Winter is the time of year to double-check those cormorants you see offshore. Perhaps what you took for granted as a flock of our resident Double-crested Cormorants is actually a group of the more northerly species, the Great Cormorant (Phalacrocorax carbo).
There are about 37 species of cormorants in the world, with six species occurring in North America. They have dark, glossy plumage, very long necks, long, hooked bills and webbed feet. The Great Cormorant is the largest of these diving water birds, reaching 35-40 inches in length with a wingspan of over five feet.
A cosmopolitan bird, the Great Cormorant is found in Europe, Asia, Africa, Australia and North America. In our part of the world its breeding range is limited to Greenland and the Canadian Atlantic to Nova Scotia, though its range has been expanding southward along the Atlantic coast. In the winter it will migrate to coastal waters as far south as the Carolinas and is rarely found inland.
How to tell the difference between a Double-crested and a Great Cormorant? The great cormorant is a larger bird, though from a distance size may be difficult to gauge. The browner juvenile birds of both species have a brown neck and breast, but the juvenile Great Cormorant has a white belly. Conversely, the juvenile Double-crested’s belly is dark, giving its brown neck and breast a pale look. An adult Great Cormorant will have a white throat patch below the base of its bill and the Double-crested will not. As the birds attain their breeding plumage around February, a white patch on the flank of the Great Cormorant will be a distinguishing field mark when the bird is in flight.
Cormorants feed by diving for fish. Great Cormorant are known to catch fish as large as 18 inches long, as well as 24-inch-long eels. They return to the surface with their catch to reposition it so that it can be swallowed headfirst. In Asia, the Great Cormorant was domesticated centuries ago by fisherman to catch fish for humans. Flocks of leashed cormorants are still kept today by Asian fishermen. A ring is placed around a bird’s neck before it is sent into the waters of the fishing grounds, thereby preventing it from swallowing the fish. The fisherman pulls in the leashed bird, removes the fish from its throat pouch and sends the bird back out. The hardworking cormorant is rewarded for its efforts when the ring is removed after several retrievals so it may catch a fish or two for itself.
Like all cormorants, the Great Cormorant’s feathers do not repel water as well as many other water birds’. It must regularly leave the water to allow its feathers to dry. Look for these winter visitors in trees, or on pilings and rocky islands as they gather to spread their magnificent wings to the winter air.