Double-crested cormorant (Phalacrocorax auritus)

Description

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Double-crested cormorant fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Double-crested cormorant description

Not only is this species the most numerous cormorant in North America, it is also the only cormorant in the region that occupies inland as well as coastal areas ^{(3) (4)}. The most distinctive feature of the double-crested cormorant is the bright orange patch of bare skin at the base of the bill, which sits in stark contrast to the glossy black plumage, tinged with green on the upperparts and grey on the wings ^{(2) (3) (5) (6)}. The eyes are bright green, with blue and white spotted eyelids, and during the breeding season, a tuft of black hairs stands prominently on each side of the head, a feature that gives rise to its common name ^{(5) (6)}. The sexes are alike, but the juvenile is somewhat duller with predominantly light brown plumage ^{(2) (3)}. Like other cormorants, the double-crested cormorant displays a number of adaptations for underwater hunting. Its bones are proportionately heavier than other seabirds which, along with a lack of body fat, reduces the bird’s buoyancy on water. The black bill has completely sealed nostrils, meaning it must breath through its mouth at the surface, but can dive unhindered, while the feet are fully webbed and powerfully thrusts of the set-back legs efficiently propel the streamlined body through the water in pursuit of its prey. At sea, the double-crested cormorant is most commonly seen resting at the water’s surface with little more than the small head set on the long, sinuous neck showing ⁽³⁾.     

Size

Length: 76 – 91 cm ⁽²⁾

Wingspan: c. 137 cm ⁽²⁾

Weight

1.7 – 2.1 kg ⁽²⁾

Double-crested cormorant biology

The double-crested cormorant typically forages in shallow waters, usually less than 30 kilometres from the coast, either alone or in large feeding flocks ⁽⁵⁾. After a little dive clear of the water’s surface, its outer feathers quickly become soaked, reducing buoyancy, but the inner feathers are waterproofed and insulate against the cold waters. Like other cormorants, this sleek, efficient predator skilfully catches its prey in its long, hooked beak after an underwater pursuit, whereby alternate strokes of the webbed feet propel and steer the streamlined body forwards ^{(2) (8)}. Each dive rarely lasts longer than 30 seconds between rest intervals of around 20 seconds at the surface, and upon returning to land, the double-crested cormorant assumes a characteristic posture and stands upright with the wings extended outwards, exposing itself to the sun to dry ^{(5) (8)}. This cormorant feeds almost exclusively on fish, such as sandeels, flatfish and perch, although some crustaceans may also be eaten ^{(2) (3)}. 

During the breeding season, this sociable bird gathers into huge colonies of several thousands, often with other cormorants, gulls, auks, herons and ducks ⁽²⁾. Males arrive at nesting sites first, and immediately begin unusual displays to attract a mate, waving their wings while the tail is cocked upward and forward. Upon pairing up, mating birds set about constructing a flimsy nest of sticks and seaweed on the ground, in a tree or even on a pylon ^{(2) (3)}. Breeding pairs regularly change nesting sites between seasons, but competition for the best location is always fierce and breeding birds will engage in aggressive territorial behaviour ^{(3) (5)}. Typically this rarely goes beyond threatening postures, but on occasions when it does, fighting may ensue, with bill-grappling, or birds seizing the opponent by the neck and wings ^{(3) (5) (8)}.  Both the male and female take turns in incubating the clutch of usually 3 or 4 eggs for around 25 to 29 days ^{(2) (3) (5)}. The chicks hatch naked and helpless, and parental care even extends to sheltering the newly hatched young from the sun, with adults observed standing with their wings outstretched with their backs to the sun ^{(3) (5)}. The chicks grow quickly on an energy-rich fish diet and will fledge after around 42 days in the nest, before becoming fully independent after a further 30 days ^{(2) (3)}. The double-breasted cormorant may first breed in its third year and live to over 15 years of age ⁽³⁾.

