Double-crested Cormorant

The double-crested cormorant is a member of the cormorant family of water birds. It is found near rivers and lakes and in coastal areas and is widely distributed across North America, from the Aleutian Islands in Alaska down to Florida and Mexico. Measuring 70–90 cm (28–35 in) in length, it is entirely black except for a bare patch of orange-yellow facial skin and some extra plumage that it exhibits in the breeding season when it grows a double crest in which black feathers are mingled with white. Five subspecies are recognized. It mainly eats fish and hunts by swimming and diving. Its feathers, like all cormorants, are not waterproof, and it must dry them out after spending time in the water. Once threatened by the use of DDT, the numbers of this bird have increased markedly in recent years.

Double-crested Cormorants are diurnal and spend much of their day alternating between foraging, resting, and preening. They are pursuit divers, using their powerful legs and webbed feet to chase fish underwater, often reaching depths of up to 7.5 meters (25 feet) and staying submerged for 30–70 seconds per dive. Their diet is primarily piscivorous, targeting a wide variety of fish species, but they may also consume amphibians and crustaceans. Foraging is typically solitary, though individuals may aggregate in areas of abundant prey. Socially, they are gregarious outside of feeding, forming dense colonies that can number in the thousands during the breeding season. Cormorants are known for their characteristic wing-spreading behavior, which is thought to aid in drying feathers and thermoregulation. They communicate through a range of guttural croaks, grunts, and hisses, especially at nesting sites. Roosting occurs communally in trees or on exposed rocks and structures, often near water.

Breeding occurs from early spring to midsummer, varying with latitude. Double-crested Cormorants are monogamous within a breeding season, with pairs forming shortly after arrival at the colony. Courtship displays involve ritualized posturing, bill clattering, and presentation of nesting material. Nests are constructed from sticks, reeds, and debris, often reused and enlarged annually. Clutch size ranges from 2 to 4 pale blue eggs, which are incubated by both parents for 25–28 days. Chicks are altricial, hatching naked and blind, and are brooded and fed regurgitated food by both adults. Fledging occurs at 5–7 weeks, though young may remain dependent on parents for several weeks post-fledging. High site fidelity is observed, with adults returning to the same colony and even nest site in successive years.

The Double-crested Cormorant exhibits several adaptations for an aquatic lifestyle. Its dense bones reduce buoyancy, facilitating deep diving. The partially waterproof plumage allows for easier submersion, though it necessitates frequent wing-drying. The hooked bill is specialized for capturing and holding slippery fish. Strong, webbed feet provide powerful propulsion underwater, while the tail acts as a rudder. Their keen vision, particularly adapted for underwater clarity, enhances hunting efficiency. Social nesting and colonial breeding provide protection from predators and facilitate information sharing about foraging locations. The species' broad ecological tolerance allows it to exploit a wide range of habitats, from freshwater to marine environments.

While not as prominent in folklore as some other water birds, Double-crested Cormorants have been both vilified and protected by humans. In North America, they have been the subject of management controversies, particularly regarding their perceived impact on fisheries. In some indigenous cultures, cormorants are recognized as part of the natural aquatic community. Globally, cormorants have symbolic associations with fishing, adaptability, and resourcefulness. Unlike Old World cormorant species, the Double-crested Cormorant has not traditionally been used for fishing by humans.

Recent research has focused on the ecological impact of expanding cormorant populations, particularly their interactions with fish stocks and nesting habitat selection. Studies using satellite telemetry have revealed long-distance dispersal and migration patterns, with some individuals traveling over 1,000 km between breeding and wintering grounds. Genetic analyses have clarified subspecies boundaries and population structure, supporting the recognition of five subspecies. Ongoing investigations examine the effects of environmental contaminants, such as mercury and PCBs, on reproductive success and chick development. Behavioral studies have explored the function of wing-spreading and social foraging dynamics. The species is also monitored as a bioindicator of aquatic ecosystem health.

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The Double-crested Cormorant is currently classified as Least Concern on the IUCN Red List.

Historically, Double-crested Cormorant populations declined sharply in the mid-20th century due to the effects of DDT and other organochlorine pesticides, which caused eggshell thinning and reproductive failure. Since the ban of DDT, populations have rebounded dramatically, leading to new challenges. In some regions, cormorants are perceived as competitors with commercial and recreational fisheries, resulting in culling and nest destruction. Habitat loss, disturbance at nesting colonies, entanglement in fishing gear, and environmental contaminants remain ongoing threats. Despite these pressures, the species is currently classified as Least Concern by the IUCN, with stable or increasing populations across much of its range. Localized declines may occur due to human disturbance or habitat alteration.