The affect on my Japan list was two steps forward one step back. Not unlike trying to get to grips with these birds on migration. I've sought out migrants locally over the last three autumns and am coming to the conclusion that there is probably only one taxon passing through the Kyoto city area. But which? Japanese Leaf is the closest breeder but generally Japanese summer visitors leave early, September sees a mass exit of other warblers, the cuckoos, Asian Brown Fly peaks then, and so on. In October non-native Grey-streaked Flycatcher and "Arctic Warbler" are the commonest migrants in Kyoto. So are these later migrants Kamchatka Leaf? I suspect they are, certainly the calls match.
At the moment vocalisations seem the only safe way identifying these warblers but because Japanese Leaf Warbler doesn't breed around Kyoto I'm not as familiar with their calls as might be expected for a long-term Japan resident, it's only in October when birds are passing through that I get to hear calls regularly, and as I said I believe these are Kamchatka not Japanese. Morphologically I don't see anything different about these birds either.
I get out to Hegurajima most Octobers and, though I'm not as focused on the complex there, I check all the birds that cross my path. The vast majority look and sound the same as those in Kyoto but it is only on the island that I do see and hear variation. This gives me more confidence that I'm not overlooking anything in Kyoto and that there really is just a single common autumn taxon passing through.
The following images are of four presumed Kamchatka Leaf October migrants in the Kyoto city area.
In neutral light, even if viewed from below, it's usually possible to see the sides of the breast are extensively grey. This runs along the flanks and narrows across the centre of the breast. The yellowish throat, belly, vent and undertail coverts are most obvious head on or from below. Viewed from the side the underparts look predominantly grey.
Obviously yellow centrally below when viewed head on, but much greyer from the side. The bill is quite long and strong with a slightly decurved tip to the upper mandible.
While most Hegura birds looked basically the same as the previous birds there have been some that differed. I've heard three birds which must have been Japanese Leaf but of the two of them I saw I couldn't get meaningful views. Below are images of two birds I've seen on the island which look rather different to the the usual birds I see.
This bird has a slighter feel to it, it looks paler and brighter lacking the dirty underparts. The sunny conditions may play some part comparing images.
The bill is shortish and spiky without the curved tip. The supercillium is straighter and narrower, it lacks the bulge above the lore and doesn't flare at the rear. Eyestripe is narrow. Rear flanks hint at greenish-grey rather than dirty-grey. Vent and undertail coverts white.
Another large, strong warbler. Very green above, it doesn't seem to have the greyish cast. Ear coverts also rather green. 10 October 2013.
Not so clear in these low resolution images but the p2 tip appears to be level with that of p6. This is the only shot I have showing the relative position of this primary tip but on all the presumed Kamchatka I've seen the p2 tip consistently falls close the tip of p5, there is a strong indication of this in the shot below. Both these shots were in overcast conditions so the apparent difference in upperparts colouration should be a reasonably honest reflection in these two sharpened but otherwise unaltered images.