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Circus aeruginosus
Circus aeruginosus, the Western or Eurasian Marsh Harrier, is a large reedbed raptor of Eurasia and Africa, lacking the white rump of the Hen Harrier; extinct in Britain by 1899, it recovered to 590 UK pairs by 2016.
Circus cyaneus
Circus cyaneus, the Hen Harrier, is a Eurasian harrier raptor split in 2016 from the American Northern Harrier (Circus hudsonius) on genetic and morphological grounds; IUCN Least Concern, persecuted in UK uplands.
Circus pygargus
Circus pygargus, Montagu's Harrier (Busard cendré), a migratory ground-nesting raptor breeding from Western Europe to Central Asia and wintering in Africa and southern Asia; IUCN Least Concern with 300,000-550,000 mature individuals but decreasing from agricultural intensification.
Cisticola
Cisticola, genus of small Old World passerine birds in family Cisticolidae, established by Kaup 1829; about 50 grassland species including the polygamous zitting cisticola (Cisticola juncidis), named for basket-like nests.
Cistothorus
Cistothorus (marsh wrens), genus of small American wrens in Troglodytidae erected by Cabanis in 1850; includes Sedge Wren (C. stellaris or C. platensis), Marsh Wren (C. palustris), Grass Wren, and the Endangered Apolinar's Wren.
Clamator
Clamator (Kaup, 1829), chestnut-winged cuckoos, a genus of four non-evictor brood-parasitic cuckoos: great spotted, Jacobin, Levaillant's, and chestnut-winged cuckoos, whose chicks outcompete host nestlings and may lay several eggs per nest.
Clanga
Clanga is a genus of medium-sized eagles in the family Accipitridae known as the spotted eagles, comprising the Greater, Lesser, and Indian Spotted Eagles, formerly placed in Aquila.
Clangula
Clangula (Leach, 1819) is a monotypic sea duck genus of Anatidae holding only the long-tailed duck, Clangula hyemalis, formerly oldsquaw; IUCN Vulnerable, decreasing, 6.2-6.8 million mature individuals.
Coal tit
Coal tit (Periparus ater), a small Eurasian and North African tit of conifer woodland, black cap, white nape patch, about 9 g; famous food hoarder, stable Least Concern population of 90-159 million mature individuals.
Coat of arms of Mexico
Coat of arms of Mexico (Escudo Nacional): golden eagle on a flowering nopal devouring a rattlesnake, from the 1325 Tenochtitlan founding legend; legally fixed design, redesigned 1968 by Francisco Eppens Helguera.
Coccothraustes
Coccothraustes Brisson, 1760, the seed-crusher genus of Fringillidae finches, now monotypic with the Hawfinch Coccothraustes coccothraustes after Evening and Hooded Grosbeaks moved to Hesperiphona in 2025.
Coccyzus
Coccyzus (Spotted-tailed Cuckoos), Vieillot 1816, a New World cuckoo genus including Yellow-billed, Black-billed, Mangrove, and Dark-billed cuckoos; nest-building caterpillar specialists with occasional brood parasitism.
Cochlearius
Cochlearius (boat-billed heron, Kahnschnabelreiher) is a monotypic heron genus from Mexico to Brazil, named for its 7.5 cm scoop bill; nocturnal, Least Concern, subfamily Cochleariinae.
Cockatiel
Cockatiel (Nymphicus hollandicus), also called weero: a small crested Australian cockatoo, sole species of Nymphicinae, native to the arid inland mainland, IUCN Least Concern, and a popular companion bird studied for vocal imitation.
Cockatoo
Cockatoo (family Cacatuidae): about 20 crested, mostly black-or-white Australasian parrots lacking Dyck-texture feathers. Diverged from other parrots ~40.7 Ma; ranges from Least Concern sulphur-crested to critically endangered yellow-crested (under 2,000 mature birds).
Cocos booby
Cocos booby (Sula brewsteri), formerly Brewster's booby, an eastern Pacific sulid seabird split from the brown booby by the AOS in 2024; about 65,000 breeding pairs, expanding westward across the Pacific.
Coelurosauria
Coelurosauria, or coelurosaurs, is a clade of theropod dinosaurs containing tyrannosaurs, raptors, and the birds as its living members; the name means "hollow-tailed lizard", referring to their thin-walled tail bones.
Colibri
Colibri (violetears) is a hummingbird genus, Trochilidae, described by von Spix in 1824; four species from Mexico to Brazil, named for violet ear patches, type species T. serrirostris.
Colius
Colius Brisson, 1760 is a genus of mousebirds (Coliiformes, Coliidae) with four African species: castanotus, colius, leucocephalus, and striatus; folivorous, sunning birds endemic to sub-Saharan Africa.
Collocalia
Collocalia is a genus of small glossy Indo-Pacific swiftlets (family Apodidae) erected by Gray in 1840; once held all swiftlets, now about 11 species after splits from Aerodramus, with salivary nests harvested for bird's nest soup.
Colonia
Colonia is a monotypic genus of tyrant flycatchers (Tyrannidae) holding only the Long-tailed Tyrant, Colonia colonus, a black-and-white Neotropical bird with elongated central tail feathers, ranging from Honduras to Argentina and listed as Least Concern.
Columbidae
Columbidae is the bird family comprising the pigeons and doves, with about 308 species found on every continent except Antarctica, and the extinct dodo and passenger pigeon are members.
Columbiformes
Columbiformes, the order of pigeons and doves (family Columbidae, about 352 species), stocky seed- and fruit-eating birds with crop milk, cosmopolitan except Antarctica, including the extinct dodo and solitaire.
Columbina
Columbina (ground doves) is a genus of small New World doves in Columbidae, subfamily Claravinae, established by von Spix in 1825; includes the Common, Inca, Ruddy, and Blue-eyed ground doves.
Common blackbird
Common blackbird (Turdus merula), also Eurasian blackbird, a thrush native to Europe, northwest Africa and the Middle East; male black with yellow bill, female brown; introduced to Australia and New Zealand; European population about 140 million, Least Concern.
Common buzzard
Common buzzard (Buteo buteo), Western Eurasia's most abundant large raptor: 51-57 cm, 113-128 cm wingspan, soaring and perch-hunting generalist eating rabbits, rodents and birds; UK 63,000 pairs, Least Concern.
Common chiffchaff
Common chiffchaff (Phylloscopus collybita), a small olive-brown European leaf warbler named for its chiff-chaff song; UK population about 1.8 million territories, up 222% since 1967, wintering in southern Europe, North Africa, and the Sahel.
Common crane
Common crane (Grus grus, Eurasian crane), a large Gruidae wetland bird of Europe and Asia; wingspan 220–245 cm; IUCN Least Concern; long-distance migrant wintering in India and Africa; recolonized Britain after 16th-century extinction.
Common cuckoo
Common cuckoo (Cuculus canorus), Eurasian migratory brood-parasitic bird wintering in Africa. Least Concern globally (34.6-54.4 million mature birds) but declining 33% in the UK since 1995, linked to its western migration route through Spain.
Common grackle
Common grackle (Quiscalus quiscula), a large long-tailed icterid blackbird of eastern North America; abundant at ~67 million but down ~54% since 1966, a major corn-crop pest with a federal depredation order.