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common raven



Corvus corax 22-27″ (55-68 cm). Note the wedge-shaped tail. Much larger than American Crow; has a heavier voice and is inclined to be not as gregarious, often solitary. Hawklike in flight, it alternates flapping and sailing, gliding on flat wings (Crow glides with a slight upward dihedral). When it is perched and not too distant, note the "goiter" look created by the shaggy throat feathers and the heavier "Roman-nose" bill.

Voice: A croaking cr-r-ruck or prruk; also a metallic tok.

Range: Widespread in N. America, Eurasia, Africa.

Habitat: Boreal and mountain forests, coastal cliffs, tundra.

 
 
Wikipedia: Common Raven
"Corvus Corax" redirects here. For the band, see Corvus Corax (band).
Common Raven
Common Raven at Bryce Canyon National Park, USA
Common Raven at
Bryce Canyon National Park, USA
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Corvus
Species: C. corax
Binomial name
Corvus corax
Linnaeus, 1758
Common Raven range
Common Raven range
Subspecies
  • C. c. corax
  • C. c. varius
  • C. c. subcorax
  • C. c. tingitanus
  • C. c. tibetanus
  • C. c. kamtschaticus
  • C. c. principalis
  • C. c. sinuatus

The Common Raven (Corvus corax), also known as the Northern Raven, is a large all-black passerine bird in the crow family. Found across the northern hemisphere, it is the most widely distributed of all corvids. There are eight known subspecies with little variation in appearance, however recent research has demonstrated significant genetic differences between populations from different 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 is between 56 and 69 cm (22 to 27 inches) in length, with recorded weights ranging from 0.69 to 1.63 kg (1.5 to 3.6 pounds). Common Ravens typically live about 10 to 15 years in the wild, although lifespans of up to 40 years have been recorded. Young birds may travel in flocks, but later mate for life, with each mated pair defending a territory.

The Common Raven has coexisted with humans for thousands of years, and in some areas has been so successful that it is considered a pest. Part of its success comes from its omnivorous diet; Common Ravens are extremely versatile and opportunistic in finding sources of nutrition, feeding on carrion, insects and food waste, in addition to cereal grains, berries, fruit and small animals.

Some remarkable feats of problem-solving have been observed in the species, leading to the belief that it is highly intelligent. Over the centuries, it has been the subject of mythology, folklore, art and literature. In many indigenous cultures, including those of Scandinavia, ancient Ireland and Wales, Bhutan and the northwest coast of North America, the Common Raven has been revered as a spiritual figure or god.[2]

Taxonomy

The Common Raven was one of the many species originally described by Linnaeus in his 18th century work, Systema Naturae, and it still bears its original name of Corvus corax.[3] It is the type species of the genus Corvus, derived from the Latin for "raven".[4] The specific epithet, corax/κοραξ, is the Greek word for "raven" or "crow".[5]The name "raven" has been applied to several other (generally large) species of the genus Corvus, though they are not necessarily closely related to Corvus corax. Some, such as the Australian Raven and Forest Raven are clearly closer to the other Australian crows.[6] The original raven is now called the Common or Northern Raven.[7]

The word "raven" is similar in many old Germanic languages; the Old English word for a raven was hræfn; in Old Norse it was hrafn and Old High German (h)raban,[8] all these words are descended from a Proto-Germanic *khrabanas.[9] An old Scottish word corby or corbie, akin to the French corbeau, has been used for both this bird and the Carrion Crow.[10]

Classification

The closest relatives of the Common Raven are the Brown-necked Raven (C. ruficollis) and the Pied Crow (C. albus) of Africa, and the Chihuahuan Raven (C. cryptoleucus) of the North American southwest.[11] There are eight recognized subspecies:

