For the bird of prey referred to as "carrion crow" in the Caribbean, seeTurkey vulture.
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The carrion crow was one of the many species originally described byCarl Linnaeus in his landmark 175810th edition ofSystema Naturae, and it still bears its original name ofCorvus corone.[2] The binomial name is derived from theLatincorvus, "raven",[3] andGreekκορώνηkorōnē, "crow".[4]
Thehooded crow (Corvus cornix), formerly regarded as a subspecies, has been split off as a separate species, and there is some discussion whether theeastern carrion crow (C. c. orientalis) is distinct enough to warrant specific status; the two taxa are well separated, and it has been proposed they could have evolved independently in the wetter, maritime regions at the opposite ends of theEurasian landmass.[5]
Along with the hooded crow, the carrion crow occupies a similar ecological niche in Eurasia to theAmerican crow (Corvus brachyrhynchos) in North America. The two species look very similar to one another, but can be differentiated by size, as the carrion crow is larger and of a stockier build compared to the American crow.
The plumage of the carrion crow is black with a green or purple sheen, much greener than the gloss of therook (Corvus frugilegus). The bill, legs and feet are also black. It can be distinguished from thecommon raven by its size of around 48–52 centimetres (19–20 in) in length as compared to an average of 63 centimetres (25 inches) for ravens, and from thehooded crow by its black plumage. The carrion crow has a wingspan of 84–100 centimetres (33–39 in) and weighs 400–600 grams (14 oz – 1 lb 5 oz).
Juvenile carrion crows can be identified by their brownish plumage and blue eyes, both of which darken to black and brown as the crow grows older.
Distribution and genetic relationship to hooded crows
A map of Europe indicating the distribution of the carrion andhooded crows on either side of a contact zone (white line) separating the two species
The carrion crow (Corvus corone) andhooded crow (Corvus cornix), including the former's slightly larger allied form or raceC. c. orientalis, are two very closely related species;[6] the geographic distributions of both forms of carrion crow across Europe are illustrated in the accompanying diagram. It is believed that this distribution might have resulted from the glaciation cycles during thePleistocene, which caused the parent population to split into isolates which subsequently re-expanded their ranges when the climate warmed causing secondary contact.[7][8]
Poelstra and coworkers sequenced almost the entire genomes of both species in populations at varying distances from the contact zone to find that the two species were genetically identical, both in their DNA and in its expression (in the form ofmRNA), except for thelack of expression of a small portion (<0.28%) of the genome (situated on avian chromosome 18) in the hooded crow, which imparts the lighter plumage colouration on its torso.[7] Thus the two species can viably hybridize, and occasionally do so at the contact zone, but the all-black carrion crows on the one side of the contact zone mate almost exclusively with other all-black carrion crows, while the same occurs among the hooded crows on the other side of the contact zone.
It is therefore clear that it is only the outward appearance of the two species that inhibits hybridization.[7][8] The authors attribute this toassortative mating (rather than to ecological selection), the advantage of which is not clear, and it would lead to the rapid appearance of streams of new lineages, and possibly even species, through mutual attraction between mutants. Unnikrishnan and Akhila propose, instead, thatkoinophilia is a more parsimonious explanation for the resistance to hybridization across the contact zone, despite the absence of physiological, anatomical or genetic barriers to such hybridization.[7] The carrion crow is also found in the mountains and forests of Japan and also in the cities of Japan.[9]
The rook is generally gregarious and the crow largely solitary, but rooks occasionally nest in isolated trees, and crows may feed with rooks; moreover, crows are often sociable in winter roosts. The most distinctive feature is the voice. The rook has a high-pitchedkaaa, but the crow's guttural, slightly vibrant, deeper croakedkraa is distinct from any note of the rook.[10]
The carrion crow is noisy, perching on a vantage point such as a building or the top of a tree and calling three or four times in quick succession, with a slight pause between each series of croaks. During each series of calls, a crow may perform an accompanying gesture, raising its shoulders and bowing its head and neck downwards with each caw. The wing-beats are slower, more deliberate than those of the rook.[11]
Carrion crows can becometame near humans, and can often be found near areas of human activity or habitation including cities, moors, woodland, sea cliffs and farmland[12] where they compete with other social birds such asgulls, other corvids, andducks for food in parks and gardens.
The carrion crow can be seen performing bowing gestures while cawing.
Other vocalizations of the carrion crow include clicking.
Like other species of corvid, carrion crows will actively harass predators and competitors that enter their territory or threaten them or their offspring, and will engage in groupmobbing behaviour as a method to defend themselves.[13]
Like allcorvids, carrion crows are very intelligent.[14] For example, they can discriminate between numerosities up to 30,[15] flexibly switch between rules,[16] and recognise human and crow faces.[17] Given the difference in brain architecture in crows compared to primates, these abilities suggest that their intelligence is realised as a product ofconvergent evolution.[14]
Though an eater ofcarrion of all kinds, the carrion crow will eatinsects,earthworms, otherinvertebrates,[18] grain, fruits, seeds, nuts,[18] smallmammals,amphibians,fish,[18] scraps and will also steal eggs. Crows are scavengers by nature, which is why they tend to frequent sites inhabited byhumans in order to feed on their household waste. Crows will also harassbirds of prey or evenfoxes for their kills. Crows actively hunt and occasionally co-operate with other crows to make kills, and are sometimes seen catchingducklings for food. Due to their gregarious lifestyle and defensive abilities, carrion crows have few natural predators. However, powerful raptors such as theEurasian goshawk,peregrine falcon,Eurasian eagle-owl andgolden eagle will readily hunt them, and crows can become an important prey item locally.
The bulky stick nest is usually placed in a tall tree, but cliff ledges, old buildings and pylons may be used as well. Nests are also occasionally placed on or near the ground. The nest resembles that of thecommon raven, but is less bulky. The 3 to 4 brown-speckled blue or greenish eggs are incubated for 18–20 days by the female alone, who is fed by the male. The young fledge after 29–30 days.[19]
Chicks in the nest
It is not uncommon for an offspring from the previous years to stay around and help rear the new hatchlings. Instead of seeking out a mate, it looks for food and assists the parents in feeding the young.[20]
^Holden, Peter (2012).RSPB Handbook of British Birds. Christopher Helm. p. 274.ISBN978-1-4081-2735-3.
^Pettifor, R. A (1990). "The effects of avian mobbing on a potential predator, the European kestrel, Falco tinnunculus".Animal Behaviour.39 (5):821–827.doi:10.1016/S0003-3472(05)80945-5.S2CID53200478.
^abNieder A.; et al. (2017). "Inside the corvid brain—probing the physiology of cognition in crows".Current Opinion in Behavioral Sciences.16 (8):8–14.doi:10.1016/j.cobeha.2017.02.005.S2CID44291562.
^Baglione, V.; Marcos, J. M.; Canestrari, D.; Ekman, J. (2002). "Direct fitness benefits of group living in a complex cooperative society of carrion crows, Corvus corone corone".Animal Behaviour.64 (6):887–893.doi:10.1006/anbe.2002.2007.S2CID53200940.
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