Cormorant
Cormorants, members of the family Phalacrocoracidae, are approximately 40 species of medium- to large aquatic birds renowned for their specialized diving adaptations that enable pursuit of fish prey in underwater environments.[1][2] These foot-propelled divers feature long, flexible necks, sharply hooked bills for grasping slippery quarry, and dense, poorly waterproofed plumage that necessitates post-dive wing-spreading to facilitate drying.[1][3] Widely distributed across temperate and tropical regions on every continent except Antarctica, they occupy diverse habitats including coastal seas, rivers, lakes, and estuaries, often forming large colonies for breeding and foraging.[4][5] Physically robust with body lengths ranging from 45 to 100 centimeters and weights up to 5 kilograms in larger species, cormorants exhibit countershading plumage—dark dorsally and lighter ventrally—for camouflage during dives, alongside reduced buoyancy from solid bones and compact bodies.[6][7] Their foraging dives typically reach depths of 10 to 30 meters, though some records exceed 90 meters, with propulsion achieved via lobed toes on webbed feet rather than wings, which are held folded against the body underwater.[8][9] Ecologically significant as piscivores, cormorants influence fish populations and face human conflicts in aquaculture settings due to their efficient predation, yet their populations remain stable or recovering in many areas owing to adaptable behaviors and broad diets.[10][11]Nomenclature
Etymology and common names
The English word cormorant derives from Middle English cormeraunt, borrowed from Old French cormaran or cormarenc, which in turn stems from Late Latin corvus marinus, literally "sea raven" or "sea crow," alluding to the bird's dark, crow-like appearance and marine foraging behavior.[12][13] This etymological root emphasizes the family's characteristic blackish plumage and diving prowess in coastal or inland waters, distinguishing them from terrestrial corvids.[14] Common names for cormorants vary by species, region, and historical usage, often incorporating descriptors of size, crest, or color; for instance, the widespread Phalacrocorax carbo is termed the great cormorant, black cormorant, or great black cormorant in different locales.[15] Smaller or crested species, such as those formerly grouped under "shags," receive names like European shag (Gulosus aristotelis) or common shag, reflecting interchangeable historical nomenclature that prioritized physical traits over strict taxonomy.[16] In North America, prominent examples include the double-crested cormorant (Nannopterum auritum), also known regionally as crow-duck or white-crested cormorant.[17] These designations persist despite taxonomic revisions separating shags into distinct genera, underscoring the practical, descriptive origins of vernacular terms over Linnaean precision.[18]Taxonomy and phylogeny
Classification and genera
The family Phalacrocoracidae, comprising cormorants and shags, is classified within the order Suliformes, alongside other diving birds such as darters (Anhingidae) and gannets (Sulidae).[1] This placement reflects shared morphological and molecular traits, including adaptations for underwater pursuit diving, though phylogenetic analyses indicate Phalacrocoracidae diverged from other suliforms around 30-40 million years ago.[19] The family encompasses approximately 40 extant species distributed globally in marine, coastal, and freshwater habitats, with no subfamilies universally recognized in modern taxonomy.[1] Historically, most species were lumped under the genus Phalacrocorax, but molecular phylogenetic studies since the late 20th century have supported splitting into multiple genera based on genetic divergence, plumage patterns, and geographic distributions.[20] A key revision by Siegel-Causey (1988) proposed nine genera across two informal groups—shags (with crests or tufts) and cormorants—but subsequent DNA-based analyses refined this to seven primary genera, emphasizing clades like the "microcormorants" and Pacific shags.[20] For instance, Kennedy and Spencer (2014) reallocated species such as the double-crested cormorant (Nannopterum auritum) from Phalacrocorax based on mitochondrial and nuclear markers showing deep divergences exceeding 10 million years.[19] Current genera include:- Microcarbo (5 species, small-bodied "little cormorants" primarily in Asia, Africa, and Australasia, e.g., little cormorant M. niger).[1]
- Poikilocarbo (1 species: red-legged cormorant P. gaimardi, South America).[1]
- Urile (4 species, northern Pacific "cormorants," e.g., pelagic cormorant U. pelagicus; one extinct).[1]
- Phalacrocorax (11 species, restricted to "Old World" cormorants, e.g., great cormorant P. carbo).[1]
- Gulosus (1 species: socotra cormorant G. aristotelis, Arabian Sea).[1]
- Leucocarbo (7 species, Australasian and Antarctic "shags" with white underparts, e.g., black-faced cormorant L. melanoleucos).[1]
- Nannopterum (3 species, New World "cormorants," e.g., double-crested cormorant N. auritum).[1]
Species diversity
The family Phalacrocoracidae encompasses approximately 40 extant species of cormorants and shags, reflecting a moderate level of avian diversity concentrated in coastal and marine environments worldwide.[1] These species are distributed across seven genera, a taxonomic arrangement supported by molecular phylogenetic analyses that resolved longstanding uncertainties in relationships, particularly distinguishing "true" cormorants from shags.[22] The division into genera highlights evolutionary divergences, with higher species richness in southern temperate and polar regions compared to the tropics.[21]| Genus | Number of Species | Distribution and Notes |
|---|---|---|
| Microcarbo | 5 | Small-bodied species in Asia, Africa, and Australasia; includes little cormorant (M. niger). Recent proposals suggest splitting African taxa into a new genus Afrocarbo.[21] |
| Poikilocarbo | 1 | Red-legged cormorant (P. gaimardi), endemic to South American coasts. |
| Urile | 4 | Northern Pacific species, such as Brandt's cormorant (U. penicillatus); adapted to cold waters. |
| Phalacrocorax | 11 | Cosmopolitan "true" cormorants, including great cormorant (P. carbo); widespread in Eurasia, Africa, and parts of the Americas. |
| Gulosus | 1 | Socotra cormorant (G. aristotelis desmarestii), restricted to Arabian Sea islands and vulnerable due to limited range. |
| Nannopterum | 3 | New World species, including double-crested cormorant (N. auritum); found in freshwater and coastal North America. |
| Leucocarbo | 15 | "Blue-eyed shags," with highest diversity in southern oceans; many endemic to sub-Antarctic islands, showing radiation in isolated archipelagos.[23] |