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 those of all cormorants, are not waterproof and it must spend time drying 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. Physically, this subspecies is fairly large and has white to partially white nuptial crests. 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. N. a. cincinnatum (Brandt 1837), white-crested cormorant, 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. Physically, this subspecies is the largest and it bears straight, white nuptial crests. N. a. floridanum (Audubon 1835), Florida cormorant, 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. N. a. heuretum This subspecies bears straight, white nuptial crests. 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.