Double-crested cormorant
Double-crested cormorant Temporal range:
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Adult in non-breeding plumage | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Suliformes |
Family: | Phalacrocoracidae |
Genus: | Nannopterum |
Species: | N. auritum
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Binomial name | |
Nannopterum auritum (
Lesson , 1831) | |
English: Geographical distribution of Double-crested cormorant.
Breeding Migration Year-round Nonbreeding | |
Synonyms | |
Carbo auritus Lesson, 1831 |
The double-crested cormorant (Nannopterum auritum) 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.
Taxonomy
The double-crested cormorant was described by
Its scientific genus name is derived from the Greek words νᾶνος : nános, "small" and πτερόν : pterón, "wing". This genus name was originally coined for the flightless cormorant (N. harrisi), which does have very small wings; although the double-crested cormorant has normal-sized wings, it (along with the neotropic cormorant, N. brasilianum) was still reclassified into the genus Nannopterum when the relationship between it and the flightless cormorant became apparent. The species name is from the Latin auritus, "eared", referring to its nuptial crests.[5] Its common name refers to the same nuptial crests.
Five subspecies are recognized:[6]
- N. a. albociliatum (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 Territory, Mexico, and was recorded in 1913.[6] Physically, this subspecies is fairly large and has white to partially white nuptial crests.[8]
- N. a. auritum (Lesson, 1831), the nominate subspecies, has the largest and most widespread breeding population. It ranges from 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 whether 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 early 20th century while other evidence suggests that it has been breeding in the region much longer. Physically, this subspecies is moderately large and has black nuptial crests.[6][8]
- N. a. cincinnatum (Brandt 1837), white-crested cormorant,[7] currently this is the most geographically restricted subspecies with the smallest population. 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.[6] Physically, this subspecies is the largest and it bears straight, white nuptial crests.[8]
- N. a. floridanum (Audubon 1835), Florida cormorant,[7] 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.[6]
- N. a. heuretum This subspecies bears straight, white nuptial crests.[8] Physically, it is the smallest. It has bare lores and a greenish gloss on the head and neck. It breeds only in the mangroves surrounding interior lakes of San Salvador in the Bahamas. It may also be resident on other Bahamian islands.[9]
Description
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 and 90 cm (28 and 35 in) long, with a wingspan of between 114 and 123 cm (45 and 48 in).[8][10] Double-crested cormorants weigh between 1.2 and 2.5 kg (2.6 and 5.5 lb). Males and females do not display sexual dimorphism.[10]
This species has dark-colored plumage with bare supra-loreal skin and
The plumage of juvenile double-crested cormorants is more dark gray 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, its plumage will grow darker. The bill of a juvenile will be mostly orange or yellowish.[8]
Distribution and habitat
A very common and widespread species, it winters anywhere that is ice-free along both coasts, as far north as southern
.It is resident on
Behavior
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 (4 ft 11 in – 24 ft 7 in) 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
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, crustaceans and insects.[7] 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 brought to the surface before it is eaten. Double-crested cormorants are also considered pests to aquaculturists because of their intense predation on fish ponds which can cause thousands of dollars in losses to farmers. Cormorants regurgitate pellets containing undigested parts of their meals such as bones. These pellets can be dissected by biologists in order to discover what the birds ate.
Breeding
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.
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 studies have concluded that the recovery was allowed by the decrease of contaminants, particularly the discontinued use of DDT.[12] 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."
For populations nesting in the
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 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).[14]
In May 2008, the Canadian government reduced significantly the number of nests of the birds on
Gallery
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Mounted skeleton of Nannopterum auritum at Smithsonian Museum of Natural History
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In flight
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Juvenile
References
- ^ BirdLife International (2012). "Phalacrocorax auritus". IUCN Red List of Threatened Species. 2012. Retrieved 26 November 2013.
- ^ "Nannopterum auritum". NatureServe Explorer. Retrieved 17 April 2024.
- PMID 24994028.
- ^ "Taxonomic Updates – IOC World Bird List". Retrieved 28 July 2021.
- ISBN 978-1-4081-2501-4.
- ^ S2CID 86270584.
- ^ a b c d "Phalacrocorax auritus". Animal Diversity Web.
- ^ ISBN 978-0-7922-4175-1.
- ^ A new subspecies of the double-crested cormorant, Phalacrocorax auritus, from San Salvador, Bahama Islands, George E. Watson, Storrs L. Olson, and J. Robert Miller; Proceedings of the Biological Society of Washington, Vol. 104, pp. 356-369.
- ^ a b c Cornell Laboratories of Ornithology. "All About Birds: Double-crested Cormorant". Retrieved 29 February 2020.
- ^ "Double-crested Cormorant (Nannopterum auritus) - BirdLife species factsheet". datazone.birdlife.org. Retrieved 28 July 2021.
- Environment Canada. Archived from the originalon 6 July 2011.
- US Fish & Wildlife Service. Archived from the original(PDF) on 8 May 2021. Retrieved 28 February 2023.
- ^ "Special double-crested cormorant permit". ecfr.gov. National Archives: Code of Federal Regulations. 12 February 2021. Retrieved 21 October 2021.
- ^ "Earthroots". Earthroots. Archived from the original on 11 October 2008. Retrieved 17 March 2013.
- S2CID 86023367.
- ^ Mackey, Barry Kent (18 August 2016). "Parks Canada mismanaging Middle Island?". Windsor Star. Retrieved 21 July 2017.
- ^ Aziz, Tahmina (26 April 2021). "Cormorant cull to begin at Point Pelee this week, but animal rights group says it's unnecessary". CBC. Retrieved 28 February 2023.
Further reading
- Alsop, Fred J. III; Birds of Texas. Smithsonian Handbooks: DK Publishing, Inc., New York, NY (2002).
- "Phalacrocorax auritus". Integrated Taxonomic Information System. Retrieved 9 February 2006.
- US Fish & Wildlife Service Archived 16 July 2005 at the Wayback Machine
- 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
- Double-crested cormorant – Cornell Lab of Ornithology
- Double-crested cormorant – USGS Patuxent Bird Identification InfoCenter
- Explore Species: Double-crested Cormorant at eBird (Cornell Lab of Ornithology)
- Double-crested cormorant photo gallery at VIREO (Drexel University)
- Interactive range map of Phalacrocorax auritus at IUCN Red List maps