The common cormorant or shag
Lays eggs inside a paper bag.
The reason you will see no doubt
It is to keep the lightning out.
– Christopher Isherwood (1904 - 1986)

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 unique and distinctive recurved crest which is lost post-nuptially, but may be used to identify the bird. A typical adult shag measures about 76cm (recorded range 65-80cm) long. The cormorant averages about 90cm.

The shag's habitat is exclusively marine. It feeds almost entirely on mid-water 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.

Their distribution extends to the coasts 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 the 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 several subspecies that are common to islands of the southern hemisphere¹. While sightings have been reported in Belgium, the Netherlands, Finland, Switzerland, Romania, 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, lined with grasses or other finer material. They are invariably sited on (preferably sheltered) rocky coastlines and islets, and in sheltered bays. Birds occasionally venture off to sandy or muddy estuarine shores, or (exceptionally) inland.

A standard shag clutch is between one and half-a-dozen eggs, with three being 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). Thereafter asynchronous hatching occurs. Chicks are at once altricial and nidicolous². They need to be cared for and fed by direct-bill partial regurgitation by both parents. After the juveniles fledge, typically about 53 days after hatching, parental care can continue for 15-20 days. Records indicate that this period has in some cases extended to 50 days or more. Juveniles are mature enough to commence breeding at three years of age, although it is more commonly nearer four.

Breeding pairs are usually seasonally monogamous. This bond may be maintained in successive seasons, particularly if breeding is successful. Simultaneous 'bigamy' (polygamy) can occur, particularly where nesting sites are limited.