Common raven

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"Corvus corax" redirects here. For the German band, see Corvus Corax (band).
For the butterfly called the common raven, see Papilio castor.

Common raven
Temporal range: Middle Pleistocene–Recent
↓
Near the Tower of London, England
Call recorded in Grand Teton National Park

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Corvus
Species:
C. corax
Binomial name
Corvus corax
Subspecies

8–11, see Classification

Common raven range
  Breeding
  Resident
  Non-breeding

The common raven (Corvus corax) is a large all-black

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, the raven 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.

Taxonomy

The common raven was one of the many species originally described, with its

type locality given as Europe, by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae, and it still bears its original name of Corvus corax.[2] It is the type species of the genus Corvus, derived from the Latin word for 'raven'.[3] The specific epithet corax is the Latinized form of the Greek word κόραξ, meaning 'raven' or 'crow'.[4]

The modern English word raven has cognates in many other

Proto-Germanic *khrabanas.[6] An old Scottish word corby or corbie, akin to the French corbeau, has been used for both this bird and the carrion crow.[7] Collective nouns for a group of ravens (or at least the common raven) include "unkindness"[8] and "conspiracy".[9]

Classification

The closest relatives of the common raven are the brown-necked raven (C. ruficollis), the pied crow (C. albus) of Africa, and the Chihuahuan raven (C. cryptoleucus) of the North American Southwest.[10] While some authorities have recognized as many as 11 subspecies,[11] others recognize only eight:[12]

Common name Scientific name Image Distribution Notes
northern raven C. c. principalis Northern North America and Greenland It has a large body and the largest bill, its plumage is strongly glossy, and its throat hackles are well-developed.[13]
western raven C. c. sinuatus South-central North America and Central America It is smaller, with a smaller and narrower bill than C. c. principalis. Populations in the far southwestern U.S. and northwestern Mexico (including the Revillagigedo Islands) are the smallest ravens in North America. They are sometimes included in C. c. sinuatus, while other authorities recognize them as a separate subspecies, the southwestern raven (C. c. clarionensis).[11]
North Atlantic raven C. c. varius Iceland and the Faroe Islands It is less glossy than C. c. principalis or the nominate subspecies C. c. corax, is intermediate in size, and the bases of its neck feathers are whitish (not visible at a distance). An
extinct white-and-black colour morph found only on the Faroe Islands was known as the pied raven (C. c. varius morpha leucophaeus; the black colour morph's scientific name is C. c. varius morpha typicus).[13]
North African raven C. c. tingitanus North Africa and the Canary Islands It is the smallest subspecies, with the shortest throat hackles and a distinctly oily plumage gloss. Its bill is short but markedly stout, and the
culmen is strongly arched. The Canary Islands raven is browner than the North African raven, leading some authorities to recognize them as separate subspecies, with the North African raven maintaining the name C. c. tingitanus and the Canary Islands raven known as C. c. canariensis.[11]
North Eurasian raven C. c. corax From Europe eastwards to Lake Baikal, south to the Caucasus region and northern Iran It has a relatively short, arched bill. The population in southwestern Europe (including the Balearic Islands, Corsica and Sardinia) has an even more arched bill and shorter wings than the "typical" nominate, leading some authorities to recognize it as a separate subspecies, the Hispanic raven (C. c. hispanus).[11]
South Eurasian raven C. c. subcorax From Greece eastwards to northwestern India, Central Asia and western China, though not in the Himalayan region It is larger than the nominate subspecies, but has relatively short throat hackles. Its plumage is generally all black, though its neck and breast have a brownish tone similar to that of the brown-necked raven; this is more evident when the plumage is worn. The bases of its neck feathers, although somewhat variable in colour, are often almost whitish.

The name C. c. laurencei (also spelt lawrencii or laurencii) is sometimes used instead of C. c. subcorax.[11] It is based on the population from Sindh described by Hume in 1873[14] and is sometimes preferred, since the type specimen of subcorax collected by Nikolai Severtzov is possibly a brown-necked raven.[15]

The population of this subspecies restricted to the Sindh district of Pakistan and the adjoining regions of northwestern India is sometimes known as the Punjab raven.[16][17]

Tibetan raven C. c. tibetanus The Himalayas It is the largest and glossiest subspecies, with the longest throat hackles. Its bill is large, but less imposing than that of C. c. principalis and the bases of its neck feathers are grey.[13]
Kamchatkan raven C. c. kamtschaticus Northeastern Asia Intergrades into the nominate subspecies in the Lake Baikal region. It is intermediate in size between C. c. principalis and C. c. corax and has a distinctly larger and thicker bill than the nominate subspecies does.[13]