  • C. c. corax (the nominate subspecies) occurs from Europe eastwards to Lake Baikal, south to the Caucasus region and northern Iran. It has a relatively short, arched bill.
  • C. c. varius occurs in Iceland and the Faroe Islands. It is less glossy than C. c. principalis or nominate corax, is intermediate in size, and the bases of its neck feathers are whitish (not visible at a distance). An extinct color morph found only on the Faroes is known as Pied Raven.
A North Atlantic Common Raven (C. c. varius) in flight over Seltjarnarnes, Iceland
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A North Atlantic Common Raven (C. c. varius) in flight over Seltjarnarnes, Iceland
  • C. c. subcorax occurs from Greece eastwards to north-west India, Central Asia and western China though not the Himalayan region. It is larger than the nominate form, but has relatively short throat feathers (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 more evident when the plumage is worn. The bases of its neck feathers, though somewhat variable in colour, are often almost whitish.
  • C. c. tingitanus occurs in 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. When worn, its plumage fades to dark brown on the head and body.
  • C. c. tibetanus occurs in 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.
  • C. c. kamtschaticus occurs in north-eastern Asia, intergrading into the nominate subspecies in the Baikal region. It is intermediate in size between C. c. principalis and C. c. corax and has a distinctly larger and thicker bill than does the nominate race.
  • C. c. principalis occurs in northern North America and Greenland. It has a large body and the largest bill, its plumage is strongly glossed, and its throat hackles are well developed.
  • C. c. sinuatus, the Western Raven, occurs in south-central USA and Central America. It is smaller, with a smaller and narrower bill than C. c. principalis.

Evolutionary history

The Common Raven evolved in the Old World and crossed the Bering land bridge into North America.[12] Recent genetic studies, which examined the DNA of Common Ravens from across the world, have determined that the birds fall into at least two clades: a California clade, found only in the southwestern United States, and a 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.[13][14]

The findings indicate that based on mitochondrial DNA, Common Ravens from the rest of the United States are more closely related to those in Europe and Asia than they are to those in the California clade, and that Common Ravens in the California clade are more closely related to the Chihuahuan Raven (C. cryptoleucus) than they are to those in the Holarctic clade.[13] Ravens in the Holarctic clade are more closely related to the Pied Crow (C. albus) than they are to the California clade.[15] Thus, the Common Raven species as traditionally delimited is considered to be paraphyletic.[15]

One explanation for these surprising 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 an ice age. 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.[16]

A recent study of raven mitochondrial DNA showed that members of the C. c. tingitanus subspecies have significant genetic differences from the rest of the Holarctic clade. This subspecies occurs only in North Africa and the Canary islands. The study also demonstrated that C. c. tingitanus ravens do not interbreed with other subspecies.[17]

A taxonomic solution would be to consider at least sinuatus a distinct species again. In fact, it is in many aspects intermediate between the Common Raven proper and the Chihuahuan Raven and was considered distinct enough to warrant a common name of its own, Western Raven, in the early 20th century already. Whether the Western Raven ought to be united with the Chihuahuan Raven or not could be resolved by studies of gene flow and ecological displacement. It is notable that the Brown-necked Raven and Dwarf Ravens of Africa seem to be offshoots of the Common Raven-Pied Crow complex that evolved in parallel in many (mainly ecological) aspects to the Western and Chihuahuan Ravens. Thus, no matter what the eventual taxonommic treatment will be, the Common Raven (and to a lesser degree, Pied Crow) ancestral stock had a tendency to expand into more arid and (sub)tropical climates from humid and temperate regions, producing distinct lineages. Considering the distinctness of tingitanus, such a parallel evolution of ravens adapted to Mediterranean climates has happened 4 times from the time where the ancestors of Common Ravens and Pied Crows had not yet fully diverged until today.

Description

The plumage of the Common Raven is glossy and may have a blue or purple tinge.
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The plumage of the Common Raven is glossy and may have a blue or purple tinge.

