Cormorant (Phalacrocorax carbo)



Cormorant © Richard Steel

Cormorant © Richard Steel

After years of hanging about in the county, occasionally building nests that came to nothing (including a pair laying eggs on a platform at Fiddlers Ferry in 1999), Cormorants marked the start of this Atlas in 2004 by their first successful breeding in Cheshire. Amazingly, this happened simultaneously at four widely-spaced sites – Frodsham Marsh, Fiddlers Ferry, Rostherne Mere and Trentabank Reservoir. What triggered this breeding is not known, but it seems that they just needed that stimulus, and three of these sites now host significant colonies.

The Cormorant was almost exclusively a coastal breeder in the UK until 1981, but has since established colonies in many inland areas of England. The species account in the ‘Seabird 2000’ book (Mitchell et al 2004) seems especially prescient, concluding with the comment ‘Many of these new inland colonies have been established at sites used as winter roosts. Given the large number of roost sites and the availability of suitable feeding areas nearby, further expansion of the inland-breeding habit in England (and beyond) seems inevitable.’ All of the Cheshire breeding sites indeed hosted substantial winter roosts, and at Frodsham and Trentabank there is a clear association with an established heronry.

There has been much speculation about the origins of the birds, and it is impossible to mention breeding Cormorants without hearing the word ‘sinensis’. Cormorant is a cosmopolitan species, breeding in every continent except South America and Antarctica, with probably six races/ subspecies (HBW). The nominate race carbo nests on rocky cliffs from eastern North America, through Greenland and Iceland to the British Isles and Norway. The sinensis race is found from China (as its name implies) through India and across continental Europe where they usually nest in trees. Sinensis are smaller and greener in colour, normally with more white on the throat and with more filoplume feathers on the neck, but there is much individual variation and some old carbo show a lot of white on the head, so racial attribution on the basis of appearance or behaviour is not as straightforward as some birdwatchers believe.

Cormorants have occasionally nested inland in Britain for centuries, but this habit really took off in 1981. In the quarter-century to 2005, breeding had been recorded at 58 inland sites, and the inland population rose to at least 2,096 pairs, exceeding the coastal total of 1,564 pairs (Mitchell et al 2004, Newson et al. 2007). Detailed study (Newson et al. 2007) at colonies in eastern and central England, including observations of colour-ringed birds and DNA sampling, suggests that inland breeding has probably been sparked by birds of the continental race sinensis from the Netherlands and Denmark, but many carbo chicks from coastal colonies in Wales and England have also moved to inland sites to breed. The proportion of carbo increases in longer-established colonies, suggesting that inland colonies might be founded by sinenis but more and more carbo thenjoin them. Cormorants are faithful to their natal colony, but as a site nears its carrying capacity an increasing proportion of mostly younger birds breeds elsewhere, either by moving to existing colonies or founding new ones.

Although Cheshire’s nests have not been studied, Cormorants normally lay 3 or 4 eggs and the parents share incubation for 28 - 31 days. Chicks are in the nest for around seven weeks before fledging. Research elsewhere shows that inland-breeding Cormorants achieve significantly higher rates of productivity (2.3 to 3.0 chicks per pair) than coastal breeders (1.8 to 2.4) (Mitchell et al 2004). Some more in-depth study of the Cheshire colonies would be valuable, including searching for rings or colour-rings on the adults, monitoring the productivity of the nests, taking DNA samples from the birds and observations of food items.

The map appears somewhat to exaggerate their status because the nests at Frodsham span three tetrads. Birds often display, carry sticks and occasionally build nests in years before they successfully establish a new breeding site, so all such observations are worth recording. This survey found birds displaying in trees next to the River Weaver (SJ65T). There are also records of non-breeding Cormorants from many waters in Cheshire. They normally start breeding from the age of 3 to 5 years (occasionally 2), so there are many immature birds present all summer.

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