Evolutionary history

The common raven evolved in the

Holarctic clade, found across the rest of the Northern Hemisphere. Birds from both clades look alike, but the groups are genetically distinct and began to diverge about two million years ago.[19][20]

The findings indicate that based on

paraphyletic.[21]

One explanation for these genetic findings is that common ravens settled in California at least two million years ago and became separated from their relatives in Europe and Asia during a glacial period. One million years ago, a group from the California clade evolved into a new species, the Chihuahuan raven. Other members of the Holarctic clade arrived later in a separate migration from Asia, perhaps at the same time as humans.[22]

A 2011 study suggested that there are no restrictions on gene flow between the Californian and Holarctic common raven groups, and that the lineages can remerge, effectively reversing a potential speciation.[23]

A recent study of raven mitochondrial DNA showed that the isolated population from the Canary Islands is distinct from other populations.[24] The study did not include any individuals from the North African population,[24] and its position is therefore unclear, though its morphology is very close to the population of the Canaries (to the extent that the two are often considered part of a single subspecies).[12]

Description

For physiology, see Common raven physiology.
In sunlight, the plumage can display a blue or purple sheen which is a result of iridescence.

A mature common raven ranges between 54 and 71 cm (21 and 28 in) and has a

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).[34][35] Juvenile plumage is similar but duller with a blue-grey iris.[36]

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.[37] 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.[16] 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.[38]

In the Faroe Islands, a now-extinct white-and-black colour morph of this species existed, known as the pied raven;[39] the ordinary black-coloured common ravens remain widespread in the archipelago.[40]

White ravens are occasionally found in the wild. Birds in

leucistic, a condition where an animal lacks any of several different types of pigment, not simply melanin.[41]

Vocalising

Common ravens have a wide range of

ornithologists. Gwinner carried out important studies in the early 1960s, recording and photographing his findings in great detail.[42] 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.[42]

Like other corvids, the common raven 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.[43]

Distribution and habitat

Two juveniles in Iceland

The common raven can thrive in varied climates; it has the largest range of any member of the genus,

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.[37] 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.[45][47] 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[14]—is restricted to the Sindh district of Pakistan and adjoining regions of northwestern India.[16][17] 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.[48] However, in Arctic Canada and Alaska, they are found year-round.[49][50][51] Young birds may disperse locally.[52]

Common Ravens panting to cool down in 110 °F (43 °C) heat in Palm Desert, California

In the United Kingdom, the common raven's range is currently increasing. It favours mountainous or coastal terrain, but can also be found in parks with tall trees suitable for use as habitation. Its population is at its most dense in the north and west of the country, though the species is expanding its population southwards.[53]

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.[54] On coasts, individuals of this species are often evenly distributed and prefer to build their nest sites along sea cliffs.[55] Common ravens are often located in coastal regions because these areas provide easy access to water and a variety of food sources.[55] 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.[56] Corticosterone is activated when the bird is exposed to stress, such as migrating great distances.

Behaviour

Group of ravens gathered around dead member

Common ravens usually travel in mated pairs, although young birds may form flocks. Relationships between common ravens are often quarrelsome, yet they demonstrate considerable devotion to their families.[57]

Predation

Owing to its size, gregariousness and its defensive abilities, the common raven has few natural predators. Predators of its eggs include owls, martens, and sometimes eagles. Ravens are quite vigorous at defending their young and are usually successful at driving off perceived threats. They attack potential predators by flying at them and lunging with their large bills. Humans are occasionally attacked if they get close to a raven nest, though serious injuries are unlikely. There are a few records of predation by large birds of prey. Their attackers in America have reportedly included great horned owls, northern goshawks, bald eagles, golden eagles and red-tailed hawks. It is possible that the two hawk species only attack young ravens; in one instance a peregrine falcon swooped at a newly fledged raven but was chased off by the parent ravens.[58][59][60][61]

In

Steller's sea-eagles, eastern imperial eagles and gyrfalcons.[62][63][64][65][66] Because they are potentially hazardous prey for raptorial birds, raptors must usually take them by surprise and most attacks are on fledgling ravens. More rarely still, large mammalian predators such as lynxes, coyotes and cougars have also attacked ravens. This principally occurs at a nest site and when other prey for the carnivores are scarce. Ravens are highly wary around novel carrion sites and, in North America, have been recorded waiting for the presence of American crows and blue jays before approaching to eat.[67]

Breeding

Young on a nest – Hvítserkur, Iceland
Eggs of Corvus corax

Juveniles 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 behaviours of courting. Once paired, they tend to nest together for life, usually in the same location.[57] Instances of non-monogamy have been observed in common ravens, by males visiting a female's nest when her mate is away.[68]

