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 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 René Primevère Lesson in 1831. It was formerly classified in the genus Phalacrocorax, but a 2014 study supported reclassifying it and several other American cormorant species into the genus Nannopterum. The IOC followed this classification in 2021.

Its scientific genus name is derived from the Greek words : nános, "small" and : 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 ', "eared", referring to its nuptial crests. Its common name refers to the same nuptial crests.

Five subspecies are recognized:

  • N. a. albociliatum (Ridgway 1884), Farallon cormorant, 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 Territory, Mexico, and was recorded in 1913.
  • N. a. auritum (Lesson, 1831), 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 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.

Description

thumb|Close-up of an adult in breeding plumage with dark crests

thumb|upright|Adult in breeding plumage with white crests

thumb|right|Juvenile plumage, California

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 long, with a wingspan of between . Double-crested cormorants weigh between . Males and females do not display sexual dimorphism.

Behavior

thumb|right|Displaying, [[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 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. 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 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 suspected of contributing to the decline of some sport-fish populations in the Great Lakes and other areas.

In May 2008, the Canadian government reduced significantly the number of nests of the birds on Middle Island, a small island in Lake Erie and part of Point Pelee National Park. This is an attempt to keep the small island in balance and preserve its vegetation but opponents to the plan have argued that it is based on faulty information, provided in part by anglers who view cormorants as competitors. As of 2021, the cormorant culling program continues.

In 2020 the government of Ontario introduced a hunting season for double-crested cormorants from September 15 to December 31, allowing any hunter to kill up to fifteen birds per day.

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File:Phalacrocorax auritusZZ.jpg|Mounted skeleton of Nannopterum auritum at Smithsonian Museum of Natural History

File:Double-crested Cormorants Nesting.jpg|Nesting, Alaska Maritime National Wildlife Refuge

File:Cormorant, Double-crested LOa.jpg|In flight

File:Double-crested Cormorant, juvenile.jpg|Juvenile

File:Birds Florida (17222960883).jpg|Double-crested cormorant in a confrontation with a brown pelican (Pelicanus occidentalis)

File:Phalacrocorax auritus.jpg|alt=Double-crested cormorant (Phalacrocorax auritus), Ballard (Hiram M. Chittenden) Locks, (Seattle, Washington).|Ballard (Hiram M. Chittenden) Locks, (Seattle, Washington).

File:20240813 double crested cormorant beaver brook open space PD200073 02.jpg|Juvenile in the midst of throat-fluttering

</gallery>

References

Further reading

  • Alsop, Fred J. III; Birds of Texas. Smithsonian Handbooks: DK Publishing, Inc., New York, NY (2002).
  • 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.
  • Double-crested cormorant – Cornell Lab of Ornithology
  • Double-crested cormorant – USGS Patuxent Bird Identification InfoCenter