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Corvidae
Common Raven Corvus corax
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Subclass: Neornithes Infraclass: Neoaves Order: Passeriformes Infraorder: Corvida Superfamily: Corvoidea Family: Corvidae Vigors, 1825
Genera
Aphelocoma Calocitta Cissa Corvus Crypsirina Cyanocitta Cyanocorax Cyanolyca Cyanopica Dendrocitta Garrulus Gymnorhinus Nucifraga Perisoreus Pica Platysmurus Podoces Pyrrhocorax Ptilostomus Temnurus Urocissa Zavattariornis and see text

Corvidae is a family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies and nutcrackers^[1]. Collectively its members are called corvids and there are over 120 species. The genus Corvus, including the crows and ravens, makes up over a third of the entire family.

They are medium to large birds with strong feet and bills, rictal bristles and a single moult each year (most passerines moult twice).

Corvids are found worldwide except for the tip of South America and the polar ice caps^[2]. Recently the Corvus genus has re-entered Australia, resulting in five new species and one new subspecies (see crows). The majority of the species are found in tropical South and Central America, southern Asia and Eurasia, with fewer than 10 species each in Africa, Australasia and North America.

Contents 1 Appearance 2 Systematics, taxonomy and evolution 2.1 Fossil record 3 Ecology 3.1 Food and feeding 3.2 Reproduction 3.3 Status and conservation 4 Corvid social life and intelligence 4.1 Corvid intelligence 5 In human myth and culture 6 Footnotes 7 Citations 8 External links

Corvids have feathered, rounded nostrils and strong tails and wings. Many corvids of temperate zones are mainly black or blue; however, some are pied black and white, some have a blue-purple iridescence and many tropical species are highly coloured. The sexes are very similar in color and size. Corvids have strong, stout bills and large wingspans. The larger species are the largest members of the passerine order.

The smallest corvid is the Dwarf Jay (Aphelocoma nana), at 40 g (1.4 oz) and 21.5 cm (8.5 inches). The largest corvids are the Common Raven (Corvus corax) and the Thick-billed Raven (Corvus crassirostris), both of which regularly exceed 1400 grams (3 lbs) and 65 cm (26 inches).

Species can be identified based on size, shape, and geography; however, some, especially the Australian crows, are best identified by their raucous calls.^[3]

The earliest corvid fossils date to the mid-Miocene, about 17 million years ago; Miocorvus and Miopica may be ancestral crows and some magpie lineage, respectively, or similar to the living forms due to convergent evolution.

Over the years there has been much disagreement on the exact evolutionary relationships of the corvid family and their relatives. What eventually seemed clear was that corvids are derived from Australasian ancestors and from there spread throughout the world. Other lineages derived from these ancestors evolved into ecologically diverse, but often Australasian groups. Sibley and Ahlquist united the corvids with other taxa in the Corvida. The presumed corvid relatives included currawongs, birds of paradise, whipbirds, quail-thrushes, whistlers, monarch flycatchers and drongos, shrikes, vireos and vangas^[3], but current research favors the theory that this grouping is partly artificial. The corvids do consitute the core groups of the Corvoidea together with their closest relatives - apparently birds of paradise, Australian mud-nesters and shrikes - and of the Corvida which should only include the Corvoidea and truly related groups such as orioles and vireos.^[4]

Clarification of the interrelationships of the corvids has been achieved based on based on cladistic analysis of several DNA sequences^[5]. The jays and magpies do not constitute monophyletic lineages, but rather seem to split up into an American and Old World lineage, and an Holarctic and Oriental lineage, respectively. These are not closely related among each other. The position of the Azure-winged Magpie, which has always been a major enigma, is even more unclear than it was before.

