Patterns of morphological and molecular variation in Acrocephalus newtoni on Madagascar

The endemic Modagascar Swamp-Warbler, Acrocephalus newtoni, generally occurs in lowland or upper mid-elevation (to c. 1800 m) aquatic habitats associated with stow-moving river, stagnant marshes and swamps in most regions of the island. In 1995, a population of swamp-warbler was found above tree-line in a dry ericoid zone of vegetation on the Andringitra Mossif (at 2050 m) in south-central Madagascar, a very different habitat from that typically occupied by A. newtoni. Given the typical habitat specificity of members of the genus Acrocephalus, we expected the Andringitra birds to show differences at the specific level in comparison to marsh-dwelling A. newtoni. Using morphological and molecular characters it was found that the Andringitra population cannot be differentiated from typical A. newtoni.