The true crows are large passerine birds that comprise the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-sized jackdaws (Eurasian and Daurian) to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents (except South America) and several offshore and oceanic islands (including Hawaii).
The crow genus makes up a third of the species in the corvid family. Other corvids include rooks and jays. Crows appear to have evolved in Asia from the corvid stock, which had evolved in Australasia. A group of crows is called a "murder," though this term usually appears in poetry rather than scientific contexts.
There is no good systematic approach to the genus at present. Generally, it is assumed that the species from a geographical area are more closely related to each other than to other lineages, but this is not necessarily correct. For example, while the Carrion/Collared/House Crow complex is certainly closely related to each other, the situation is not at all clear regarding the Australian/Melanesian species. Furthermore, as many species are similar in appearance, determining actual range and characteristics can be very difficult, such as in Australia where the five (possibly six) species are almost identical in appearance.
The fossil record of crows is rather dense in Europe, but the relationships among most prehistoric species is not clear. Jackdaw-, crow- and raven-sized forms seem to have existed since long ago and crows were regularly hunted by humans up to the Iron Age, documenting the evolution of the modern taxa. American crows are not as well-documented.
A surprisingly high number of species have become extinct after human colonization, especially of island groups such as New Zealand, Hawaii and Greenland
Australian and Melanesian species
New Zealand species
Pacific island species
Tropical Asian species
Eurasian and North African species
North and Central American species
Tropical African species
In addition to the prehistoric forms listed above, some extinct chronosubspecies have been described. These are featured under the respective species accounts.
In Auburn NY (USA), 25,000 to 50,000 American Crows (C. brachyrhynchos) have taken to roosting in the small city's large trees during winter since around 1993. In 2003, a controversial, organized crow hunt proved ineffective at reducing their numbers and the problem (concerns for public health and the sheer noise of so many crows) continues.
At a Technology Entertainment Design conference in March 2008, Joshua Klein presented the potential use of a vending machine for crows. He suggested the crows could be trained to pick up trash and the vending machine would be designed to give a reward in exchange for the trash.
In the UK, the crow is considered a pest and under certain conditions can be shot under a number of general licenses issued by DEFRA.
In Australia it is illegal to kill native birds.
The latest evidence appears to point towards an Australasian origin for the early family (Corvidae) though the branch that would produce the modern groups such as jays, magpies and large predominantly black Corvus. Crows had left Australasia and were now developing in Asia. Corvus has since re-entered Australia (relatively recently) and produced five species with one recognized sub-species.
Loud, throaty "caw-aw-ah"'s are usually used to indicate hunger or to mark territory. When defending a nest site or food, crows will usually enlarge their crest feathers and hunch their shoulders to increase their size. Softer, gurgling sounds have also been observed as a sort of beckoning call, or a call of affection. These noises are emitted from within the throat of the bird, much like a cat's purring.
As a group, the crows show remarkable examples of intelligence, and Aesop's fable of The Crow and the Pitcher shows that humans have long viewed the crow as an intelligent animal. Crows and ravens often score very highly on intelligence tests. Certain species top the avian IQ scale. Crows in the northwestern U.S. (a blend of Corvus brachyrhynchos and Corvus caurinus) show modest linguistic capabilities and the ability to relay information over great distances, live in complex, hierarchic societies involving hundreds of individuals with various "occupations", and have an intense rivalry with the area's less socially advanced ravens. Wild hooded crows in Israel have learned to use bread crumbs for bait-fishing. Crows will engage in a kind of mid-air jousting, or air-"chicken" to establish pecking order.
One species, the New Caledonian Crow, has also been intensively studied recently because of its ability to manufacture and use its own tools in the day-to-day search for food, including dropping seeds into a heavy trafficked street and waiting for a car to crush them open. On October 5, 2007, researchers from the University of Oxford, England presented data acquired by mounting tiny video cameras on the tails of New Caledonian Crows. It turned out that they use a larger variety of tools than previously known, plucking, smoothing and bending twigs and grass stems to procure a variety of foodstuffs. Crows in Queensland Australia have learned how to eat the toxic cane toad by flipping the cane toad on its back and violently stabbing the throat where the skin is thinner, allowing the crow to access the non-toxic innards; their long beaks ensure that all of the innards can be removed.