• Choughs
  • Pyrrhocorax (2 species)
• Treepies
  • Dendrocitta (7 species)
  • Crypsirina (2 species)
  • Temnurus - Ratchet-tailed Treepie
  • Platysmurus - Black Magpie
• Oriental magpies
  • Urocissa (5 species)
  • Cissa (3 species)
• Old World jays and ground jays
  • Garrulus (3 species)
  • Podoces (4 species)
  • Ptilostomus - Piapiac
• Stresemann's Bush Crow, Zavattariornis stresemanni
• Nutcrackers
  • Nucifraga (1-3 species)
• Holarctic magpies
  • Pica (1-6 species)
• Crows, ravens and jackdaws
  • Corvus (some 43-45 species, 1 possibly recently extinct, 1 extinct in the wild)
• Azure-winged Magpie, Cyanopica cyana (possibly 2 species)
• Grey jays
  • Perisoreus (3 species)
• New World jays
  • Aphelocoma - scrub-jays (5-6 species)
  • Calocitta - magpie-jays (2 species)
  • Cyanocitta (2 species)
  • Cyanocorax (17 species)
  • Cyanolyca (9 species, tentatively placed here)
  • Gymnorhinus - Pinyon Jay

The Crested Jay (Platylophus galericulatus) is traditionally included in the Corvidae, but might not to be a member of this family; it is best considered Corvoidea incertae sedis for the time being^{[citation needed]}. Likewise, the Hume's Ground "Jay" (Pseudopodoces humilis) is in fact a member of the titmouse family (Paridae)^[6].

Prehistoric corvid genera are probably mainly of the New World and Old World jays and Holarctic magpies lineages:

• Miocorvus (Middle Miocene of Sansan, France)
• Miopica (Middle Miocene of SW Ukraine)
• Miocitta (Pawnee Creek Late Miocene of Logan County, USA)
• Corvidae gen. et sp. indet. (Edson Early Pliocene of Sherman County, USA)^[7]
• Henocitta (Arredondo Early Pleistocene of Williston, USA)
• Protocitta (Early Pleistocene of Reddick, USA)
• Corvidae gen. et sp. indet. (Early/Middle Pleistocene of Sicily) - probably belongs into extant genus

In addition, there are numerous fossil species of extant genera since the Mio-Pliocene, mainly European Corvus. See the genus accounts for more.

Corvids occur in most climatic zones. Most are sedentary and do not migrate significantly. However, during a shortage of food, eruptive migration can occur^[3]. When species are migratory, they will form large flocks in the fall (around August in the northern hemisphere) and travel south^[8].

One reason for the success of crows, compared to ravens, is their ability to overlap breeding territory. During breeding season, crows were shown to overlap breeding territory six times the overlap of ravens. This invasion of breeding ranges allowed a related increase in local density.^[9]

The natural diet of many corvid species is omnivorous, consisting of invertebrates, nestlings, small mammals, berries, fruits, seeds, and carrion. However, some corvids, especially the crows, have adapted well to human conditions and have come to rely on anthropogenic foods. In a US study of American Crows, Common Ravens and Steller's Jays around campgrounds and human settlements, the crows appeared to have the most diverse diet of all, taking anthropogenic foods such as bread, spaghetti, fried potatoes, dog food, sandwiches, and livestock feed. The increase in available anthropogenic food sources is contributing to population increase in some corvid species.^[9].

Some corvids are predators of other birds. During the wintering months, corvids typically form foraging flocks^[3]. However, some crows also eat many agricultural pests including cutworms, wireworms, grasshoppers and harmful weeds^[8] Some corvid will eat carrion, and since they lack a specialized beak for tearing into flesh, they must wait until animals are opened by other predators or as roadkill.

Since crows do not seem to mind human development, it was suggested that the crow population increase would cause increased rates of nest predation. However, Steller's Jays, which are successful independent of human development, are more efficient in plundering small birds' nests than American Crows and Common Ravens. Therefore, the human relationship with crows and ravens did not increase nest predation by much, especially compared to other factors such as habitat destruction.^[9]

Some corvids are well known communal roosters. Some groups of roosting corvids have been as large as 2,000 birds (Everding and Jones 2006). The partner bond in corvids is extremely strong and even lifelong in some species. This monogamous lifestyle, however, can still contain extra pair copulations. Males and females build large nests together in trees or on ledges. The male will also feed the female during incubation^[10]. The nests are constructed of a mass of bulky twigs lined with grass and bark. Corvids can lay between 3 and 10 eggs, typically ranging between 4 and 7. The eggs are usually greenish in colour with brown blotches. Once hatched, the young remain in the nests for up to 6-10 weeks depending on the species. As expected, corvids provide biparental care.

