Whatever the reason, (imagination/environmental context/genuine differences between subspecies or individual birds) this was certainly the case to my eyes. I had very close views of modesta (it seems) here and equally have had very close views of alba in the UK very recently before arriving to Japan, and to my eyes the difference in size was very apparent (hence the intermediate egret confusion).
Certainly been an an interesting learning curve with egrets for me! Appreciate the info.
I am adding some further comments and photos just to complete the thread, or at least make it more information-rich.
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Preface: I said in my original reply to James that Intermediate is a summer bird and summer is over. What I should have said is that in May/June/July they are around and breeding, and I don't see them later, but in September we still get a few (and locally a lot) of migrating individuals from further north - so, if it seemed that my comment suggested he
couldn't have seen Intermediate last week, then I apologise.
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The Japanese for these birds translates as 'Big Egret', 'Medium Egret' and 'Little Egret'. (I translate as 'Medium' because 'Intermediate' seems to more directly reference the bigger and smaller versions than the Japanese does.)
In my area, at least, if necessary when both are present, among birders
alba is 'Big Big Egret' and
modesta is 'Medium Big Egret'. As I said above,
alba has become increasingly common in winter in recent years and where it was once something to get excited about, it no longer is particularly special.
Referring back to Butty's important point in #6, in our area, difficulty in judging an individual bird by size arises as a problem with differentiation between
modesta Great and Intermediate in the summer, and this is when the 'eyeline test' is useful;
alba is so much bigger than Intermediate that it would not be a problem.
I attach a few photos to illustrate.
Photos 1 and 2 show two Intermediates with a
modesta Great.
Points to note:
The 'kink in the neck' theory of differentiation doesn't hold - both species can do both, although perhaps not as often as each other.
In the field at a certain season, the size difference, as Butty correctly says, is not apparent when only one species is present (and even then, crouching and general posture, especially when the birds are far away, can cause problems).
Photo 3 shows modesta Great on the left, Grey Heron in the centre and Intermediate on the right.
Photos 4 and 5 show the eyline of the Great and Intermediate.
Points to note:
Mark Brazil's 'Birds of East Asia' says that
modesta is slightly smaller than Grey Heron, and
alba is slightly bigger, in general. This seems reasonable. The Grey in this photo is several metres in the background and the
modesta in the front.
Again, the kink in the neck theory doesn't hold, as the bird on the right is Intermediate.
Looking at photos 4 and 5, even the eyeline can be difficult to use, as I said in my first post in this thread. While the Intermediate is obvious, the eyeline of the
modesta Great is not so evident on this individual, because of wind/water or whatever, so if we saw just this bird it might not be evident which it was of Great or Intermediate. But with the larger picture available, we can make these judgements.
This post isn't challenging or supporting any other posts; I simply hope it provides some food for thought.
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Postscript
I'd like to thank John Allcock for his post #9. Over the years, he has helped me a lot through his posts from near but not-the-same HK
