Phalacrocorax auritus

Geographic Range

Double-crested cormorants breed across North America, as far north as southern Alaska. They winter in North America as far south as Sinaloa, Mexico, and are common on marine and inland waters throughout their range.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

Double-crested cormorants are found in a variety of marine and inland aquatic habitats. They require water for feeding and nearby perches, such as rocks, sandbars, pilings, shipwrecks, wires, trees or docks for resting on and drying out during the day.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal

Physical Description

Cormorants are large birds (70 to 90 cm in length, 1.2 to 2.5 kg) with dark brown or black plumage that has a dull greenish or bronze sheen. They have lean bodies, long necks and relatively short wings. They have long beaks with a hooked upper mandible and bright orange-yellow skin that covers the face, throat and base of the bill. Their black feet are webbed feet and found on short legs, and their tails are wedge-shaped. During the breeding season, double-crested cormorants have two curly black crests on their heads, blue eyelids, a dusky bill and orange on the throat sac and lores. In the winter, adults lack the crests, show no blue on eyelids, have a yellow bill with red on gular sac, and yellow behind the ocher.

Males are slightly bigger than females. Juveniles are much duller in color than adults. They are usually dark brown with grayish or whitish coloring underneath. (Pearson 1936)

There are five subspecies of double-crested cormorants. These subspecies are differentiated by size and the color and shape of their crests.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• ornamentation ornamentation

Reproduction

Cormorants are monogamous and breed in colonies of up to three thousand pairs. The male chooses a nest site and then advertises for a female by standing in a “wing-waving display” that shows off the brightly-colored skin on his head and neck. Males also perform elaborate courtship dances, including dances in the water where they present the female with nest material. After forming a pair, double-crested cormorants lose their crests.

Double-crested cormorants do not defend a large territory around the nest. They defend a small area immediately around the nest that is less than one meter in diameter.

• Mating System
• monogamous monogamous

Double-crested cormorants breed between April and August, with peak activity occurring in May through July. The males arrive at the breeding colony first and chose a nest site. They then advertise for a mate. The male and female work together to repair an old nest or to build a new one of sticks, twigs, vegetation and flotsam and jetsam found nearby, including rope, fishnet, buoys and deflated balloons. The male brings most of the material to the female who builds the nest and guards it from other colony members who would otherwise steal the nest materials. The nests typically built on the ground, but are occasionally built in trees. After nest construction is complete, the female lays 1 to 7 (usually 4) pale bluish-white eggs with a chalky coating. The eggs are laid 1 to 3 days apart. Both parents incubate the eggs, which hatch asynchronously after 25 to 28 days. The newly hatched young are altricial, and are cared for by both parents. Both parents feed the chicks regurgitated food. The young begin to leave the nest when they are 3 to 4 weeks old. They can fly at about 6 weeks and dive at 6 to 7 weeks. The chicks become completely independent of their parents by 10 weeks of age. Double-crested cormorants do not breed until they are at least 2 years old.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Both parents incubate the eggs and care for the altricial chicks. The parents feed the chicks regurgitated food 2 to 6 times per day. On hot days, parents fetch water and pour it directly from their beak into the open mouths of the chicks.

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

The oldest known wild double-crested cormorant lived to be 17 years and 9 months old. The average life expectancy for wild birds is 6.1 years.

Behavior

Double-crested cormorants are very gregarious. They can be found in small and large groups both on the breeding grounds, and during the winter. They breed in colonies and often feed in large flocks. They also migrate in large groups.

Double-crested cormorants feed during the day by diving for fish. After diving, cormorants look for an elevated spot to perch with their wings outspread. This is most likely done to dry out the feathers. This behavior is not a direct response to water, however, as captive cormorants that do not dive for their food still perch to dry their feathers after eating.

• Key Behaviors
• flies
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• colonial colonial

Communication and Perception

Double-crested cormorants use calls and physical displays to communicate with one another. While cormorants use their small range of calls in certain social situations, they are largely silent. One example of the physical displays used to communicate between cormorants is the "wing wave display" used by males to attract a mate.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Double-crested cormorants feed primarily on fish, but also eat insects, crustaceans and amphibians. They generally feed in shallow water (less than 8 m deep) within 5 km of shore, diving underwater to catch their prey. They may swallow small fish while underwater, but bring larger prey up to the surface to shake, clean or hammer on the water before consuming them.