Jackdaws can breed in buildings or in rabbit warrens^[11]. White-throated Magpie-jays are cooperatively breeding corvids where the helpers are mostly female. Cooperative breeding takes place when additional adults help raise the nestlings. Such helpers at the nest in most cooperatively breeding birds are males, while females join other groups^[12].

Unlike most other species, corvid fitness and reproduction, especially with many crows, has increased due to human development. The survival and reproductive success of certain crows and ravens is assisted by their close relationship with humans.^[9]

Human development provides additional resources by clearing land, creating shrublands rich in berries and insects. When the cleared land naturally replenishes, the young dense trees are used by jays and crows for nesting sites. Ravens typically use larger trees in denser forests.^[9]

Despite the fact that most corvids are not threatened (many even increasing due to human activity) a few species are in danger. For example, the destruction of the Southeast Asian rainforests is endangering mixed-species feeding flocks with members from the family Corvidae^[13]. Also, since its semiarid scrubland habitat is an endangered ecosystem, the Florida Scrub-jay has a small and declining population^[14]. A number of island species have been driven to extinction (like the New Zealand Raven) or are threatened by introduced species (like the Mariana Crow).

In the USA the American Crow population has definitely grown over the years. It is possible, that the American Crow, due to humans increasing suitable habitat, will drive out Northwestern and Fish Crows.^[15]

Some corvids have strong organization and community groups. Jackdaws, for example, have a strong social hierarchy, and are facultatively colonial during breeding^[11]. Providing mutual aid has also been recorded within many of the corvid species.

Young corvids have been known to play and take part in elaborate social games. Documented group games follow a "king of the mountain"- and "follow the leader"-type pattern. Other play involve the manipulation, passing, and balancing of sticks. Corvids also take part in other activities, such as sliding down smooth surfaces. These games are understood to play a large role in the adaptive and survival ability of the birds.^[16]

Mate selection is also quite complex and accompanied with much social play in the Corvidae. Youngsters of social corvids undergo a series of tests, including aerobatic feats, before being accepted as a mate by the opposite sex.^[8]

Some corvids can be aggressive. Blue Jays, for example, are well known to attack anything that threatens their nest. Crows have been known to attack dogs, cats, ravens, and birds of prey. Most of the time these assaults take place as a distraction long enough to allow for an opportunity of stealing food.^[8]

See also: Avian intelligence

Based on the brain-to-body ratio of animals over 1 kilogram, corvid brains are among the largest in birds, equal to that of great apes and cetaceans, and only slightly lower than a human.^[17] Their intelligence is boosted by the long growing up period of the young. By remaining with the parents, the young have more opportunities to learn necessary skills. Since most corvids are cooperative brooders, their young can learn from different members of the group.^[2]

When compared to dogs and cats in an experiment testing the ability to seek out food according to three-dimensional clues, corvid birds did better than the mammals.^[18] A metaanalysis testing how often birds invented new ways to acquire food in the wild found corvids the most innovative birds.^[19] An 2004 study^{[citation needed]} suggests their cognitive abilities are on par with those of great apes. While the avian brain is structured different to the mammalian one, corvids and great apes both evolved the ability to make geometrical measurements. Some Corvids demonstrate the capacity for imagination, something that only humans were thought to possess. For example, they remember the previous relevant social context, use their own experience of having been a thief to predict the behavior of a pilferer, and determined the safest course to protect the caches from pilferage. Studies to assess like cognitive abilities in apes have been inconclusive.^[20]

Corvid ingenuity is represented through their feeding skills, memorization abilities, use of tools, and group behaviour. Living in large social groups has long been connected with high cognitive ability. To live in a large group, a member must be able to recognize individuals and track the social position and foraging of other members over time. Members must also be able to distinguish between sex, age, reproductive status, dominance, and be able to update the information constantly. Therefore, social complexity directly corresponds to high cognition.^[21]

