Double-crested cormorant

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Double-crested Cormorant
Adult in non-breeding plumage.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Pelecaniformes
Family:
Phalacrocoracidae
Genus:
Phalacrocorax
Species:
P. auritus
Binomial name
Phalacrocorax auritus
Synonyms

Carbo auritus Lesson, 1831
Dilophalieus auritus (Lesson, 1831)
Phalacrocorax dilophus

The Double-crested Cormorant (Phalacrocorax auritus) is a member of the cormorant family of seabirds. It occurs along inland waterways as well as in coastal areas and is widely distributed across North America. Five subspecies are recognized. Once threatened by use of DDT, the numbers of this bird have increased markedly in recent years.

Taxonomy

The Double-crested Cormorant was described by Rene Primevere Lesson in 1831. Its scientific name is derived from the Greek words φαλακρος (phalakros), 'bald' and κοραξ (korax), 'crow' or 'raven,' and the Latin auritus, 'eared,' referring to its nuptial crests. Its common name refers to the same nuptial crests. Other common names of this species include Crow-duck, Lawyer, Nigger Goose, Shag and Taunton Turkey (in New England).[2]

Five subspecies are recognized:[3]

  • P. a. albociliatus (Ridgway 1884[4]), Farallon Cormorant[5], breeds along the Pacific coast of North America from British Columbia to Bird Island in the state of Sinaloa, Mexico and possibly even further south. Significant colonies of these birds may also be found further inland including areas around the Salton Sea. According to currently available information, this subspecies is the third largest among the subspecies of the Double-crested Cormorant. Historical records indicate that this species was far more abundant in the past, but due to human persecution and development in their breeding range, the population of this subspecies has declined. The largest colony of cormorants in North America consisted of members of this subspecies at San Martin Island, Baja California, Mexico, and was recorded in 1913.[6] Physically, this subspecies is fairly large and has white to partially white nuptial crests.[7]
  • P. a. auritus (Lesson, 1831), this, the nominate subspecies, has the largest and most widespread breeding population. It ranges from the Great Basin and Rocky Mountains east into central and eastern North America. This region includes the Canadian prairies and the Great Lakes. Historically, this subspecies has bred in abundance across most of this region, though there are questions as to if this bird has always bred in the Great Lakes region. Some evidence indicates that the bird has only begun breeding in the region since the eary 20th century while other evidence suggests that it has been bredding in the region much longer. Physically, this subspecies is moderately large and has black nuptial crests.[8][9]
  • P. a. cincinatus (Brandt 1837[10]), White-crested Cormorant[11], currently, this is the most restricted subspecies, geographically, and it has the smallest population of Double-crested Cormorant subspecies. It is found along the southern coast of Alaska and on the Aleutian Islands, ranging west from Kodiak to Chuginidak in the Aleutians. Historically, the range extended west to the Near Islands, but possibly due to nest predation by introduced foxes, the birds were no longer breeding in the area by the mid-1930s.[12] Physically, this subspecies is the largest and it bears straight, white nuptial crests.[13]
  • P. a. floridanus (Audubon 1835[14]), Florida Cormorant[15], the smallest of the five subspecies, it is found from southern and central Texas east to the Atlantic and from North Carolina south to Florida. Records indicate that this subspecies was abundant throughout its range before the 20th century, but now is only abundant in Florida. This bird has dark nuptial crests.[16] Physically, this subspecies is the largest and it bears straight, white nuptial crests.[17]
  • P. a. heuretus

Description

An adult Double-crested Cormorant in breeding plumage with white crests.

