Mystery Murrelet
Returned to HK yesterday, sorry for our late response.
The only comment via the Oriental Birding E-group was kindly provided by Nick Lethaby, who wrote as follows: -
"I have spent a fair bit of time looking at specimens of these birds as
well as having seen a few dozen Japanese Murrelets in the field. One
feature that hasn't been mentioned is that on Japanese Murrelet, the
black at the base of the neck is more solid and extends a little on to
the mantle. In addition, Japanese Murrelets typically show extensive
black on the wing coverts whereas Ancient Murrelets are much greyer here
(although a few can be similar to Japanese in appearance). Although your
bird is very worn and messed up, it does seem to show these features as
well as the others that have been mentioned."
Other remarks by Nick Lethaby (via Birds Korea) have been reported by Peter and Michelle Wong above.
I suggest to wait one or two more weeks to see whether Mr. Koji Ono from Japan has any further remarks.
For the record, I'm still keen on Japanese Murrelet, despite the fact that it is very, very rare compared to Ancient. Due to the poor feather condition I think we'll struggle to differentiate most of the important plumage features, but the presence of the remains of a crest - which quite clearly comes from the forecrown - and the bill colour and shape, make me favour Japanese.
John