A mature Common Raven is between 56 and 69 cm (22 to 27 inches) in length, with a wingspan of 115 to 130 cm (45 to 51 in). Recorded weights range from 0.69 to 1.63 kg (1.5 to 3.6 lb),[18] making it 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.[19] The bill is large and slightly curved. It has a longish, strongly graduated tail, 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. Juvenile plumage is similar but duller with a blue-grey iris.[20]

Apart from its greater size, the Common Raven differs from its cousins, the crows, by having a larger and heavier beak, a shaggy throat, and a wedge-shaped tail.[21] The species has a distinctive, deep, hollow pruk-pruk-pruk 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.[22]

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.[18] Lifespans in the wild are considerably shorter: typically only 10 to 15 years. The longest known lifespan of a banded wild Common Raven was 13 years.[23]

Distribution and habitat

Two juveniles in Iceland
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Two juveniles in Iceland

Common Ravens can thrive in varied climates; indeed this species has the largest range of any member of the genus.[24][25] 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, northern England and the west of Ireland.[21] In Tibet, they have been recorded from altitudes up to 5,000 m (16,400 ft), and from as high as 6,350 m (20,600 ft) on Mount Everest.[25]

Except in Arctic habitats,[26] they are generally resident within their range for the whole year. Young birds may disperse locally.[27]

In the Faroe Islands a now extinct colour-morph of this species existed, known as the Pied Raven.[28]

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.[29]

Behavior

Common Ravens usually travel in mated pairs, although young birds may form flocks. Relationships between Common Ravens are often quarrelsome, however they demonstrate considerable devotion to their families.[30]

Diet

A flock of Common Ravens feeding at a garbage dump
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A flock of Common Ravens feeding at a garbage dump

Common Ravens are omnivorous and highly opportunistic: their diet may vary widely with location, season and serendipity.[31] 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.[32]

In some places they are mainly scavengers, feeding on carrion as well as the associated maggots and carrion beetles.[33] Plant food includes cereal grains, berries and fruit. They prey on small invertebrates, amphibians, reptiles, small mammals and birds.[34] 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.[35] They also raid the food caches of other species, such as the Arctic Fox.[36] They may also associate with another canine, the Grey Wolf, as a kleptoparasite, following to scavenge carcasses in winter.[37]

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.[38] In contrast, a 1984-1986 study of Common Raven diet in south-western Idaho, an agricultural region, found that cereal grains were the principal constituent of pellets, though small mammals, grasshoppers, cattle carrion and birds were also eaten.[39]

One behaviour used by young birds is recruitment, where dominant 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.[40] 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 eat.[41]

Breeding

Young Common Ravens on a nest - Hvítserkur, Iceland
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Young Common Ravens on a nest - Hvítserkur, Iceland

Juveniles begin to court at a very early age, but may not bond for another two or three years. Aerial acrobatics and 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.[30] Sexual infidelity has been observed in Common Ravens, by males visiting a female's nest when her mate is away.[42]

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.[18] The nest is a deep bowl made of large sticks and twigs, bound together 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.[43]

Females lay between three to seven pale bluish-green, brown-blotched eggs.[21] Incubation is about 18 to 21 days, by the female only. However, the male may stand or crouch over the young, sheltering but not actually brooding them.[44] Young fledge at 35 to 42 days, and are fed by both parents. They stay with their parents for another six months after fledging.[45]

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.[25]

Vocalization

Common Raven
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Common Raven
Common Raven at the norwegian Island of Runde
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Common Raven at the norwegian Island of Runde

Like other corvids, Ravens can mimic sounds from their environment, including human speech. They have a wide range of vocalizations, which remain an object of interest to ornithologists. Gwinner carried out important studies in the early 1960s, recording and photographing his findings in great detail.[22]

Fifteen to thirty 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. 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.[46]

Intelligence

See also: Bird intelligence and Corvidae#Corvid_intelligence


“ Crows, ravens, magpies, and jays are not just feathered machines, rigidly programmed by their genetics. Instead, they are beings that, within the constraints of their molecular inheritance, make complex decisions and show every sign of enjoying a rich awareness. ”

—Candace Savage[47]

Common Ravens have among the largest brains of any bird species. Specifically, their hyperpallium is large (See avian pallium). For an avian, they display ability in problem-solving, as well as other cognitive processes, such as imitation and insight.[47]