Breeding pairs must have a territory of their own before they begin nest-building and reproduction, and thus they aggressively defend a territory and its food resources. Nesting territories vary in size according to the density of food resources in the area.[28] 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.[69]

Females lay between three and seven pale bluish-green, brown-blotched eggs.

brooding them.[70] Young fledge at 35 to 42 days, and are fed by both parents. They stay with their parents for another six months after fledging.[71]

In most of their range, egg-laying begins in late February, but it can be as late as April in colder climates such as

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.[67] They have been observed dropping stones on potential predators that venture close to their nests.[72]

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.[28] Their lifespans in the wild are shorter, typically 10 to 15 years. The longest known lifespan of a banded wild common raven was 23 years, 3 months,[73] which among passerines only is surpassed by a few Australian species such as the satin bowerbird.[74]

Feeding

Feeding

Common ravens are

caribou and ptarmigan carcasses.[76]

In some places they are mainly

kleptoparasite, following to scavenge wolf-kills in winter.[81] 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.[82]

Flock feeding at a garbage dump

Common ravens nesting near sources of human

Fledging success was higher for those using human garbage as a food source.[83] In contrast, a 1984–1986 study of common raven diet in an agricultural region of southwestern Idaho found that cereal grains were the principal constituent of pellets, though small mammals, grasshoppers, cattle carrion and birds were also eaten.[84]

One behaviour 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 behaviour evolved to allow the juveniles to outnumber the resident adults, thus allowing them to feed on the carcass without being chased away.[85] 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.[68] Experiments with baits however show that such recruitment behaviour is independent of the size of the bait.[86]

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.[55]

Intelligence

See also: Bird intelligence and Corvidae § Intelligence

The brain of the common raven is among the largest of any bird species. Specifically, their

cognitive processes such as imitation and insight.[87]

Dilapidated Nike Missile radar dome in Alaska with an evening roost

Linguist Derek Bickerton, building on the work of biologist Bernd Heinrich, has argued that ravens are one of only four known animals (the others being bees, ants, and humans) who have demonstrated displacement, the capacity to communicate about objects or events that are distant in space or time. Subadult ravens roost together at night, but usually forage alone during the day. However, when one discovers a large carcass guarded by a pair of adult ravens, the unmated raven will return to the roost and communicate the find. The following day, a flock of unmated ravens will fly to the carcass and chase off the adults. Bickerton argues that the advent of linguistic displacement was perhaps the most important event in the evolution of human language, and that ravens are the only other vertebrate to share this with humans.[88]

One experiment designed to evaluate insight and

trial-and-error learning." This supports the hypothesis that common ravens are 'inventors', implying that they can solve problems. Many of the feats of common ravens were formerly argued to be stereotyped innate behaviour, but it now has been established that their aptitudes for solving problems individually and learning from each other reflect a flexible capacity for intelligent insight unusual among non-human animals.[89] Another experiment showed that some common ravens could intentionally deceive their conspecifics.[90]

A study published in 2011 found that ravens can recognise when they are given an unfair trade during reciprocal interactions with conspecifics or humans, retaining memory of the interaction for a prolonged period of time. Birds that were given a fair trade by experimenters were found to prefer interacting with these experimenters compared to those that did not.[91] Furthermore, ravens in the wild have also been observed to stop cooperating with other ravens if they observe them cheating during group tasks.[92]

Common ravens have been observed calling wolves to the site of dead animals. The wolves open the carcass, leaving the scraps more accessible to the birds.[87] They watch where other common ravens bury their food and remember the locations of each other's food caches, so they can steal from them. This type of theft occurs so regularly that common ravens will fly extra distances from a food source to find better hiding places for food.[93] They have also been observed pretending to make a cache without actually depositing the food, presumably to confuse onlookers.[94]

Common ravens are known to steal and cache shiny objects such as pebbles, pieces of metal, and golf balls. One theory is that they hoard shiny objects to impress other ravens.[95] Other research indicates that juveniles are deeply curious about all new things, and that common ravens retain an attraction to bright, round objects based on their similarity to bird eggs. Mature birds lose their intense interest in the unusual, and become highly neophobic.[96]

The first large-scale assessment of ravens' cognitive abilities suggests that, by four months of age, ravens do about as well as adult chimps and orangutans on tests of causal reasoning, social learning, theory of mind, etc.[97]

