GPS tracking of the two subspecies of the Eastern Buzzard (Buteo japonicus) reveals a migratory divide along the Sea of Japan

In the Far East, multiple avian lineages show a common divergence pattern between the Eurasian continent and the Japanese Archipelago across the Sea of Japan. Buteo japonicus burmanicus and Buteo japonicus japonicus are often regarded as a pair of subspecies of the Eastern Buzzard that differentiated in the Far East during the Pleistocene. However, the background to their differentiation remains unknown because their taxonomic ambiguity prevents researchers from comparing their migration routes, distribution ranges and other characteristics. Here, we investigated differences in the migration routes and distribution ranges of the two genetically identified subspecies. We identified 28 B. j. burmanicus and B. j. japonicus individuals based on their mitochondrial DNA sequences and tracked their migration from Japan using GPS tracking devices. Three key results were found. First, B. j. burmanicus wintered in western Japan. Second, B. j. burmanicus migrated to the Eurasian continent and flew north along the eastern coast of the continent, whereas B. j. japonicus migrated within the Japanese Archipelago. Lastly, the summering range of B. j. burmanicus did not overlap with that of B. j. japonicus. Our results suggest that the migratory directions and breeding ranges of B. j. burmanicus and B. j. japonicus are divided along the Sea of Japan. We inferred that the presence of the Sea of Japan and the migratory behaviour of soaring raptors to avoid crossing a large, cold-water body may have prevented gene flow between them and caused endemism of B. j. japonicus in the Japanese Archipelago.