Corvidae is a cosmopolitan family of Songbird passerine that contains the , , rooks, , , , , , and nutcrackers.[ In Colloquialism English, they are known as the crow family or corvids. Currently, 139 species are included in this family. The genus Corvus containing 50 species makes up over a third of the entire family.]
Corvids display remarkable Animal cognition for animals of their size, and are among the most intelligent birds thus far studied.[Birding in India and South Asia: Corvidae. Retrieved 2007-Nov-10]
They are medium to large in size, with strong feet and bills, rictal bristles, and a single Moulting each year (most passerines moult twice). Corvids are found worldwide, except for the southern tip of South America and the polar .[ The majority of the species are found in tropical South and Central America and in southern Asia, with fewer than 10 species each in Africa and Australasia. The genus Corvus has re-entered Australia in relatively recent geological prehistory, with five species and one subspecies there. Several species of raven have reached oceanic islands, and some of these species are now highly threatened with extinction, or have already become extinct.
]
Systematics, taxonomy, and evolution
The name Corvidae for the family was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820.[ The name of the author is not specified in the document.][ but current research favors the theory that this grouping is partly artificial. The corvids constitute the core group of the Corvoidea, together with their closest relatives (the birds of paradise, Australian mud-nesters, and shrikes). They are also the core group of the Corvida, which includes the related groups, such as Old World orioles and vireos.][
]
Clarification of the interrelationships of the corvids has been achieved based on cladistic analysis of several .[ The jays and magpies do not constitute monophyletic lineages, but rather seem to split up into an Americas 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 of undistinguished lineage, is less clear than previously thought.
]
The crested jayshrike ( Platylophus galericulatus) is traditionally included in the Corvidae, but is not a true member of this family, being closer to the Prionops (Malaconotidae) or (Laniidae).[ Likewise, the Hume's ground "jay" ( Pseudopodoces humilis) is, in fact, a member of the tit family, Paridae.][ The following tree showing the phylogeny of the crow family is based on a molecular study by Jenna McCullough and collaborators published in 2023.]
Fossil record
The earliest corvid date to mid-Miocene Europe,
-
Miocorvus (Middle Miocene of Sansan, Gers in southwestern France)
-
Miopica (Middle Miocene of SW Ukraine)
-
Miocitta (Pawnee Creek Late Miocene of Logan County, US)
-
Corvidae gen. et sp. indet. (Edson Early Pliocene of Sherman County, Kansas, US)
[Proximal right coracoid of a jay-sized bird, perhaps an Holarctic magpie distinct from Pica: ]
-
Protocitta (Early Pleistocene of Reddick, US)
-
Corvidae gen. et sp. indet. (Early/Middle Pleistocene of Sicily) – probably belongs in an extant genus
-
Henocitta (Arredondo Clay Middle Pleistocene of Williston, US)
In addition, there are numerous fossil species of extant genera since the Miocene–Pliocene, mainly European Corvus.
Morphology
Corvids are large to very large with a robust build and strong legs; all species, except the pinyon jay, have covered by bristle-like feathers.[ Many corvids of temperate zones have mainly black or blue coloured plumage; however, some are pied black and white, some have a blue-purple iridescence, and many tropical species are brightly coloured. The sexes are very similar in color and size. Corvids have strong, stout bills and large wingspans. The family includes the largest members of the passerine order.
]
The smallest corvid is the dwarf jay ( Cyanolyca nanus), at and . The largest corvids are the common raven ( Corvus corax) and the thick-billed raven ( Corvus crassirostris), both of which regularly exceed and .
Species can be identified based on size, shape, and geography; however, some, especially the , are best identified by their raucous calls.
Ecology
Corvids occur in most climatic zones. Most are sedentary, and do not bird migration significantly. However, during a shortage of food, irruptive migration can occur.
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 as much as ravens. This invasion of breeding ranges allowed a related increase in local population density.
