The complex systematics of the <i>Acrocephalus</i> of the Mariana Islands, western Pacific

Abstract

The Nightingale Reed-Warbler (Acrocephalus luscinius) is known from six islands of the Mariana Archipelago in the Pacific Ocean. A recent phylogeny of the reed-warblers of the Pacific islands suggested however that the species was polyphyletic, the result of at least three independent colonisations. We present here a complete phylogeny of the Mariana reed-warblers that includes two populations, from Alamagan and Aguiguan, not yet studied using molecular techniques. Both of these populations belong to the Pacific Acrocephalus radiation, with birds from Alamagan closely related to the Saipan population, and those from Aguiguan having unresolved relationships within the Micronesian clade. These results suggest that the Mariana Islands experienced multiple colonisations by reed-warblers. We use a combination of molecular phylogeny and biometry of museum specimens to propose a new species-level taxonomy for Acrocephalus of the Marianas. These results have conservation implications for the two remaining populations, on Alamagan and Saipan, which probably belong to the same taxon, Acrocephalus hiwae (Nightingale Reed-Warbler).