The Cormorant is a large, black, fish-eating bird with a long, hook-tipped bill. They can be seen on both coastal and inland waters. When on water they swim low with their bill raised, and often dive with a leap from the water's surface. Their plumage is not waterproof but this has the advantage of allowing them to dive deep, as buoyancy is reduced.
Telling apart from Shag
Inland population expansion
Historically, the Cormorant population in the UK and close continent has been kept at a low level due to persecution by humans and through reduced breeding success (in the 1950-60s) as a result of pesticide pollution.
Following protective legislation against persecution in Denmark and Holland in the 1960s, the European population increased rapidly and continental birds started to extend their wintering range into Britain & Ireland.
Cormorants are now widespread throughout Britain & Ireland with the highest densities on the coast, at estuaries and on inland waters.
The Cormorant population has decreased in Scotland, northeast and southwest England. However, there has been a steep increase inland in England and in regions bordering the northern part of the Irish Sea.
- 53% range expansion since 1981-84 in Britain
- 18% range expansion in Ireland
- Population growth mainly in inland and lowland areas
- Wintering populations increased
Cormorant now found nesting in trees
In the UK the Cormorant was almost exclusively a coastal breeder until 1981, when an inland tree-nesting colony became established at Abberton reservoir in Essex. This colony was later found to comprise of Cormorants of the continential sub-species, P. c. sinensis. By 2012 Cormorants have bred at 89 inland sites in England, although breeding at many of these sites was of a single nest or did not persist.
Cormorant breeding colonies are now widely distributed across Britain & Ireland.
Cormorants build nests of seaweed, reed and twigs.One of the side-effects of nesting together as a colony is the volume of droppings, which over time kills the breeding trees.
Advantages of breeding inland
Research has found that the timing of breeding between the inland and coastal breeding birds is very different.
Coastal birds breed within a very narrow period, with all chicks all hatching at a similar time.
In contrast, inland Cormorants have a long breeding season. The large difference in timing of breeding within an inland colony, means that competition for food when chicks are large is reduced.
Whilst the Cormorant population as a whole in Britain & Ireland has increased in recent years, at a local level there are some very different trends.
Our native (P. carbo carbo) coastal breeding species has declined by about 11% since 1986, with some larger declines of up to 60% in northern Scotland.
In contrast, our recently established inland breeding population which is largely (but not exclusively) associated with the continental sub-species P. c. sinensis, increased rapidly following colonisation, but is now showing signs of stabilisation.
The UK holds an internationally important wintering numbers of Cormorant. Some British & Irish birds, particularly inland breeding P. c. sinensis disperse to winter on the continent.
The BTO is hoping to be able to look at the origins of Cormorants wintering on inland waters in England, to examine the potential impact of winter shooting on breeding populations.
Visit the BTO Mapstore to find out more about Cormorant populations.