One experiment designed to evaluate insight and problem-solving ability involved a piece of meat attached to a string hanging from a perch. In order to reach the food, the bird needed to stand on the perch, pull the string up a little at a time, and step on the loops to gradually shorten the string. Four out of five Common Ravens eventually succeeded, and "the transition from no success (ignoring the food or merely yanking at the string) to constant reliable access (pulling up the meat) occurred with no demonstrable trial-and-error learning".[48]

Common Ravens have been observed to manipulate others into doing work for them, such as by calling wolves and coyotes to the site of dead animals. The canines open the carcass, making it more accessible to the birds.[47] 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 in order to find better hiding places for food.[49] They have also been observed pretending to make a cache without actually depositing the food, presumably to confuse onlookers.[50]

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 in order to impress other ravens.[51] 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.[52]

In recent years, biologists have begun to recognize that 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 and dogs.[53] Common Ravens are known for spectacular acrobatic displays, such as flying in loops.[54]

Relationship with humans

Conservation and management

Common Ravens are very widely distributed and are not in danger of extinction. In some parts of their range, there have been localised declines due to habitat loss and direct persecution. 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 damage livestock, particularly by pecking out the eyes of newborn lambs and calves.[55]

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 are slow-moving.[29] 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.[56] A hunting bounty as a method of control was historically used in Finland from the mid-18th century until 1923.[57] 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).[58]

Cultural references

Bill Reid's sculpture The Raven and The First Men, showing part of a Haida creation myth. Museum of Anthropology, University of British Columbia.
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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 and Raven in mythology

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.

It has long been considered a bird of ill omen and associated with death. As a carrion eater known to feed on humans killed by warfare or execution, the Common Raven became associated with the dead and with lost souls; in Sweden, ravens are known as the ghosts of murdered people, and in Germany as the souls of the damned.[59]

Many indigenous peoples of the Pacific Northwest Coast of North America revered it as a god; in Tlingit and Haida cultures, Raven was both a Trickster and Creator god. The Vikings believed that ravens Hugin and Munin sat on the god Odin's shoulders and saw and heard all,[60] and a Raven banner standard was carried by such Viking figures as the Norse Jarls of Orkney,[61] King Canute the Great of England, Norway and Denmark,[62] and Harald Hardrada.[63] There are several references to Common Ravens in the Old Testament of the Bible and it is an aspect of Mahakala in Bhutanese mythology.[64]

In the British Isles, ravens were also symbolic to the Celts. In Irish mythology, the goddess Morrígan alighted on the hero Cú Chulainn's shoulder in the form of a raven after his death.[65] In Welsh mythology they were associated with the Welsh god Bran the Blessed, whose name translates to "raven." According to the Mabinogion, Bran's head was buried in the White Hill of London as a talisman against invasion.[66] A legend later developed that England would not fall to a foreign invader so long as there were ravens at the Tower of London; although this is often thought to be an ancient belief, recent research has shown no trace of the legend before the 19th century, and it is now thought to be a romantic Victorian invention drawn from the legend of Bran the Blessed. In fact, the Tower has lacked ravens for long periods in the past; they were last reintroduced after World War II. The government now maintains several birds on the grounds of the Tower, either for insurance or to please tourists (or both).[67] These birds have the primary feathers of one wing clipped periodically to ensure that they cannot leave.

As in traditional mythology and folklore, so the Common Raven features frequently in more modern writings such as the works of William Shakespeare, and, perhaps most famously, in the poem "The Raven" by Edgar Allan Poe. Modern literature too has seen ravens in the works of Charles Dickens,[68] J. R. R. Tolkien,[69] Stephen King,[70] and Joan Aiken[71][72][73][74] among others. It continues to be used as a symbol in areas where it once had mythological status: as the National Bird of Bhutan,[64] Official Bird of the Yukon territory,[75] on the Coat of Arms of the Isle of Man (once a Viking colony),[76] and even as the emblem of the Baltimore Ravens American football team.

