Double-crested Cormorant

Belonging to the Cormorant family, the Double-crested Cormorant is a fascinating species indeed. Their distinctive features such as their titular double-crested feathers and their piercing turquoise eyes become prominent only during the breeding season. For this reason, you may not be able to use only their crests to identify them other than for a few months a year.

About Double-crested Cormorants

Double-crested Cormorants have five known subspecies, two of which are known to be resident birds and non-migratory. All subspecies are known to be largely silent. These birds can commonly be seen drying their wings after a swim, in a grand, dramatic fanning of their wings.

Let us not waste any more time! You must be itching to learn more about these beautiful birds. In this article, you will learn about:

● Double-crested Cormorant Photos, Color Pattern, Song
● Double-crested Cormorant Size, Eating behavior, Habitat
● Double-crested Cormorant Range and Migration, Nesting

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Double-crested Cormorant Color Pattern

Fully grown Double-crested Cormorants have covers that run dark brown to black, with a duo-chrome-esque gloss of muddy green or bronze. When the plumages are worn, this sheen wears off. They have also been described as full Blackbirds. They gain their black and white double crests only during the breeding season.

Double-crested Cormorants have orange-yellow skin on their faces and throats that stay prominent year-round. Adult bills have a black upper mandible, speckled with grayish to dull yellow on the sides. The lower mandibles are yellowish-brown.

Adult irises are a striking bright blue-green or turquoise during breeding season, bordered by a thin scintillating green ring. The shades of blue-green vary according to geographic population. The rest of the year, adults have black irises.

Juvenile Double-crested Cormorants have a duller color pattern. Their upper breasts are paler, and their bellies are darker. Double-crested Cormorants heads are usually a grayish dark brown or pale brown, gradually becoming grayish white till their chins. Their throats are mostly white with specks of brown. The coverts of their upper wings and upper parts are a dark grayish brown, with dark margin feathers that create a scaly impression on the human eye. Their lower backs and rumps are a richer gray-brown. Juvenile plumages lack the duo-chrome like gloss of the adults.

Juveniles also have dark brown upper mandibles that fade into a paler hue on the lower mandible. They also have brown irises.

Description and Identification

These birds are described as gangly, scaly, even prehistoric-looking due to their unique eyes, crests during the breeding season, and curved upper mandibles that cover their lower mandibles. They have also been described as a combination of a Goose and a Loon.

They are likely to be sighted around fresh and saltwater bodies across the continent of North America. Double-crested Cormorants are not waterproof birds, so they are often spotted drying their wings on docks or rocky islands by spreading them out dramatically.

These Cormorants are relatives of frigate birds and boobies. They have large bodies, long, slender, necks, and long tails. They also have long bills with small hooks on the tip, which they position tilted upwards while swimming.

While all North American cormorants inhabit coastal areas, these are the only ones that can be found deeper in the iNlands as well. This is a great distinguishing to keep in mind whilst trying to identify them.

They can be confused with the Great Cormorant which breeds in similar locations, but the latter is larger than the former on average. Great Cormorants also have striking white patches of feathers on the back of their heads. The juvenile members of these two species are almost identical, but the Double-crested Cormorants have pale throats and breasts with darker bellies, as compared to the Great Cormorant young ones, who have dark throats and bellies with paler bellies.

In Southern America, Mexico, and the Caribbean, these birds can be confused with Neotropic Cormorants, especially after they have dispersed following breeding activities. The Neotropics are smaller and slenderer, with longer tails. Their throat pouches are also different in shape and color than Double-Crested Cormorants, the gular pouches of the former form a horizontal V shape, and are pale yellowish-brown, outlines by a thin line of white feathers ending below the eye. In contrast to this, Double-crested Cormorants have much larger, rounded pouches that are brighter in color.

Here again, the juveniles are difficult to distinguish from one another. Keep in mind that Double-crested Cormorants have brighter supraloral skin or the skin between the eyes and the bill. Immature Neotropic Cormorants are more evenly colored than young Double-crested Cormorants.

As mentioned earlier, other species of Cormorants stick to the coasts almost exclusively. The Red-faced and Pelagic Cormorants might be mixed up for Double-crested, but are smaller and slenderer, with red facial skin and gular pouches. Breeding members of the former two species have white patches on their flanks. Brandt’s Cormorants are of the same general shape and size as the Double-crested Cormorants, but they can be easily distinguished by their less prominent, blue-violet hued gular pouch, with a short band of buff-colored feathers behind it. Immature Brandt’s Cormorants are usually darker than young Double-crested Cormorants.

In contrast to the Common Loon, Double-crested Cormorants have hooked bills, which are usually tilted upwards.

Double-crested Cormorant Song

Double-crested Cormorants are not extremely noisy birds, and in certain populations are considered almost entirely silent.

In their nesting colonies and roosting spots, they make deep, guttural, grunt-like calls. In their breeding colonies, they have been observed making “t-t-t-t” sounds before taking off for flight, and “urg-urg-urg” sounds while landing.

Sexual displays are done by adult male individuals with “ugh” or “ok-ok-ok-ok” sounds which are considerably loud.
When threatened, they emit “eh-hr” notes repeatedly.

Juveniles beg their parents for food by chirping. They also chirp when they are distressed by heat, and hiss in defense in the face of danger.

