A comparison between various populations of the Great Reed Warbler Acrocephalus arundinaceus was made using published and unpublished data. The comparison showed that most differences are consistent with a division into subspecies. The majority of birds from the nominate subspecies go through a complete moult in late autumn in north Africa, and then continue migration to winter quarters south of the equator. The majority of the eastern subspecies moult completely just after the breeding season. In contrast the orientalis birds spent extremely short periods on migration and long periods in the winter quarters. Orientalis also show more habitat tolerance (breeding in bushes, small trees, and no water), higher breeding density, less nestling starvation, and more Cuckoo Cuculus canorus brood-parasitism.However, some of these features may be due to the fact that some of orientalis populations live in extremely changed (man-made) habitats. On the other hand, clutch-size, total nest-losses, eggs hatchability, fledglings production, and nestling diet composition showed interpopulation variation independent of the subspecies division.