Common Raven
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[Photo] Corvus corax at Bryce Canyon National Park. Source: http://www.nps.gov/brca/images/raven300.jpg

The Common Raven (Corvus corax) is a large black bird in the crow family, with iridescent feathers. The bill is large and slightly curved. At maturity, it is between 56 and 69 cm (22 to 27 inches) in length, with a wingspan double that.

Apart from its greater size, the Raven differs from its cousins the crows by having a larger and heavier beak, and a deeper and more varied barking prrrukk call note. Other field points are the shaggy throat feathers and a longer, wedge-shaped tail.

This raven is prominent in human culture.

Distribution and habitat
Ravens can thrive in varied climates; indeed this species has the largest range of any member of the genus. They range from the Arctic to the deserts of North Africa, and to islands in the Pacific Ocean. In the Faroe Islands a pied colour-morph of this species occurred among all-black birds; known as the Pied Raven, it eventually disappeared in the mid 20th Century, probably due to selective collection for its unusual plumage.

Most Ravens prefer wooded areas (with large, open land nearby) or coastal regions for their nesting sites and feeding grounds. In some areas of large human population, such as California in the United States, Ravens take advantage of an enlarged food supply and have seen a surge in population. In other areas, such as parts of Europe and the eastern United States, Raven populations have been greatly reduced due to persecution.

Behavior
Diet
Adult ravens have a varied diet. They will eat a wide number of foods, including insects, berries, fruit, other birds' eggs, carrion, undigested portions of wolf feces, and human-produced foods such as bread. They also may kill small birds and mammals, including young rabbits and rats, but do so mainly as opportunists.

Nesting
Much Raven behavior is related to mating and reproduction. Juveniles begin to court at a very early age, but may not bond for another 2-3 years. Aerial acrobatics and displays of intelligence and ability to provide food are key behaviors of courting Ravens. Once paired, Ravens tend to nest together for life, usually in the same location. The pair will build a nest on a cliff ledge or a tall tree (or a building ledge in cities).

Breeding pairs must have a territory of their own before they begin nest-building and reproduction, and the territory and its food resources will be defended against others. The nest is made of large sticks and twigs lined with a softer material, such as deer fur. The female will lay from three to seven pale bluish-green, brown-blotched eggs. Both parents keep the eggs warm, and take turns feeding the chicks. As with many birds, pairing does not necessarily mandate sexual monogamy, and raven habits show fluidity in this regard.

Intelligence
Popular beliefs about Ravens include the notion that they are attracted to shiny objects, but research indicates that juveniles are deeply curious about all new things, and that Ravens retain an attraction to bright, round objects based on their similarity to bird eggs. Mature Ravens lose their intense interest in the unusual, and become highly neophobic. Ravens usually live ten to fifteen years in the wild, or twice that in captivity.

Ravens have impressed their biologist observers with their apparent intelligence and insight. Experiments have shown that members of the crow family are capable of using tools; an experiment, where some desirable item lay on the bottom of a bottle, showed that some of these birds were able to form a hook to reach the item. Like other corvids, Ravens can copy sounds from their environment, including human speech. They have a wide range of vocalizations, which remain the object of interest to ornithologists.

Taxonomy
A 2005 molecular study reviewed segments of DNA of the Common Raven and found some issues with the current species classification of it and related species. There appear not only to be two clades, a Holarctic and a Californian, but that the related Chihuahuan Raven (C. cryptoleucus) is a sister group to the Californian clade and the Pied Crow (C. albus) is sister to the Holarctic clade.[2]

A recent study shows Canary Island Ravens (Corvus corax tingitanus) have distinct mtDNA.[3]

Ravens in human culture
There are many references to ravens in legends and literature.

The raven is the national bird of Bhutan because it adorns the royal hat, representing the deity Gonpo Jarodonchen (Mahakala with a raven's head); one of the important guardian deities of Bhutanese culture. The Common Raven is the official bird of the Yukon and of the city of Yellowknife, Northwest Territories.

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