Cormorant

To dry their feathers. A cormorant's outer plumage is deliberately not fully waterproof; it wets through when the bird dives, which cuts its buoyancy and makes it easier to swim underwater after fish. The trade-off is that after a fishing session the bird is partly waterlogged and losing heat, so it hauls out onto a rock, post, or branch and holds its wings open, often facing the sun and wind, to dry the feathers and rewarm. The pose is so characteristic that a cormorant with spread wings appears on coats of arms and in heraldry. Other explanations, such as aiding digestion or balancing, have been proposed but the drying function is the best supported.

There is no consistent biological difference; both names refer to birds in the same family, Phalacrocoracidae, and which name is used is mostly a matter of local tradition. In Britain, the two common species are called the cormorant, a large bird of coasts and increasingly inland waters, and the shag, a slightly smaller, glossier, greener bird with a crest that stays out at sea on rocky coasts. Elsewhere, the smaller, often crested species, especially those of the Southern Hemisphere, are frequently called shags, and the larger ones cormorants, but the split is not scientific and some species are known by both names.

A fisher takes several trained cormorants out on a boat or bamboo raft, usually at night with a light to attract fish. Each bird has a soft cord or ring fitted loosely around the base of the neck, tight enough that it cannot swallow a fish above a certain size but loose enough to breathe and to swallow small fish as its own reward. The birds dive, catch fish, and are lifted back to the boat, where the fisher removes the catch from the throat pouch. The practice is centuries old on the Li River in China and on the Nagara River in Japan, where the imperial cormorant fishery is a protected cultural tradition, and today it survives mostly as a demonstration for tourists rather than as a commercial fishery.

It is contested. Cormorants are efficient fish predators and a large colony removes a substantial tonnage of fish from a lake or stretch of coast, so anglers, commercial fishers, and fish farmers frequently blame them for declines and lobby for culls. Scientific reviews generally find that cormorants take mostly abundant, small, non-target species and that their impact on the populations of prized sport and commercial fish is usually minor compared with overfishing, habitat loss, and pollution, though localised effects can be real, particularly at stocked ponds and fish farms where the fish are concentrated and cannot escape. Several countries permit controlled cormorant shooting or nest management, and the issue remains a flashpoint between conservationists and fishing interests.