There are also specific examples of corvid cleverness. One Carrion Crow was documented to crack nuts by placing them on a crosswalk, letting the passing cars crack the shell, waiting for the light to turn red, and then safely retrieving the contents.[1]^{[verification needed]} A group of crows in England took turns lifting garbage bin lids while their companions collected food.^{[citation needed]}

Members of the corvid family have been known to watch other birds, remember where they hide their food, then return once the owner leaves. Corvids also move their food around between hiding places to avoid thievery, but only if they have previously been thieves themselves. The ability to hide food requires highly accurate spatial memories. Corvids have been recorded to recall their food's hiding place up to nine months later. It is suggested that vertical landmarks (like trees) are used to remember locations. There has also been evidence that Western Scrub-Jays, which store perishable foods, not only remember where they stored their food, but for how long. This is compared to human episodic memory, which was previously thought unique to humans.^[2]

Looking at the act of thievery in the corvid family, it has been found that some species will take their experience as a thief and use it to predict other bird actions of thievery. This explains why, if a corvid has committed thievery, they will take extra precautions (such as moving hiding places) to avoid being a future victim. Being able to predict others' behaviour based on one's own experiences is another trait previously thought unique to humans. Laboratory experiments have confirmed that crows in particular can sometimes use a past experience to approach a new obstacle.^[2]

New Caledonian Crows (Corvus moneduloides) are famous for their highly developed tool fabrication. They make angling tools of twigs and leavs trimmed into hooks. They then use the hooks to pull insect larvae from tree holes. Tools are engineered according to task and apparently also to learned preference. Other corvids that have been observed using tools include the American Crow, Blue Jay and Green Jay. Diversity in tool design among corvids suggest cultural variation. Again, great apes are the only other non-human animals known to use tools in such a fashion.^[2]

Clark's Nutcrackers and Jackdaws were compared in a 2002 study based on geometric rule learning. The corvids, along with a domestic pigeon, had to locate a target between two landmarks, while distances and landmarks were altered. The nutcrackers were more accurate in their searches than the jackdaws and pigeons.^[22]

An archetypical scare tactic in the agricultural business is the scarecrow. However, due to the corvids quick wit, scarecrows are actually soon ignored and used as perches. Despite farmers' efforts to rid themselves of corvid pests, their attempts have only expanded corvid territories and strengthened their numbers.^[8]

Current systematics places corvids, based on their evolutionary characters, in the lower middle of the passerines, contrary to earlier teleological classifications as "highest" songbirds due to their intelligence.^[4] As per one observer,

"During the 19th century there arose the belief that these were the 'most advanced' birds, based upon the belief that Darwinian evolution brings 'progress.' In such a classification the 'most intelligent' of birds were listed last reflecting their position 'atop the pyramid.' Modern biologists reject the concept of hierarchical 'progress' in evolution [...]."^[3]

The other major group of highly intelligent birds, parrots and cockatoos, is not closely related to corvids either.

Please help improve this article by expanding this section. See talk page for details. Please remove this message once the section has been expanded.

See also: Cultural depictions of ravens and Raven in mythology

Folklore often represents corvids as a clever and even mystical animal. Some^[Who?] Native Americans believed that a raven created the earth and despite being a trickster spirit, ravens were popular on totems, were credited with creating man and were responsible for placing the Sun in the sky. Many Germanic peoples highly revered the raven. The major deity Odin was so associated with ravens throughout history that he gained the kenning "raven god"^[23] and the raven banner was the flag of numerous Germanic tribes^[Who?]. The 6th century BC Greek scribe Aesop featured corvids as intelligent antagonists in many fables. Later, in western literature, popularized by American poet Edgar Allan Poe's work "The Raven," the Common Raven becomes a symbol of the main character's descent into madness.

• Berg, Elena C. (2005): Parentage and reproductive success in the white-throated magpie-jay, Calocitta formosa, a cooperative breeder with female helpers. Animal Behaviour 70(2): 375-385. doi:10.1016/j.anbehav.2004.11.008 (HTML abstract)
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• Corvidae videos on the Internet Bird Collection
• corvids.de - Corvids-Literature-Database
• Corvidae sounds on xeno-canto.org