Crow

Crows are large passerine birds that form 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). In the United States and Canada, the word "crow" is used to refer to the American Crow.

The crow genus makes up a third of the species in the Corvidae family. Other corvids include rooks and jays. Crows appear to have evolved in Asia from the corvid stock, which had evolved in Australia. A group of crows is called a flock or a murder.

Recent research has found some crow species capable not only of tool use, but of tool construction as well. Crows are now considered to be among the world's most intelligent animals. The Jackdaw and (along with its fellow corvid, the European Magpie) has been found to have a neostriatum approximately the same relative size as is found in chimpanzees and humans, and significantly larger than is found in the gibbon.

Evolutionary history and systematics
Crows appear to have evolved in central Asia and radiated out into North America, Africa, Europe, and Australia.

The latest evidence regarding the crow's evolution indicates descent from the Australasian family Corvidae. However, the branch that would produce the modern groups such as jays, magpies and large predominantly black Corvus had left Australasia and were concentrated in Asia by the time the Corvus evolved. Corvus has since re-entered Australia (relatively recently) and produced five species with one recognized sub-species.

The genus was originally described by Linnaeus in his 18th century work Systema Naturae. The name is derived from the Latin corvus meaning "raven".

The type species is the Common Raven (Corvus corax); others named in the same work include the Carrion Crow (C. corone), the Hooded Crow (C. cornix), the Rook (C. frugilegus), and the Jackdaw (C. monedula). The genus was originally broader, as the Magpie was designated C. pica before later being moved into a genus of its own. There are now considered to be at least 42 extant species in this genus, and at least 14 extinct species have been described.

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 are not clear. 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.

A surprisingly high number of species have become extinct after human colonization, especially of island groups such as New Zealand, Hawaii and Greenland.

Calls
Crows make a wide variety of calls or vocalizations. Whether the crows' system of communication constitutes a language is a topic of debate and study. Crows have also been observed to respond to calls of other species; this behavior is presumably learned because it varies regionally. Crows' vocalizations are complex and poorly understood. Some of the many vocalizations that crows make are a "Koww", usually echoed back and forth between birds, a series of "Kowws" in discrete units, counting out numbers, a long caw followed by a series of short caws (usually made when a bird takes off from a perch), an echo-like "eh-aw" sound, and more. These vocalizations vary by species, and within each species vary regionally. In many species, the pattern and number of the numerical vocalizations have been observed to change in response to events in the surroundings (i.e. arrival or departure of crows). Crows can hear sound frequencies lower than those that humans can hear, which complicates the study of their vocalizations.

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.

Intelligence
As a group, 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 bird. Crows and ravens often score very highly on intelligence tests. Certain species top the avian IQ scale. 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. Crows have been found to engage in feats such as tool use, the ability to hide and store food across seasons, episodic-like memory, and the ability to use individual experience in predicting the behavior of environmental conspecifics.

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. These tools include 'knives' cut from stiff leaves and stiff stalks of grass. Another skill involves dropping tough nuts into a 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.

Recent research suggests that crows have the ability to recognize one individual human from another by facial features.

Disease
The American crow is very susceptible to the recently introduced North American strain of West Nile virus. American crows usually die within one week of acquiring the disease with only very few surviving exposure. Crows are so affected by the disease that their deaths are now serving as an indicator of the West Nile Virus’ activity in an area.

Conservation status
Two species of crow have been listed as endangered by the US fish and wildlife services: The ʻAlalā and the Mariana Crow. The American Crow, despite having its population reduced by 45% since 1999 by the West Nile Virus, is considered a Species of Least Concern.

In human culture
The Common Raven, Australian Raven and Carrion Crow have been blamed for killing weak lambs and are often seen eating freshly dead corpses probably killed by other means. Rooks have been blamed for eating grain in the UK and Brown-necked Raven for raiding date crops in desert countries.

In Auburn, New York (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.

Crows have also been known to imitate the human voice, just like parrots. Crows that have been trained to "speak" are considered valuable in parts of East Asia, as crows are a sign of luck.

Some people have adopted crows as pets.

Though humans cannot generally tell individual crows apart, crows have been shown to have the ability to visually recognize individual humans, and to transmit information about "bad" humans by squawking.

Myth and spirituality


In Irish mythology, crows are associated with Morrigan, the goddess of war and death.

In Norse mythology, Huginn and Muninn are a pair of ravens that fly all over the world, Midgard, and bring the god Odin information.

In Australian Aboriginal mythology, Crow is a trickster, culture hero and ancestral being. Legends relating to Crow have been observed in various Aboriginal language groups and cultures across Australia; these commonly include stories relating to Crow's role in the theft of fire, the origin of death and the killing of Eagle's son.

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.

According to Ovid's Metamorphoses, in classical Greek mythology, when the crow told the god Apollo that his lover Coronis was cheating on him with a mortal, he became very angry, and part of that anger was directed at the crow, whose feathers he turned from white to black.

In the Story of Bhusunda, a chapter of the Yoga Vasistha, a very old sage in the form of a crow, Bhusunda, recalls a succession of epochs in the earth's history, as described in Hindu cosmology. He survived several destructions, living on a wish-fulfilling tree on Mount Meru.

Crows are mentioned often in Buddhism, especially Tibetan disciplines. 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.

In Japanese mythology, a three-legged crow called Yatagarasu (八咫烏) is depicted. In Korean mythology, there is a three-legged crow known as Samjokgo (hangul: 삼족오; hanja: 三足烏). During the period of the Goguryeo Kingdom, the Samjogo was a highly regarded symbol of power, thought superior to both the dragon and the Korean phoenix.

In Chinese mythology, the world originally had ten suns embodied as ten crows, which rose in the sky one at a time. When all ten decided to rise at once, the effect was devastating to crops, so the gods sent their greatest archer Houyi, who shot down nine crows and spared only one. Having a "crow beak" is a symbolic expression that one is being a jinx.

Compendium of Materia Medica states that crows are kind birds that feed their old and weakened parents; this is often cited as a fine example of filial piety.

Ancient Greek authors tell how a jackdaw, being a social creature, may be caught with a dish of oil which it falls into while looking at its own reflection. The Roman poet Ovid saw them as a harbinger of rain (Amores 2,6, 34). In Greek legend, a princess Arne was bribed with gold by King Minos of Crete, and was punished for her avarice by being transformed into an equally avaricious jackdaw, who still seeks shiny things. In Aesop's Fables, the jackdaw embodies stupidity in one tale, by starving while waiting for figs on a fig tree to ripen, and vanity in another - the daw sought to become king of the birds with borrowed feathers, but was shamed when they fell off. Pliny notes how the Thessalians, Illyrians and Lemnians cherished jackdaws for destroying grasshoppers' eggs. The Veneti are fabled to have bribed the jackdaws to spare their crops. Another ancient Greek and Roman adage runs, "The swans will sing when the jackdaws are silent," meaning that educated or wise people will speak after the foolish become quiet. In reality, the family of corvidae is among the most intelligent birds in the world, and this association with the ignorant is rather inaccurate.