References

  1. ^ BirdLife International (2004). Corvus corax. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes justification for why this species is of least concern
  2. ^ Jones, Noragh (1995). Power of Raven, Wisdom of Serpent. Floris Books. ISBN 0-9402-6266-5. 
  3. ^ (Latin) Linnaeus, C (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.. Holmiae. (Laurentii Salvii)., 824. 
  4. ^ Simpson, D.P. (1979). Cassell's Latin Dictionary, 5, London: Cassell Ltd., 883. ISBN 0-304-52257-0. 
  5. ^ Liddell, Henry George and Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 0-19-910207-4. 
  6. ^ Goodwin. p69
  7. ^ Monroe B.L. Jr, Sibley C.G. (1993). A World Checklist of Birds. Yale University Press, 400. 
  8. ^ "Raven". Oxford English Dictionary (2nd edition). (1989). Ed. J. Simpson, E. Weiner (eds). Oxford: Clarendon Press. ISBN 0-19-861186-2. 
  9. ^ Raven. Online Etymology Dictionary. Retrieved on 2007-05-14.
  10. ^ Goodwin. p144
  11. ^ Goodwin. p70-72
  12. ^ Marzluff and Angell p86
  13. ^ a b
  14. ^ Omland KE, Tarr CL, Boarman WI, Marzluff JM, Fleischer RC (2000). "Cryptic genetic variation and paraphyly in ravens.". Proceedings of the Royal Society Biological Sciences Series B (267): 2475-82. 
  15. ^ a b Feldman, Christopher R. (March 2005). "Phylogenetics of the common raven complex (Corvus: Corvidae) and the utility of ND4, COI and intron 7 of the β-fibrinogen gene in avian molecular systematics". Zoologica Scripta 34 (2). DOI:10.1111/j.1463-6409.2005.00182.x. 
  16. ^ Marzluff and Angell p86-87
  17. ^ Baker, Jason M. (January 2006). "Canary Island Ravens Corvus corax tingitanus have distinct mtDNA". Ibis 148 (1). DOI:10.1111/j.1474-919X.2006.00493.x. 
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  19. ^ Goodwin. p138-139
  20. ^ Goodwin. p138
  21. ^ a b c
  22. ^ a b (German) Gwinner, E. (1964). "Untersuchungen über das ausdrucks und Sozialverhalten des Kolkraben (Corvus corax L.)". Zeitschrift für Tierpsychologie 21 (6): 657-748. 
  23. ^ Clapp, Roger B.; M. Kathleen Klimkiewicz and Anthony G. Futcher (1983). "Longevity records of North American birds: Columbidae through Paridae". Journal of Field Ornithology 54 (2): 123–137. Retrieved on 2007-05-16. 
  24. ^ Goodwin. p70
  25. ^ a b c Madge, Steve [1994] (1999). Crows and jays : a guide to the crows, jays and magpies of the world, Helm Identification Guides. London: Christopher Helm. ISBN 0-7136-3999-7. 
  26. ^ Salomonsen, Finn (1950). Gronlands Fugle = Birds of Greenland. Copenhagen: Munksgaard. LCCN a+51-710. 
  27. ^ Goodwin. p139
  28. ^ (German)Droste, Ferdinand Baron von (1869). "Vogelfauna der Färöer (Färöernes Fuglefauna af Sysselmaand Müller 1862.) Aus dem Dänischen übersetzt und mit Anmerkungen versehen. Teil 1.". J. Ornithol. 17 (2): 107-118. DOI:10.1007/BF02261546. 
  29. ^ a b
  30. ^ a b
  31. ^ Nogales, Manuel; Elizabeth C. Hernández (1997). "Diet of Common Ravens on El Hierro, Canary Islands". Journal of Field Ornithology 68 (3): 382-391. Retrieved on 2007-05-16. 
  32. ^ Temple, Stanley A. (March 1974). "Winter food habits of Ravens on the Arctic Slope of Alaska". Arctic 27 (1): 41-46. Retrieved on 1007-05-16. 
