According to Leader & Carey (Forktail; August 2012) intermedia, occurring in north-east China, south-west Russia and the Korean peninsula, is morphologically distinct from the Japanese cyanomelana. The latter having pure glossy black throat, breast as well as ear coverts and lores whereas intermedia "...are matt-blackish on the throat, breast and ear coverts (only very rarely pure black), and usually show a bluish wash or distinct blue tones to the throat and breast."
I always check Blue and White in migration hotspots, aware of the possibility of finding an intermedia or better still a Zappey's, but only rarely during the breeding season within normal range. Not least because the birds sing from tree tops and views don't often allow close scrutiny. However I had excellent, if brief, views of a bird in central Kyoto prefecture last week that is also surprisingly blue breasted. At first the bird was seen low in the trees giving an opportunity to observe it more closely than is often the case but it was nevertheless against diffuse understorey light and didn't raise any red flags. When it came down to ground level into some tree roots on the steep hillside next to the track and then into low bushes it was far easier to judge the true colour of the bird. It was then that it began to look somewhat atypical. Unfortunately it soon flew further back into the trees and I wasn't able to spend longer looking for it.
The first thing worth considering is that the greater coverts clearly indicate this is a 2CY bird and I wonder if this may be the reason for its much bluer than normal appearance. Do 2CY males look different to adults? Another interesting feature I didn't notice in the field but is apparent in the images is that the back has a slightly more turquoise tint than normal Blue and Whites I see in Japan, this is more of an intermedia feature, and it's quite obvious where there is a very clear-cut division between the lower back and deeper blue of the lower rump and uppertail coverts. This could be more apparent because the neutral light allows a clearer assessment but I don't think that's the case. Could it then be another potential feature of young males?
I confess that for years I've been guilty of ignoring Blue and White's on the breeding grounds other than to enjoy the stunning appearance of birds that happened to be, like this one, closer than usual. However there now seems reason to give these easy-to-ID inland Blue and Whites a second look rather than simply appreciating their beauty.
Questions that spring to my mind are do 2CY males look different to adults, closer in appearance to intermedia, if so then do 2CY intermedia also look any different to adults? How might this affect identification of spring migrants on off-shore islands where intermedia might be more likely to occur? Might some intermedia pass through mainland Japan on a broad front just as Grey-streaked Flycatcher does? Unnoticed because of their similarity to the local taxon which ostensibly doesn't present any identification challenge.
When the bird dropped lower and the sloped forest floor became the backdrop the subtle colouration became more apparent.
|It seems the angle and lighting play a part. Here the throat looks a dull matt-black faintly washed blue, perhaps still closer to intermedia than to cyanomelana. Note the distinct division between the back and lower rump / uppertail coverts.|
|It has a strikingly blue face in this image with black restricted to the lore and chin. The border between nape and ear coverts has all but disappeared - this looks extreme. Below is a more heavily cropped version.|
|A typical Blue and White at the same location. Of course the lighting is very different but there's no hint of contrast on the upperparts.|
|A typical spring cyanomelana with a glossy black throat and distinct black and blue border down the neck.|
|Another example in late April this year. Again the glossy black throat and blue / black contrast are obvious.|
|An October 1CY male. If the adult-type back feathers are acquired much earlier than rest of the upperparts might later grown feathers be a different shade and account for the colour contrast between back and rump?|
It seems there are still reasons to keep looking closely at Blue and White Flycatchers.