Continental race of Cormorant - Ogston Reservoir

Spent this morning sat in the hide at Ogston, whilst the rain continued outside. My only diversion was the Cormorants sat in front of the hide. Two were white headed adults showing characteristics of the continental race sinensis. I took quite a few photos then, when I got home, thought I would check for the latest thoughts on separation of nominate carbo from the continental race sinensis, I knew most of the obvious field characters; extent of white on the head and flanks and plumage colouration had now been discounted as unreliable but knew there was something about the gular pouch angle.

Continental Cormorant Phalacrocorax carbo sinensis

The most detailed analysis on the subject was published back in 2004 (Sub-Specific Differentiation & Distribution of Great Cormorants in Europe Stuart E. Newson et al). The study concluded that a bird with a gular patch angle <65 degrees was likely to be P c carbo and those with an angle > 73 degrees was probably sinensis. 
The bird photographed today at Ogston looks to have an angle of 90 degrees and is probably therefore the continental race sinensis

Comparison of gulag patch angle in P c carbo and P c sinensis

For comparison the photo below is of a bird photographed at Chatsworth last November, it is bearing a ring which identifies it as having originated from Rutland Water. The gular pouch angle is around 60 degrees which accords with it being the nominate race carbo although it should be noted that the number of sinensis has increased in the inland breeding population during the past few decades.

Cormorant P c carbo