Double-crested cormorant range

The double-crested cormorant is widely distributed in North America, ranging from Alaska to northwest Mexico on the Pacific coast, and Newfoundland to Florida, Cuba, the Cayman Islands and Turks and Caicos on the Atlantic coast and Caribbean, as well as parts of central Canada and the United States ^{(3) (7)}. Those birds that breed at northern latitudes in the interior of the continent and Atlantic coast migrate southwards before the onset of winter, with many birds spending the cooler months around the Gulf of Mexico, while populations on the Pacific coast may remain at the same location year-round ⁽³⁾.

Double-crested cormorant habitat

The double-crested cormorant occupies a number of sheltered marine habitats, such as estuaries, mangroves, rocky coasts and islands, as well as a diversity of inland freshwater habitats, including ponds, lakes and rivers ^{(2) (4) (7)}. It requires areas to roost at night and rest during the day and is commonly seen perched on exposed rocks, sandbars and trees near favoured fishing sites ⁽³⁾. 

Double-crested cormorant status

Classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾.

Double-crested cormorant threats

Once considered a competitor for fish by both commercial and recreational fisherman, the double-crested cormorant was widely persecuted, with nests and eggs destroyed and adult birds shot ^{(2) (3)}. This was most serious during the 19^thand early 20^thcenturies and led to a significant population decline ^{(3) (4)}. With some respite from this hunting, the population began to recover from the 1920s onwards until the prevalence of pesticides in the environment, such as DDT, reached critical levels in the 1950s, hindering the species’ recovery ⁽²⁾. However, changes in the use of pesticides has allowed the population to once again recover, with numbers increasing dramatically in some areas, such as at the Great Lakes, where the population rose from a few hundred nests in 1960s to over 13,000 in 1987 ⁽²⁾. 

Today, following a remarkable recovery, the double-crested cormorant population possibly numbers over one million birds. Legislation has been submitted to control its numbers as it has been suggested that the rapid increase in this species has caused fish stocks to decline, although the evidence supporting this claim is, at present, sparse ⁽⁴⁾. However, the species has not recovered across its entire range, and at Baja California a large colony was abandoned due to disturbance ^{(2) (3)}. In some areas, the species is threatened by entanglement in fishing gear and disturbance of its nests ⁽³⁾. 

Double-crested cormorant conservation

With the increasingly widespread view that the double-crested cormorant is becoming a pest species, it could face renewed hunting. Measures have already been implemented to control its numbers in New England and on the west coast, where adult birds have been shot. Non-lethal methods for excluding cormorants from fish farms have also been developed, including frightening devices and aerial barriers. However, until these measures are applied consistently, it is likely that the double-crested cormorant will continue to increase in number and range ⁽³⁾.

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

Find out more

To find out more about the conservation of birds in North America, see:

• The American Bird Conservancy:
  http://www.abcbirds.org/

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org

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arkive@wildscreen.org.uk

Glossary

Crustaceans

Diverse group of animals with jointed limbs and a hard chitinous exoskeleton characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters and barnacles.

Incubate

To keep eggs warm so that development is possible.

Territorial

Describes an animal, a pair of animals or a colony that occupies and defends an area.

References

1. IUCN Red List (June, 2010)
   http://www.iucnredlist.org/
2. del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
3. Hatch, J.J. and Weseloh, D.V. (1999) Double-crested cormorant (Phalacrocorax auritus). Cornell Lab of Ornithology. Birds of North America Online.
4. The Cornell Lab of Ornithology (June, 2010)
   http://www.allaboutbirds.org/guide/Double-crested_Cormorant/id
5. Nelson, J.B. (2005) Pelicans, Cormorants, and their Relatives. The Pelecaniformes. Oxford University Press, Oxford.
6. Bond, J. (1993) Birds of the West Indies. Houghton Mifflin Harcourt, Boston, Massachusetts.
7. BirdLife International (June, 2010)
   http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3675&m=0
8. Perrins, C. (2009) The Encyclopedia of Birds. Oxford University Press, Oxford.