Double-crested Cormorant Size

The average length of adult Double-Crested Cormorants is 32 inches, and their average wingspan is 52 inches. However, they vary widely in dimensions across subspecies, so there is a large coefficient of standard deviation. In mass, they can be anywhere from 1-3 kilos or 2.2-6.6 pounds.

Double-crested Cormorant Behavior

While resting, Double-Crested Cormorants maintain a pose that is almost vertical. Their necks hold an S-shaped posture and their bill tilts upwards. They also tilt their bills like this in the water.

They are less graceful on land, presumably owing to their short legs. Double-crested Cormorants walk with a clumsy, waddling gait, intermittently hopping with both legs. They waddle in an upright position. They use their bill hooks to grip onto rocks or other surfaces while climbing upwards. Double-crested Cormorants readily perch onto branches and other elevated surfaces, even the masts or riggings of boats, or overhead wires.

Unique to a seabird, the Cormorant family members have short wings of a low aspect ratio, enabling them to cruise at high speeds. However, they do not have enough strength to lift even moderate loads, so they have to forage within smaller ranges and bring small portions of food incrementally for their young ones. They crook their necks while flying. In flocks, they form a V-formation, similar to Geese.

These birds enjoy swimming but do not stay in the water after they are done with a swimming session. They often look for prey underwater. Their main propelling force is their feet, as their wings are too heavy to push them forward. The Double-crested Cormorants’ eyes are adapted to allow them sight above and below the water.

Their feathers are wettable, which is the primary motivation behind their feather-fanning rituals. The ability of their feathers to get wet has been theorized as an evolutionary adaptation for diving. We do not know if wet feathers hinder flight. Adults sleep in a standing position. They may rest their necks vertically on their backs and tuck their bills into their underwings. In cold weather, they tuck their feet into their flank feathers.

Double-crested Cormorant Diet

These Cormorants have a diet comprising primarily of fish and other aquatic prey that can be found in their habitats. Their diets can consist of crab, shrimp, frogs, eels, crayfish, and salamanders as well, depending on their availability. They also enjoy mollusks, snakes, and plants. Insects and amphibians have also been recorded to be staples. Cormorants in general are known to eat baby ducklings, and will eat an entire clutch of eggs in one go!

An adult Double-Crested Cormorant eats an average of one pound a day. They mostly forage by diving to find underwater prey. They forage alone and in groups.

Double-crested Cormorant Habitat

These birds inhabit a wide range of marine habitats across seasons. Non-breeding populations are scattered widely. Breeding birds on the inlands spend the winters in coastal regions. These birds require spots for feeding, roosting, and loafing.

During the breeding season, they inhabit aquatic habitats such as ponds, lakes, artificial impoundments, slow-moving rivers, lagoons, estuaries, and open coastlines. They spend the winter (non-breeding) along southern coasts for their relative warmth.

Range and Migration

Spring Migration from the Gulf of Mexico begins as early as February, and these birds follow the Atlantic coastline and go overland. They reach their destinations Oklahoma or Virginia by early March. The rest of the birds reach their destinations by late April at the latest.

Fall migration is essentially the reverse movement but begins well in advance of the water providing resistance. This migration is also much quicker. The average departure date across geo-specific populations was the first of October.
Females may begin their journey earlier than males.

There are also resident, non-migratory sections of this species. P. a. floridanus in Florida and the Caribbean are largely resident. P. a. heuretus in the Bahamas is also likely a non-migratory population.

Double-crested Cormorant Lifecycle

After hatching, the nestlings remain in the nest for 3 to 4 weeks, after which they may wander around the nesting colony, but return to be fed. They fledge at about 5 to 6 weeks and become fully independent at around 9 to 10 weeks.

They usually begin breeding at 3 years of age. The average lifespan of Double-crested Cormorants is 6 years, but they can live up to 22!

Nesting

They establish colonies away from any potential ground predators and close to areas with promising leads of food. This can include small islands, or manmade structures like bridges, abandoned ships, docks, etc.

They nest in colonies, sometimes mixing with other species. Males splash water on their female partners with their wings. Other displays include zigzag swimming, bringing their partners weeds, and diving.

They lay 3-4 eggs in one clutch usually but have also been recorded to lay more. The eggs are bluish-white, and their nests stand them. Both sexes incubate the eggs for a period of 25 to 33 days. Both parents feed the young nestlings.

Anatomy of a Double-crested Cormorant

They are large birds resembling the anatomy of other Cormorants and the Common Loon. They have broad, rounded wings with ulna and humerus of roughly equal lengths. Their external nostrils are permanently closed after maturing.
While swimming, we can see their hindlimbs and large totipalmate feet behind their body. Their leg muscles make up only 5% of total body mass.

Final Thoughts

In conclusion, Double-crested Cormorants are incredibly fascinating birds. Areas of research that can be prioritized are the diverse characteristics between subspecies, a coordinated census of all their populations, and the significance behind the colors of their facial features.

Although they are not of high concern on the conservation front, these birds have been extensively exploited by economic activities. Their habitats have been destroyed by commercial impinging of the coasts, and they have been killed for food and commercial use. Cormorant eggs are historically known to be used for soap-making. The United States laws permit “lethal control” or shooting and egg-oiling for their population control over commercial areas. Their large clutch size has been interpreted as an adaptation to food supply fluctuations. While their population is
seemingly stable for now, this may change in the years to come.

Ornithology

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