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Double-crested CormorantDouble-crested Cormorant
On many a coastline or inland waterway throughout North America, one can often see the distinctive silhouettes of Double-crested Cormorants—riding low on the surface, flying with oddly bent necks, or resting with wings spread. Highly gregarious, this species is the only cormorant commonly found in the interior of the United States and Canada.

Double-crested Cormorants breed in the Aleutian Islands and on the southern coast of Alaska, and on parts of the Pacific coast of Washington and Oregon, as well as San Francisco Bay, California. The breeding range of the species also includes appropriate habitat in the Rockies and the plains states and provinces, from Saskatchewan to western Ontario and from northern Utah to the Great Lakes, as well as coastal regions from Quebec to Long Island, New York, and much of Florida. Double-crested Cormorants also breed in Cuba and in Baja California.
Double-crested Cormorant Range Map

Migration is highly variable among different populations of Double-crested Cormorants. Those that nest in the interior of the continent do migrate, probably to California and Mexico, while those that breed on the Great Lakes and the north Atlantic coast winter along the Gulf of Mexico, in the lower Mississippi River valley, on the mid-Atlantic seaboard, and in the Carolinas. Alaskan Double-crested Cormorants apparently winter off the coast of southern British Columbia. Other populations remain resident year-round.

Double-crested Cormorants feed almost exclusively on fish, representing more than 250 species from more than 60 families. In general, these fish are small, and move slowly or in schools. Double-crested Cormorants feed close to shore in relatively shallow water, diving from the surface and propelling themselves swiftly with their feet. They seize fish in their bills; both mandibles are hinged, allowing for a very wide gape. Upon capturing a fish, Double-crested Cormorants may eat it under the surface, or if it is large and unwieldy, may bring it to the surface, where the bird may shake the prey, whack it on the water's surface, toss it into the air, and swallow it, head first.

Double-crested Cormorants commonly stand on a branch, rock, or structure and spread their wings after swimming. This behavior probably functions primarily as a means to dry feathers, but the value to the species of drying is not entirely clear. Wet wings apparently do not appreciably compromise flight, nor does drying appear to serve a critical thermoregulatory purpose. Double-crested Cormorants spread their wings at rest on cloudy days, or even in light rain, as well as in sunshine.

Double-crested Cormorants are highly gregarious year-round. They nest in dense colonies, in trees or on sloping cliffs. They sometimes forage in large numbers together, at concentrations of fish, and rest at common sites during the day. Migrating Double-crested Cormorants move together in sizable, loosely V-shaped formations, usually very high in the sky. Outside the breeding season, they form nocturnal roosts numbering in the hundreds or thousands.

Paired males and females build the nest together, often using nests from previous years or old heron or egret nests as a foundation. The male collects sticks and brings them to the female, who builds the nest and actively guards against theft of nest material by other cormorants. Both sexes continually add material to nests throughout incubation and the early stages after hatching; such accretion, combined with multiyear reuse of nests, sometimes results in nests more than 6 feet high.

Clutches, on average, include four eggs. Both males and females incubate, switching off every one to three hours. When incubating, Double-crested Cormorants position their eggs on top of their feet and settle on them with their bellies. Upon hatching, chicks are blind and essentially helpless. Parents tend new hatchlings equally, forcing partially-digested food particles into the mouths of their offspring. Beginning a few days later, nestlings can take whole fish, which the parents deliver by lowering their mouths over the entire head of a young bird. Young Double-crested Cormorants leave the nest after about three to four weeks, but remain near the nest site until they achieve the ability to fly, approximately three to four weeks later.

Double-crested Cormorants are large, dark aquatic birds, measuring about 32 inches in length. Adult plumage is black, sometimes with a greenish or bronze-colored sheen. Bill has a distinctive, pronounced hook at the tip of the upper mandible. Bare skin on face and throat is bright orange-yellow. Iris is a brilliant turquoise. Breeding birds have small whitish plumes above each eye. Juveniles have grayish necks and breasts. Cormorants fly with their necks extended, but with a small, distinctive double-kink.

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