  33. ^ Nelson, A.L. (January 1934). "Some early summer food preferences of the American Raven in southeastern Oregon". Condor 36 (1): 10-15. Retrieved on 2007-05-16. 
  34. ^ Gaston, A.J. (1996). "Predation by Ravens Corvus corax on Brunnich's Guillemot Uria lomvia eggs and chicks and its possible impact on breeding site selection". Ibis 138: 742-748. 
  35. ^ Goodwin. p139
  36. ^ Careau, Vincent; Nicolas Lecomte, Jean-François Giroux and Dominique Berteaux (January 2007). "Common ravens raid arctic fox food caches". Journal of Ethology 25 (1): 79-82. DOI:10.1007/s10164-006-0193-7. 
  37. ^ Stahler, Daniel; Bernd Heinrich and Douglas Smith (August 2002). "Common ravens, Corvus corax, preferentially associate with grey wolves, Canis lupus, as a foraging strategy in winter". Animal Behaviour 64 (2): 283-290. DOI:10.1006/anbe.2002.3047. 
  38. ^ Kristan, William B.; William I. Boarman and John J. Crayon (March 2004). "Diet composition of common ravens across the urban-wildland interface of the West Mojave Desert". Wildlife Society Bulletin 32 (1): 244-253. DOI:10.2193/0091-7648(2004)32[244:DCOCRA]2.0.CO;2. 
  39. ^ Engel, Kathleen A.; Leonard S. Young (May 1989). "Spatial and temporal patterns in the diet of Common Ravens in southwestern Idaho.". Condor 91 (2): 372-378. Retrieved on 2005-05-16. 
  40. ^ Heinrich, Bernd (1989). Ravens in Winter. New York: Summit Books. ISBN 0-671-67809-4. 
  41. ^ Davies, Gareth Huw. Bird Brains. The Life of Birds. PBS. Retrieved on 2007-05-11.
  42. ^ Heinrich, B. (1999). Mind of the Raven: Investigations and Adventures with Wolf-Birds pp 119-120. New York: Cliff Street Books. ISBN 978-0-06-093063-9
  43. ^ Savage p35
  44. ^ (German) Gwinner, Eberhard (April 1965). "Beobachtungen über Nestbau und Brutpflege des Kolkraben (Corvus corax L.) in Gefangenschaft". Journal of Ornithology 106 (2): 145-178. DOI:10.1007/BF01793758. 
  45. ^ Goodwin. p141
  46. ^ Goodwin. p142
  47. ^ a b c
  48. ^ Heinrich, Bernd (1995). "An Experimental Investigation of Insight in Common Ravens (Corvus Corax)". The Auk 112 (4): 994-1003. Retrieved on 2007-05-16. 
  49. ^ Rozell, Ned. The Raven's Game of Hide and Seek. Alaska Science Forum. Geophysical Institute, University of Alaska Fairbanks. Retrieved on 2007-05-07.
  50. ^ Marzluff and Angell p230
  51. ^ Marzluff and Angell p232
  52. ^ Kijne M & Kotrschal K (2002) "Neophobia affects choice of food-item size in group-foraging common ravens (Corvus corax)". Acta ethologica 5(1): 13-18
  53. ^ Savage pp70 - 71
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Cited texts

  • Goodwin D. (1983). Crows of the World. Queensland University Press, St Lucia, Qld. ISBN 0-7022-1015-3. 
  • John M. Marzluff; Tony Angell (2005). In the Company of Crows and Ravens. ISBN 0-300-10076-0. 
  • Savage, Candace (1995). Bird Brains: The Intelligence of Crows, Ravens, Magpies and Jays. ISBN 1-55054-189-7. 

Further reading

  • Heinrich, B. (1999). Mind of the Raven: Investigations and Adventures with Wolf-Birds. New York: Cliff Street Books. ISBN 978-0-06-093063-9

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