The Double-crested Cormorant is a large waterbird with a stocky body,long neck, medium-sized tail, webbed feet and a medium sized hooked bill. It has a body length of between 70–90 cm (28–35 in) long, with a wingspan of between 114–132  cm (45–52 in).[18][19] Double-crested Cormorants weigh between 1200–2500 g (42.36–88.25 ounces) Males and females do not display sexual dimorphism.[20]

This species has dark-colored plumage with bare super-loral skin and gular skin that is yellow or orange. An adult in breeding plumage will be mostly black with the back and coverts being a dark grayish towards the center. Nuptial crests, for which the species is named, are either white, black or a mix of the two. These are located just above the eyes with the bare skin on the face of a breeding adult being orange. A non-breeding adult will lack the crests and have more yellowish skin around the face. The bill of the adult is dark-colored.[21]

The plumage of juvenile Double-crested Cormorants is more dark grey or brownish. The underparts of a juvenile are lighter than the back with a pale throat and breast that darkens towards the belly. As a bird ages, it's plumage will grow darker. The bill of a juvenile will be mostly orange or yellowish.[22]

Distribution and habitat

A very common and widespread species, it winters anywhere that is ice-free along both coasts, as far north as southern Alaska (on the west coast) and southern New England (on the east coast). It can be found as far south as Mexico and the Bahamas. It migrates from the coldest parts of its breeding range, such as eastern Canada, and has occurred in Europe as a very rare vagrant, for example in Great Britain, Ireland and the Azores.

Behavior

Double-crested Cormorants displays, California

The Double-crested Cormorant swims low in the water, often with just its neck and head visible, and dives from the surface. It uses its feet for propulsion and is able to dive to a depth of 1.5–7.5 m (5–25 feet) for 30–70 seconds. After diving, it spends long periods standing with its wings outstretched to allow them to dry, since they are not fully waterproofed. This species flies low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single-file lines.

Diet

Two Double-crested Cormorant and one fish

Food can be found in the sea, freshwater lakes, and rivers. Like all cormorants, the double-crested dives to find its prey. It mainly eats fish, but will sometimes also eat amphibians and crustaceans. Fish are caught by diving under water. Smaller fish may be eaten while the bird is still beneath the surface but bigger prey is often brough to the surface before it is eaten.

Cormorants regurgitate pellets containing undigested parts of their meals such as bones. These pellets can be dissected by biologists in order to discover what they ate.

Breeding

Double-crested Cormorants (Parent and a chick)at the nest

Breeding occurs in coastal areas as well as near inland rivers and lakes. They build stick nests in trees, on cliff edges, or on the ground on suitable islands. They are gregarious birds usually found in colonies, often with other aquatic birds, and have a deep, guttural grunt call.

Double-crested Cormorant call
Two calls of the Double-crested Cormorant
Problems playing this file? See media help.

Recovery

The double-crested cormorant's numbers decreased in the 1960s due to the effects of DDT. Colonies have also been persecuted from time to time in areas where they are thought to compete with human fishing.

Recently the population of Double-crested Cormorants has increased. Some believe that the recovery was allowed by the decrease of contaminants, particularly the discontinued use of DDT. The population may have also increased because of aquaculture ponds in its southern wintering grounds. The ponds favor good over-winter survival and growth.

In 1894, Thomas McIlwraith in his book, Birds of Ontario, concludes his section on Double-crested Cormorants by saying: “When the young are sufficiently grown, they gather into immense flocks in unfrequented sections, and remain until the ice-lid has closed over their food supply, when they go away, not to return till the cover is lifted up in the spring.” Linda Wires and Francesca J. Cuthbert state that there is solid indication that cormorants were once at least as common in North America as they are now, and most likely much more so, but were killed off physically, like so many other predatory and game species, in the 19th century, although beginning earlier than that, and continuing to the present.

For populations nesting in the Great Lakes region, it is believed that the colonization of the lakes by the non-native alewife (a small prey fish) has provided optimal feeding conditions and hence good breeding success. Double-crested cormorants eat other species of fish besides alewives and have been implicated in the decline of some sport-fish populations in the Great Lakes and other areas. Scientists are not in agreement about the exact extent of the role of cormorants in these declines, but some believe that Double-crested Cormorants may be a factor for some populations and in some locations.

In light of this belief, and because of calls for action by the public, the United States Fish and Wildlife Service (the U.S. Federal government agency charged with their protection) has recently extended control options to some other government entities. This includes lethal culling of populations and measures to thwart reproduction, in an effort to control their growing numbers.

The U.S. Fish and Wildlife Service retains oversight, and the control measures are not extended to the general public (no hunting season). Many government agencies at different levels in both the U.S. and Canada continue to wrestle with how best to respond to the situation.

