Taxonomy and Systematics
Otto Finsch was the first naturalist to visit the island of Nauru, stopping for six hours on 24 July 1880 while travelling from the Marshall Islands to the Solomon Islands. His 1881 report included a warbler he initially identified as the Carolinian Reed Warbler. By 1883 he considered it to be a new species, Calamoherpe rehsei. The generic name Calamoherpe is now recognised as a synonym of Acrocephalus, leading to the current binomial name. The generic name Acrocephalus derives from the Greek akros, meaning "topmost", and kephale, meaning "head". The akros part of the name may have been given through confusion with acutus, and taken to mean "sharp-pointed", referring to the angular head shape typical of this genus. The synonym Calamoherpe is from the Greek kalamos, meaning "reed", and herpes, meaning "creeping thing". Finsch named the species after Ernst Rehse, a German ornithologist and collector and one of Finsch's travelling companions. Since the original descriptions, little has been written about the species, and details about its ecology and behaviour are poorly known.
Though the Nauru Reed Warbler is generally accepted as a species, some authorities, such as H. E. Wolters in Die Vogelarte der Erde (1980) and Howard and Moore in A Complete Checklist of the Birds of the World (1991), have considered it a subspecies of Acrocephalus luscinius, the Nightingale Reed Warbler. Recent DNA studies have affirmed its status as a separate species. It is considered monotypic, meaning there are no recognised subspecies. The species is known by the English common names Finsch's Reed-warbler, Nauru Warbler, Pleasant Warbler, the Nauru Reed-warbler, and the Nauru Reed Warbler. In the native Nauruan language, it is known as Itsirir.
A 2009 phylogenic study of the family Acrocephalidae did not include this species, and as recently as 2010 its relation with other members of the genus was unknown. A 2011 analysis of mitochondrial DNA showed that the Nauru Reed Warbler forms a clade with the Australian Reed Warbler, the Bokikokiko, the Marquesan Reed Warbler and a now-extinct species from Pagan Island in the Marianas. The closest relative of the Nauru Reed Warbler appears to be the extinct warbler from Pagan. This is currently named as a subspecies of the Nightingale Reed Warbler, A. luscinius yamashinae, but that species is polyphyletic, and the Pagan form, which has been proposed as a new species, the Pagan Reed Warbler, is in a different clade to Nightingale Reed Warblers from other islands.
The pattern of colonisation of the Pacific islands and eventually Australia by the Acrocephalus warblers from Asia was complex, with multiple colonisations of even remote archipelagos. Although the Hawaiian islands were colonised about 2.3 million years ago, the other islands were reached much more recently, in the mid-Pleistocene (between 0.2–1.4 million years ago) or even later. The nearest other warblers geographically to Nauru are the Carolinian Reed Warbler and the Nightingale Reed Warbler.
Read more about this topic: Nauru Reed-warbler