Friday, April 15, 2022

Cold Edge

 'British' Cormorant, Phalacrocorax carbo carbo

The April 2022 issue of British Birds has an inspiring obituary of Ian (DIM) Wallace, written by Anthony McGeehan. It says that Ian deplored "the overlooking of subspecies". This makes sense, not least because subspecies are often elevated to full species, and if they have not been documented it is not possible to see population trends. It is good that The Calderdale List at the end of the Halifax report includes subspecies, (although 'Continental' Cormorant, P. c. sinensis, has yet to make it onto this list).

P. c. carbo and P. c. sinensis can only be separated by looking at the rear edge of the 'gular patch', the bare yellow skin around the proximal part of the bill. 

In carbo, the rear edge below the bill slopes forwards from the gape. This results in the angle between the rear edge above the gape and the rear edge below the gape being about 90 degrees - a right angle. See photos above.

In sinensis however, the rear edge of the gular patch drops vertically from the gape. This leads to the angle of the rear edge around the gape being an obtuse angle - perhaps 120 degrees.

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