Shags
Created | Updated Aug 11, 2008
The common cormorant, or shag,
Lays its eggs in a paper bag.
The reason you will see - no doubt
-It is to keep the water out!
But what these unobservant birds
Have not noticed is that herds
Of bears may come, with buns,
And steal the bags to hold their crumbs!..
- Christopher Isherwood
The Shag (Phalacrocorax aristotelis) is a dark-plumaged goose-sized long-necked aquatic diving bird with a characteristically long stout hooked bill, short wings, long tail and webbed feet. The Shag may be distinguished from its more gregarious cousin the Cormorant (Phalacrocorax carbo) by its size (the shag is smaller) and the fact that barring yellow patches at the base of its bill (its gape) and around its eyes it is all glossy-green dark whereas the Cormorant bears inter alia white patches on its face. Additionally, the reproductive Shag possesses a uniquely distinctive recurved crest which will be lost post-nuptially, but which may be used to identify the bird. A typical adult shag measures about 76cm (recorded range 65-80cm) long as opposed to a Cormorant which averages around 90cm.
The Shag’s habitat is exclusively marine, where it feeds on almost entirely on midwater fish (although occasionally bottom-dwellers including crustacea and molluscs), invariably by pursuit-diving from the surface, often with a slight leap into the air. Shags are usually solitary, especially in winter, although they may be observed in large groups albeit fishing independently.
Distribution extends to include the coast of northern and western Europe (including the whole of the British Isles, especially the north and west shores) from Iceland and northern Scandinavia south to Iberian Peninsula (Phalacrocorax aristotelis aristotelis); the Central Mediterranean eastwards to the Black Sea (Phalacrocorax aristotelis desmarestii); and the coasts of north-west Africa, especially Morocco (Phalacrocorax aristotelis riggenbachi). The Imperial Shag (Phalacrocorax atriceps encompasses severla subspecies common to islands of the Southern Hemisphere1. Whilst sightings have been reported in Belgium, Netherlands, Finland, Switzerland, Rumania, Israel, Iraq, Egypt, Malta and Germany, Shags usually stay within 100-200km of their breeding grounds.
Nests are constructed by both parents and typically consist of a base of bracken and seaweed, and are lined with grasses or other finer material. They are invariably sited on (preferably sheltered) rocky coastlines and islets, and in sheltered bays, although birds do occasionally venture off to sandy or muddy estuarine shores, or (exceptionally) inland.
A standard Shag clutch can be between one and half-a-dozen eggs, with three, the average. If lost, a replacement clutch will be laid. Incubation by both parents lasts 30-31 days (usually starting after deposition of the second egg), whereafter asynchronous hatching occurs. Chicks are at once altricial and nidicolous2, and are necessarily cared for and fed (by direct-bill partial-regurgitation) by both parents. After the juveniles fledge, typically at about 53 days after hatching, parental care can continue for 15-20 days, although records indicate that this period has in some cases been extended to 50 days or more. Juveniles are mature enough to recommence breeding at three, although more commonly four years old.
Breeding pairs are usually seasonally monogamous; and this pair bond may be maintained in successive seasons, particularly if breeding is successful. Simultaneous "bigamy" (polygamy) can occur, particularly where nesting sites are limited.