When feeding on schooling fish, cormorants may feed together in flocks. They have a hook-like tip on the upper maxilla of their bill and specialized muscles that aid them in grasping their slippery prey.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• amphibians
• fish
• insects
• aquatic crustaceans

Predation

Gulls , crows and jays and grackles are probably significant predators of cormorant eggs and chicks. Coyotes , foxes and raccoons may also prey on cormorant chicks. Adult cormorants and chicks are susceptible to predation by bald eagles , and occasionally by great horned owls , caiman and brown pelicans .

When threatened by a predator, gulls may threaten the predator or vomit fish at them. If the predator is large, the adults usually leave the nest, and circle overhead.

Ecosystem Roles

Double-crested cormorants may nest with up to thirteen other species of colony-nesting birds. Within these mixed colonies, they may affect nest-site availability to other species, and provide food for the other species by means of chicks, eggs, pellets, regurgitated fish and stolen food. Cormorants also hunt in mixed flocks, benefiting others and benefiting others through their combined effort to find prey.

Double-crested cormorants impact the populations of the fish they consume.

Economic Importance for Humans: Positive

Double-crested cormorants have no known positive impact on humans.

Economic Importance for Humans: Negative

Double-crested cormorants and other fish-eating birds are considered by some to be detrimental to commercial fisheries and fish farms. However, the extent of their impact on fish populations is difficult to quantify, and has been demonstrated by some studies to be very small. Some landowners also complain of lowering of property values as a result of the impact of double-crested cormorants on vegetation. Finally, double-crested cormorants have been implicated as vectors for fish diseases and parasites.

Conservation Status

Populations of double-crested cormorants have increased dramatically over the last thirty years. This species has no special protection under CITES or the Endangered Species Act. It is, however, protected under the U.S. Migratory Bird Act.

Cormorants are susceptible to poisoning from pesticides and other contaminants, and to oil spills. They are sometimes killed or injured when they are caught on fishhooks and in gill-nets, lobster traps, and trawls. They are also very susceptible to disturbance at their nest sites. Adult cormorants leave the nest unguarded when they are disturbed, leaving the chicks and eggs vulnerable to predation by gulls and other predators, and to overheating in the hot sun.

Other Comments

Phalacrocorax auritus are also referred to as crow ducks, shag, water-turkeys and lawyers. There are several subspecies of Phalacrocorax auritus , including the Florida cormorant ( Phalacrocorax auritus floridanus ), found around Florida, North Carolina, and the Gulf Coast; the white-crested cormorant ( Phalacrocorax auritus cincinatus ), found in Alaska; and the Farallon cormorant ( Phalacrocorax auritus albociliatus ), found on the coasts and inland lakes of the Pacific slope. (Pearson 1936)

Double-crested cormorants account for a large portion of the bird population that winters in the Florida Bay, along with the roseate spoonbills, great white herons , and reddish egrets . (Rodgers 1996)

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Kari Kirschbaum (author, editor), Animal Diversity Web.

Elizabeth Ward (author), Cocoa Beach High School, Penny Mcdonald (editor), Cocoa Beach High School.

References

Brooke, M., T. Birkhead. 1991. The Cambridge Encyclopedia of Ornithology . Cambridge: Cambridge University Press.

Central Flyway Waterfowl Council, 1994. "Waterfowl Identification in the Central Flyway" (On-line). Accessed February 11, 2000 at http://www.npwrc.usgs.gov/resource/tools/waterfwl/waterfwl.htm .

Hatch, J., D. Weseloh. 1999. Double-crested cormorant ( Phalacrocorax auritus ). Pp. 1-36 in The Birds of North America , Vol. 441. Philadelphia, PA: The Birds of North America, Inc.

Landsborough, T. 1964. A New Dictionary of Birds . New York: McGraw-Hill Book Company.

Pearson, T. 1936. Birds of America . New York: Garden City Books.

Perrins, C. 1990. The Illustrated Encyclopedia of Birds . New York: Prentice Hall Press.

Rodgers, J., H. Kale II, H. Smith. 1996. Rare and Endangered Biota of Florida Volume V. Birds . Gainsville, FL: University of Florida.

1972. Grzimek's Animal Life Encyclopedia . New York: Van Nostrand Reinhold Company.

1967. The Larousse Encyclopedia of Animal Life . New York: McGraw-Hill Book Company.