While hawks tend to be the primary daytime predators of crows, their most deadly predators, in many areas, are the owls that hunt by night. Crows also will often mob owls much more fiercely when they find them in daylight than the hawks and other raptors. Frequently crows appear to "play" with hawks, taking turns "counting coup" while escorting the raptor out of their territory. Their attacks on owls, on the other hand, possess a definite serious quality.
The treatment of these rare individuals may vary from group to group, even within the same species. For example, one such individual may receive special treatment, attention, or care from the others in its group, while another group of the same species might exile such individuals, forcing them to fend for themselves. The reason for such behaviors, and why these behaviors vary as they do, is unknown.
Crows, and especially ravens, often feature in European legends or mythology as portents or harbingers of doom or death, because of their dark plumage, unnerving calls, and tendency to eat carrion. They are commonly thought to circle above scenes of death such as battles. The Child ballad The Three Ravens depicts three ravens discussing whether they can eat a dead knight, but finds that his hawk, his hound, and his true love prevent them; in the parody version The Twa Corbies, these guards have already forgotten the dead man, and the ravens can eat their fill. Their depiction of evil has also led to some exaggeration of their appetite. In modern films such as Pirates of the Caribbean: Dead Man's Chest, Damien: Omen II and Exorcist: The Beginning, crows are shown tearing out people's eyes while they are still alive. Crows have never been known for this behavior due to their high preference for carrion.
In the Epic of Gilgamesh, the Chaldean myth, the character Utnapishtim releases a dove and a raven to find land, however, the dove merely circles and returns. Only then does Utnapishtim send forth the raven, who does not return. Utnapishtim extrapolates from this that the raven has found land, which is why it hasn't returned. This would seem to indicate some acknowledgement of crow intelligence, which may have been apparent even in ancient times, and to some might imply that the higher intelligence of crows, when compared to other birds, is striking enough that it was known even then.
In occult circles, distinctions are sometimes made between crows and ravens. In mythology and folklore as a whole, crows tend to be symbolic more of the spiritual aspect of death, or the transition of the spirit into the afterlife, whereas ravens tend more often to be associated with the negative (physical) aspect of death. However, few if any individual mythologies or folklores make such a distinction, and there are ample exceptions. Another reason for this distinction is that while crows are typically highly social animals, ravens don't seem to congregate in large numbers anywhere but:
Amongst Wiccans, crows are often thought to be highly psychic and are associated with the element of ether or spirit, rather than the element of air as with most other birds. This may in part be due to the long-standing occult tradition of associating black with "the abyss" of infinite knowledge (see akasha), or perhaps also to the more modern occult belief that wearing black aids in psychic ability, as it absorbs more electromagnetic energy, since surfaces appear black by absorbing all frequencies in the visible spectrum, reflecting no color.
In Chinese mythology, they believed that the world at one time had 10 suns that were caused by 10 crows. The effect was devastating to the crops and nature, so they sent in their greatest archer Houyi to shoot down 9 crows and spare only one. Also Chinese people believe that crows mean bad luck, probably due to the colour black. Having a "crow beak" is a symbolic expression that one is being a jinx.
A very incomplete list includes the eponymous Pacific Northwest Native figures Raven and Crow, the ravens Hugin and Munin, who accompany the Norse god Odin, the Celtic goddesses the Mórrígan and/or the Badb (sometimes considered separate from Mórrígan), and Shani, a Hindu god who travels astride a crow. In Buddhism, the Dharmapala (protector of the Dharma) Mahakala is represented by a crow in one of his physical/earthly forms. Avalokiteśvara/Chenrezig, who is reincarnated on Earth as the Dalai Lama, is often closely associated with the crow because it is said that when the first Dalai Lama was born, robbers attacked the family home. The parents fled and were unable to get to the infant Lama in time. When they returned the next morning expecting the worst, they found their home untouched, and a pair of crows were caring for the Dalai Lama. It is believed that crows heralded the birth of the First, Seventh, Eighth, Twelfth and Fourteenth Lamas, the latter being the current Dalai Lama, Tenzin Gyatso. Crows are mentioned often in Buddhism, especially Tibetan disciplines. In Greek mythology, it was believed that when the crows gave bad news to the goddess Athena, she flew into a rage, and cursed their feathers to be black. Myths in India: In Hinduism, it is believed that people who died will take food and offerings through a variety of crows called "Bali kākka". Every year people whose parents or relatives died will offer food to crows as well as cows on the Shradha day. A battle between crows and owls is said to have inspired the final bloody night of the Mahabharatha war.