The Canadian government has scheduled a mass culling of the birds on Middle Island, a small island in Lake Erie and part of Point Pelee National Park, to begin as early as April 2008. It is supposed to be an attempt to keep the small island in balance and preserve it’s vegetation, but opponents to he plan have pointed out that it is based on faulty information, provided in part by anglers who view cormorants as competitors. A website has been set up to provide information on the birds and plan as well as to prompt visitors to provide feedback and compel the the Minister of Environment to put a stop to the planned slaughter.[23]

References

  1. ^ BirdLife International (2004), Phalacrocorax auritus: 2007 IUCN Red List of Threatened Species, retrieved 2008-06-11 {{citation}}: Check date values in: |accessdate= (help)
  2. ^ Terres, John K. (1987), The Audubon Encyclopedia of North American Birds, New York: Alfred A. Knopf, p. 106, ISBN 0394466519
  3. ^ Wires, Linda R.; Cuthbert, Francesca J. (March), "Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century", Waterbirds, 29 (1): 9–37 {{citation}}: Check date values in: |date= and |year= / |date= mismatch (help)
  4. ^ ZipcodeZoo.com. "ZipcodeZoo: Phalacrocorax auritus albociliatus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  5. ^ University of Michigan Museum of Zoology. "Animal Diversity Web: Phalacrocorax auritus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  6. ^ Wires, Linda R.; Cuthbert, Francesca J. (March), "Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century", Waterbirds, 29 (1): 9–37 {{citation}}: Check date values in: |date= and |year= / |date= mismatch (help)
  7. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  8. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  9. ^ Wires, Linda R.; Cuthbert, Francesca J. (March), "Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century", Waterbirds, 29 (1): 9–37 {{citation}}: Check date values in: |date= and |year= / |date= mismatch (help)
  10. ^ ZipcodeZoo.com. "ZipcodeZoo: Phalacrocorax auritus cincinatus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  11. ^ University of Michigan Museum of Zoology. "Animal Diversity Web: Phalacrocorax auritus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  12. ^ Wires, Linda R.; Cuthbert, Francesca J. (March), "Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century", Waterbirds, 29 (1): 9–37 {{citation}}: Check date values in: |date= and |year= / |date= mismatch (help)
  13. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  14. ^ ZipcodeZoo.com. "ZipcodeZoo: Phalacrocorax auritus floridanus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  15. ^ University of Michigan Museum of Zoology. "Animal Diversity Web: Phalacrocorax auritus". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  16. ^ Wires, Linda R.; Cuthbert, Francesca J. (March), "Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century", Waterbirds, 29 (1): 9–37 {{citation}}: Check date values in: |date= and |year= / |date= mismatch (help)
  17. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  18. ^ Cornell Laboratories of Ornithology. "All About Birds: Double-crested Cormorant". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  19. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  20. ^ Cornell Laboratories of Ornithology. "All About Birds: Double-crested Cormorant". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
  21. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  22. ^ Alderfer, Jonathan, Ed. (2008), National Geographic Complete Birds of North America, Washington, D.C.: National Geographic, p. 105, ISBN 0792241754{{citation}}: CS1 maint: multiple names: authors list (link)
  23. ^ CDI. "Cormorant Defenders International". {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
Wikimedia Commons has media related to Phalacrocorax auritus.
  • Template:IUCN2006 Database entry includes justification for why this species is of least concern
  • Alsop, Fred J. III; Birds of Texas. Smithsonian Handbooks: DK Publishing, Inc., New York, NY (2002).
  • "Phalacrocorax auritus". Integrated Taxonomic Information System. 9 February. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  • US Fish & Wildlife Service
  • McIlwraith,Thomas; The Birds of Ontario: Being a Concise Account of Every Species of Bird Known to Have Been Found. W. Briggs, Toronto, ON (1894)
  • Wires, Linda A., and Francesca J. Cuthbert; Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century Waterbirds 29(1): 9-37, 2006.

External links

  • Mounted skeleton of Phalacrocorax auritus at Smithsonian Museum of Natural History.
    Mounted skeleton of Phalacrocorax auritus at Smithsonian Museum of Natural History.
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