The common raven (Corvus corax), also known as the western raven or northern raven when discussing the raven at the subspecies level, is a large all-black passerine bird. Found across the Northern Hemisphere, it is the most widely distributed of all corvids. There are at least eight subspecies with little variation in appearance, although recent research has demonstrated significant genetic differences among populations from various regions. It is one of the two largest corvids, alongside the thick-billed raven, and is possibly the heaviest passerine bird; at maturity, the common raven averages 63 centimetres (25 inches) in length and 1.2 kilograms (2.6 pounds) in mass. Although their typical lifespan is considerably shorter, common ravens can live more than 23 years in the wild, which among passerines only is surpassed by a few Australian species such as the satin bowerbird and probably the lyrebirds. Young birds may travel in flocks but later mate for life, with each mated pair defending a territory.
Common ravens have coexisted with humans for thousands of years and in some areas have been so numerous that people have regarded them as pests. Part of their success as a species is due to their omnivorous diet: they are extremely versatile and opportunistic in finding sources of nutrition, feeding on carrion, insects, cereal grains, berries, fruit, small animals, nesting birds, and food waste.
Some notable feats of problem-solving provide evidence that the common raven is unusually intelligent. Over the centuries, it has been the subject of mythology, folklore, art, and literature. In many cultures, including the indigenous cultures of Scandinavia, ancient Ireland and Wales, Bhutan, the northwest coast of North America, and Siberia and northeast Asia, the common raven has been revered as a spiritual figure or godlike creature.
Description & appearanceA mature common raven ranges between 54 and 67 cm (21" and 26") long, with a wingspan of 115 to 150 cm (45–51"). Recorded weights range from 0.69 to 2 kg (1.5 to 4.4 lb), thus making the common raven one of the heaviest passerines. Birds from colder regions such as the Himalayas and Greenland are generally larger with slightly larger bills, while those from warmer regions are smaller with proportionally smaller bills. Representative of the size variation in the species, ravens from California weighed an average of 784 g (1.728 lb), those from Alaska weighed an average of 1,135 g (2.502 lb) and those from Nova Scotia weighed an average of 1,230 g (2.71 lb). The bill is large and slightly curved, with a culmen length of 5.7 to 8.5 cm (2.2 to 3.3 in), easily one of the largest bills amongst passerines (perhaps only the thick-billed raven has a noticeably larger bill). It has a longish, strongly graduated tail, at 20 to 26.3 cm (7.9 to 10.4 in), and mostly black iridescent plumage, and a dark brown iris. The throat feathers are elongated and pointed and the bases of the neck feathers are pale brownish-grey. The legs and feet are good-sized, with a tarsus length of 6 to 7.2 cm (2.4 to 2.8 in). Juvenile plumage is similar but duller with a blue-grey iris.
Apart from its greater size, the common raven differs from its cousins, the crows, by having a larger and heavier black beak, shaggy feathers around the throat and above the beak, and a wedge-shaped tail. Flying ravens are distinguished from crows by their tail shape, larger wing area, and more stable soaring style, which generally involves less wing flapping. Despite their bulk, ravens are easily as agile in flight as their smaller cousins. In flight the feathers produce a creaking sound that has been likened to the rustle of silk. The voice of ravens is also quite distinct, its usual call being a deep croak of a much more sonorous quality than a crow's call. In North America, the Chihuahuan raven (C. cryptoleucus) is fairly similar to the relatively small common ravens of the American southwest and is best distinguished by the still relatively smaller size of its bill, beard and body and relatively longer tail. All-black carrion crow (C. corone) in Europe may suggest a raven due to their largish bill but are still distinctly smaller and have the wing and tail shapes typical of crows.
In the Faroe Islands, a now-extinct white-and-black colour morph of this species existed, known as the pied raven.
White ravens are occasionally found in the wild. Birds in British Columbia lack the pink eyes of an albino, and are instead leucistic, a condition where an animal lacks any of several different types of pigment, not simply melanin.
Common ravens have a wide range of vocalizations which are of interest to ornithologists. Gwinner carried out important studies in the early 1960s, recording and photographing his findings in great detail. Fifteen to 30 categories of vocalization have been recorded for this species, most of which are used for social interaction. Calls recorded include alarm calls, chase calls, and flight calls. The species has a distinctive, deep, resonant prruk-prruk-prruk call, which to experienced listeners is unlike that of any other corvid. Its very wide and complex vocabulary includes a high, knocking toc-toc-toc, a dry, grating kraa, a low guttural rattle and some calls of an almost musical nature.
Voice, singing & callLike other corvids, ravens can mimic sounds from their environment, including human speech. Non-vocal sounds produced by the common raven include wing whistles and bill snapping. Clapping or clicking has been observed more often in females than in males. If a member of a pair is lost, its mate reproduces the calls of its lost partner to encourage its return.
Distribution & habitatCommon ravens can thrive in varied climates; indeed this species has the largest range of any member of the genus, and one of the largest of any passerine. They range throughout the Holarctic from Arctic and temperate habitats in North America and Eurasia to the deserts of North Africa, and to islands in the Pacific Ocean. In the British Isles, they are more common in Scotland, Wales, northern England and the west of Ireland. In Tibet, they have been recorded at altitudes up to 5,000 m (16,400 ft), and as high as 6,350 m (20,600 ft) on Mount Everest. The population sometimes known as the Punjab raven—described as Corvus corax laurencei (also spelt lawrencii or laurencii) by Allan Octavian Hume but more often considered synonymous with subcorax —is restricted to the Sindh district of Pakistan and adjoining regions of northwestern India. They are generally resident within their range for the whole year. In his 1950 work, Grønlands Fugle [Birds of Greenland], noted ornithologist Finn Salomonsen indicated that common ravens did not overwinter in the Arctic. However, in Arctic Canada and Alaska, they are found year-round. Young birds may disperse locally.
