chrisbrooks's picture

Great Cormorant

Observed: 2nd December 2012 By: chrisbrooks
Sea Fish AtlasSeaKeys
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Great Cormorant

It’s a Great Cormorant but hands up if you understand and can interpret gular pouch angles to determine the sub-species. Well this is my best shot of which I’m not certain. I measured the angle on this bird as 72 degrees; however this varied between 67 and 72 degrees depending on the angle of shot and which side of the head you chose.
These angles fall into the grey and overlapping area between the 2 sub-species and as far as I can ascertain a positive ID to that level is unsafe from a photograph. So for me, it remains as a Great Cormorant.

Species interactions

No interactions present.


Bill Henderson's picture

Gular Measurements


Ray Turner was kind enough to provide me with a reference:

which he claimed to be the basis for gular angle measurements in determining sub-species.

I read this paper carefully and was compelled to draw the conclusion that it is unsafe to attempt identification from data obtained from photographs. Now unless there has been subsequent research, I remain of the same opinion.

From memory:

Measurements were taken from the pelts of dead birds, and that
care had to be taken to arrange the birds before measurement.

Further, the populations studied were assumed to be of two distinct sub-species with no hybridisation. However, the authors did acknowledge that such hybridisation does occur and that they state that using such measurements may not be reliable in populations where hybrids do exist.

In summary:

Measurements from photographs are unreliable. Such measurements, if they could be made, should not be used in populations where hybridisation exists.

I have slipped into my asbestos underware and await the roasting :-)


Bill Henderson

chrisbrooks's picture


Hi Bill, I agree. I took about 20 images and the angle varied as described. Too many variables for me.