Great Cormorant

Great Cormorant Phalacrocorax carbo (Linnaeus, 1758)

North Atlantic Cormorant Phalacrocorax carbo carbo (Linnaeus, 1758)

(Probably a common resident that occurs in all months)

Eurasian Cormorant Phalacrocorax carbo sinensis (Blumenbach, 1798)

(Probably a common resident that occurs in all months)

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."

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 Phalacrocorax carbo 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 have been made available since 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.

Bibliography (sources of information)

  1. British Ornithologists' Union (BOU) website
  2. British Trust for Ornithology (BTO) website
  3. Newson, S., Marchant, J. Sellars, R., Ekins, G., Hearn, R. & Burton, N. Colonisation and range expansion of inland-breeding Cormorants in England. Brit. Birds 106: 737-743, Dec. 2013.

Updated 8 December, 2013