Play

There has been increasing recognition of the extent to which birds engage in play. Juvenile common ravens are among the most playful of bird species. They have been observed to slide down snowbanks, apparently purely for fun. They even engage in games with other species, such as playing catch-me-if-you-can with wolves, otters and dogs.[98] Common ravens are known for spectacular aerobatic displays, such as flying in loops or interlocking talons with each other in flight.[99][100]

They are also one of only a few wild animals who make their own toys. They have been observed breaking off twigs to play with socially.[101]

Relationship with humans

Conservation and management

colour morph from the Faroe Islands

Compared to many smaller Corvus species (such as American crow), ravens prefer undisturbed mountain or forest habitat or rural areas over urban areas.[102] In other areas, their numbers have increased dramatically and they have become agricultural pests. Common ravens can cause damage to crops, such as nuts and grain, or can harm livestock, particularly by killing young goat kids, lambs and calves.[103] Ravens generally attack the faces of young livestock, but the more common raven behaviour of scavenging may be misidentified as predation by ranchers.[104]

In the western Mojave Desert, human settlement and land development have led to an estimated 16-fold increase in the common raven population over 25 years. Towns, landfills, sewage treatment plants and artificial ponds create sources of food and water for scavenging birds. Ravens also find nesting sites in utility poles and ornamental trees, and are attracted to roadkill on highways. The explosion in the common raven population in the Mojave has raised concerns for the desert tortoise, a threatened species. Common ravens prey upon juvenile tortoises, which have soft shells and move slowly.[54] Plans to control the population have included shooting and trapping birds, as well as contacting landfill operators to ask that they reduce the amount of exposed garbage.[105] A hunting bounty as a method of control was historically used in Finland from the mid-18th century until 1923.[106] Culling has taken place to a limited extent in Alaska, where the population increase in common ravens is threatening the vulnerable Steller's eider (Polysticta stelleri).[107]

Ravens, like other corvids, are definitive hosts of West Nile Virus (WNV).[108] The transmission can be from infected birds to humans, and ravens are susceptible to WNV. However, in a 2010 study, it was shown that the California Common Ravens did not have a high positivity rate of WNV.[109]

Cultural depictions

Bill Reid's sculpture The Raven and the First Men, showing part of a Haida creation myth. Museum of Anthropology, University of British Columbia.
See also: Cultural depictions of ravens

Across its range in the Northern Hemisphere, and throughout human history, the common raven has been a powerful symbol and a popular subject of mythology and folklore.

In some Western traditions, ravens have long been considered to be birds of ill omen, death and evil in general, in part because of the negative symbolism of their all-black plumage and the eating of carrion.[110] In Sweden, ravens are known as the ghosts of murdered people, and in Germany as the souls of the damned. In Danish folklore, valravne that ate a king's heart gained human knowledge, could perform great malicious acts, could lead people astray, had superhuman powers, and were "terrible animals".[111]

It continues to be used as a symbol in areas where it once had mythological status: as the

kings of Bhutan wear the Raven Crown), official bird of the Yukon territory,[113] and on the coat of arms of the Isle of Man (once a Viking colony).[114]

In Persia and Arabia the raven was held as a bird of bad omen but a 14th-century Arabic work reports use of the raven in falconry.[115]

The modern

bynames and personal names.[117]

A valkyrie speaks with a raven in a 19th-century illustration of the Old Norse poem Hrafnsmál ("raven song") by Frederick Sandys

Mythology

Main article:
Raven in mythology

In

creator god. Related beliefs are widespread among the peoples of Siberia and northeastern Asia.[118] The Kamchatka Peninsula, for example, was supposed to have been created by the raven god Kutkh.[119] There are several references to common ravens in the Old Testament of the Bible and it is an aspect of Mahakala in Bhutanese mythology.[112]

In

Morrígan alighted on the hero Cú Chulainn's shoulder in the form of a raven after his death.[123] In Welsh mythology they were associated with the Welsh god Brân the Blessed, whose name translates to "crow". According to the Mabinogion, Brân's head was buried in the White Hill of London as a talisman against invasion.[124]

A legend developed that England would not fall to a foreign invader as long as there were ravens at the Tower of London; although this is often thought to be an ancient belief, the official Tower of London historian, Geoff Parnell, believes that this is actually a romantic Victorian invention.[125]

In the

Jesus tells a parable using the raven to show how people should rely on God for their needs and not riches (Luke 12:24).[127] The raven is also mentioned in the Quran at the story of Cain and Abel. Adam's firstborn son Cain kills his brother Abel, but he does not know what to do with the corpse: "Then Allah sent a raven scratching up the ground, to show him how to hide his brother's naked corpse. He said: Woe unto me! Am I not able to be as this raven and so hide my brother's naked corpse? And he became repentant."[128]

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