However, recently conducted research outlined differences between Hokkaido’s Shima Enaga and their mainland counterparts. Of all the Aegithalos caudatus sub-species, the Shima Enaga (Aegithalos caudatus japonicus) are sub-regionally endemic to Hokkaido, but, due to their limited isolation from their mainland cousins, they have developed certain distinguishing features that are pronounced enough to call them a completely different subspecies of the Shima Enaga. But what sets them apart? The first thing is the length of their tail fork; it's overall longer than the other subspecies. The second is a marginally shorted tail overall when compared to the mainland counterparts of the Shima Enaga. The third is a more rounded wing, and the final feature is darker tertiary flight feathers which are difficult to see when the bird is not in flight. Even Shima Enaga of the Sakhalin Islands off the coast of Russia are more similar to their mainland and continental counterparts. The Shima Enaga I have the pleasure of photographing during my annual Hokkaido Birding Exploration Workshop Japan photo tour are absolutely a subspecies all their own.