Most common ravens prefer wooded areas with large expanses of open land nearby, or coastal regions for their nesting sites and feeding grounds. In some areas of dense human population, such as California in the United States, they take advantage of a plentiful food supply and have seen a surge in their numbers. On coasts, individuals of this species are often evenly distributed and prefer to build their nest sites along sea cliffs. Common ravens are often located in coastal regions because these areas provide easy access to water and a variety of food sources. Also, coastal regions have stable weather patterns without extreme cold or hot temperatures.
In general, common ravens live in a wide array of environments but prefer heavily contoured landscapes. When the environment changes in vast degrees, these birds will respond with a stress response. The hormone known as corticosterone is activated by the hypothalamic–pituitary–adrenal axis. Corticosterone is activated when the bird is exposed to stress, such as migrating great distances.
Hunting & foodCommon ravens are omnivorous and highly opportunistic: their diet may vary widely with location, season and serendipity. For example, those foraging on tundra on the Arctic North Slope of Alaska obtained about half their energy needs from predation, mainly of microtine rodents, and half by scavenging, mainly of caribou and ptarmigan carcasses.
In some places they are mainly scavengers, feeding on carrion as well as the associated maggots and carrion beetles. With large-bodied carrion, which they are not equipped to tear through as well as birds such as hook-billed vultures, they must wait for the prey to be torn open by another predator or flayed by other means. Plant food includes cereal grains, berries and fruit. They prey on small invertebrates, amphibians, reptiles, small mammals and birds. Ravens may also consume the undigested portions of animal feces, and human food waste. They store surplus food items, especially those containing fat, and will learn to hide such food out of the sight of other common ravens. Ravens also raid the food caches of other species, such as the Arctic fox. They sometimes associate with another canine, the grey wolf, as a kleptoparasite, following to scavenge wolf-kills in winter. Ravens are regular predators at bird nests, brazenly picking off eggs, nestlings and sometimes adult birds when they spot an opportunity. They are considered perhaps the primary natural threat to the nesting success of the critically endangered California condor, since they readily take condor eggs and are very common in the areas where the species is being re-introduced. On the other hand, when they defend their own adjacent nests, they may incidentally benefit condors since they chase golden eagles out of the area that may otherwise prey upon larger nestling and fledging condors. Condors, despite their large size, do not seem to have well developed nest defenses.
Common ravens nesting near sources of human garbage included a higher percentage of food waste in their diet, birds nesting near roads consumed more road-killed vertebrates, and those nesting far from these sources of food ate more arthropods and plant material. Fledging success was higher for those using human garbage as a food source. In contrast, a 1984–1986 study of common raven diet in an agricultural region of south-western Idaho found that cereal grains were the principal constituent of pellets, though small mammals, grasshoppers, cattle carrion and birds were also eaten.
One behavior is recruitment, where juvenile ravens call other ravens to a food bonanza, usually a carcass, with a series of loud yells. In Ravens in Winter, Bernd Heinrich posited that this behavior evolved to allow the juveniles to outnumber the resident adults, thus allowing them to feed on the carcass without being chased away. A more mundane explanation is that individuals co-operate in sharing information about carcasses of large mammals because they are too big for just a few birds to exploit. Experiments with baits however show that such recruitment behaviour is independent of the size of the bait.
Furthermore, there has been research suggesting that the common raven is involved in seed dispersal. In the wild, the common raven chooses the best habitat and disperses seeds in locations best suited for its survival.
Breeding, mating, chicks, juveniles & raiseJuveniles begin to court at a very early age, but may not bond for another two or three years. Aerial acrobatics, demonstrations of intelligence, and ability to provide food are key behaviors of courting. Once paired, they tend to nest together for life, usually in the same location. Instances of non-monogamy have been observed in common ravens, by males visiting a female's nest when her mate is away.
Breeding pairs must have a territory of their own before they begin nest-building and reproduction, and thus aggressively defend a territory and its food resources. Nesting territories vary in size according to the density of food resources in the area. The nest is a deep bowl made of large sticks and twigs, bound with an inner layer of roots, mud, and bark and lined with a softer material, such as deer fur. The nest is usually placed in a large tree or on a cliff ledge, or less frequently in old buildings or utility poles.
Females lay between three and seven pale bluish-green, brown-blotched eggs. Incubation is about 18 to 21 days, by the female only. The male may stand or crouch over the young, sheltering but not actually brooding them. Young fledge at 35 to 42 days, and are fed by both parents. They stay with their parents for another six months after fledging.
In most of their range, egg-laying begins in late February. In colder climates, it is later, e.g. April in Greenland and Tibet. In Pakistan, egg-laying takes place in December. Eggs and hatchlings are preyed on, rarely, by large hawks and eagles, large owls, martens and canids. The adults, which are very rarely preyed upon, are often successful in defending their young from these predators, due to their numbers, large size and cunning. They have been observed dropping stones on potential predators that venture close to their nests.
Common ravens can be very long-lived, especially in captive or protected conditions; individuals at the Tower of London have lived for more than 40 years. Lifespans in the wild are considerably shorter at typically 10 to 15 years. The longest known lifespan of a banded wild common raven was 23 years, 3 months.