similar in appearance. This species mates both polygynously and monogamously.