Great Cormorant - Blagdon Lake Birds

Great Cormorant Phalacrocorax carbo (Linnaeus, 1758)

Overspill, Blagdon Lake © Nigel Milbourne 2009

The identification of the two sub-species is best made in the field by judging the angle of the rear edge of the yellow gular patch as described in the article by friend Keith Vinicombe given in the bibliography below. An acute angle is a carbo, and an obtuse angle would be a sinensis. It is, nevertheless, a challenge, as illustrated in the series of three photos of a swimming Cormorant in the gallery below, taken over a period of five seconds. You need to try and judge with the head held level and side on. A square block of yellow skin below the gape is indicative of sinensis.

Click on an image to enlarge it.

Note navigation arrows either side of, & slideshow option top right of, enlarged images.

No, it looks like a sinenesis after all.

Atlantic Cormorant Phalacrocorax carbo carbo (Linnaeus, 1758)

Fairly common resident. May occur in any month.

The earliest reports of Great Cormorants Phalacrocorax carbo at the lake that I have found so far were made by Donald Carr in the 1907 Report of the Wells Natural History and Archaelogical Society (incorporating the first report of the Mendip Nature Research Club). He wrote “Two were shot on Blagdon Lake in 1903, and four seen on lake May 1907.” In his subsequent list, dated 30th November 1908, he wrote “now a regular visitor during the year.”

Insert chart

Here is a chart of the regular winter WeBS counts made since 1986-87 with each winter presented as an average of the counts made from October to February inclusive, with the first winter period plotted against the x-axis viz. winter 1986-87 is shown against 1986 on the x-axis. I have superimposed the winter WeBS maxima (Sep.-Mar.).

There has been a lot written about the colonisation of inland waters by Great Cormorants since 1981, and it was established that continental birds P.c. sinensis played the more important role initially, though coastal-breeding birds P.c. carbo started to breed inland as well, and recent molecular work has shown that intergrades between the two races occur at English inland colonies to the point that distinction between the two sub-species is “becoming blurred” (Newson et al, 2013). The authors concluded that inland-breeding colonies continue to be established “most notably through expansion of their range into the south-west” which is not entirely supported by the maps that they present, in my opinion. Small colonies have been established in Wilts., Glos. and Som., but that seems to be part of a slow spread west that is far less marked than the range extension north through the Midlands. However, data for the period 2004-12 suggests the inland-breeding population has stabilised at about 2300 pairs.

Newson et al went on to say that there is an increasing tendency for coastal-breeding birds to winter inland and for continental birds to winter here too. Licences were made available from 1996 to control wintering Cormorants by shooting, to prevent damage to fisheries, but studies have shown that sites where control has taken place don’t show significant population changes year-on-year. It is also unclear what effect the control measures are having on the Cormorant population at a regional level.