Since crows and magpies have benefited and even increased in numbers due to human development, it was suggested that this might cause increased rates of nest predation of smaller bird species, leading to declines. Several studies have shown this concern to be unfounded. One study examined , which had increased in numbers, were a suspect in nest predation of threatened . However, Steller's jays, which are successful independently of human development, are more efficient in plundering small birds' nests than and . Therefore, the human relationship with crows and ravens did not significantly increase nest predation when compared to other factors, such as habitat destruction.
Behaviour
Some corvids have strong organization and community groups. Jackdaws, for example, have a strong social hierarchy, and are facultatively colonial during breeding.[ 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 . Documented group games follow "king of the mountain" or "follow the leader" patterns. Other play involves 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.[
]
Mate selection is quite complex, and accompanied with much social play in the Corvidae. Youngsters of social corvid species undergo a series of tests, including aerobatic feats, before being accepted as a mate by the opposite sex.
Some corvids can be aggressive. , 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 an opportunity for stealing food.
Food and feeding
The natural diet of many corvid species is omnivorous, consisting of , 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 human food sources. In a US study of , , 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 human food sources is contributing to population rises in some corvid species.[
]
Some corvids are predators of other birds. During the wintering months, corvids typically form foraging flocks.[Shades of Night: The Aviary . Version of 2004-JUL-21. Retrieved 2007-NOV-10.] Some corvids will eat carrion, and since they lack a specialized beak for tearing into flesh, they must wait until animals are opened, whether by other predators or as roadkill.
Reproduction
Many species of corvid are territorial, protecting territories throughout the year, or simply during the breeding season. In some cases, territories may only be guarded during the day, with the pair joining off-territory roosts at night. Some corvids are well-known communal roosters. Some groups of roosting corvids can be very large, with a roost of 65,000 rooks counted in Scotland.[ Some, including the rook and the jackdaw, are also communal nesters.
]
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; jackdaws are known to breed in buildings and in rabbit warrens.][Encyclopædia Britannica Online: Corvidae. Free subscription required.] 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.
Corvids use several different forms of parental care, including bi-parental care and cooperative breeding.
Intelligence
Jerison (1973) has suggested that the degree of brain encephalization (the ratio of brain size to body size, EQ) may correlate with an animal's intelligence and cognitive skills.
Their intelligence is boosted by the long growing period of the young.
When compared to dogs and cats in an experiment testing the ability to seek out food according to three-dimensional clues, corvids out-performed the mammals.[ A meta-analysis testing how often birds invented new ways to acquire food in the wild found corvids to be the most innovative birds.][Rincon, Paul (22 February 2005) Crows and jays top bird IQ scale. BBC.] A 2004 review suggested that their cognitive abilities are on par with those of non-human great apes.[ Despite structural differences, the brains of corvids and great apes both evolved the ability to make geometrical measurements.
]
Empathy-consolation
Ravens are found to show bystander affiliation, and solicited bystander affiliation after aggressive conflicts.
Empathy-emotional contagion
Emotion contagion refers to the emotional state matching between individuals. Adriaense et al. (2018) used a cognitive bias paradigm to quantify emotional valence, which along with emotional arousal, define emotions.
Interspecific communications
Interspecific communications are evolutionarily beneficial for species living in the same environment. Facial expressions are the most widely used method to express emotions by humans. Tate et al. (2006) explored the issue of non-human mammals processing the visual cues from faces to achieve interspecific communication with humans.
Personality conformity
It is considered difficult to study emotions in animals when humans could not communicate with them. One way to identify animal personality traits is to observe the consistency of the individual's behavior over time and circumstances.
Social construction
The individual personality is both determined by genetics and shaped by .
Social complexity
The social complexity hypothesis suggests that living in a social group enhances the cognitive abilities of animals. 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, and dominance, and to update this information constantly. It might be that social complexity corresponds to their high cognition, as well as contributing to the spread of information between members of the group.
Consciousness, culture-rudiments, and neurology
A study published in 2008 suggested that the Eurasian magpie is the only non-mammal species known to be able to recognize itself in a mirror test,[ Animal emotions, wild justice and why they matter: Grieving magpies, a pissy baboon, and empathic elephants Emotion, Space and Society xxx (2009) 1–4, Marc Bekoff] Marc Bekoff, at the University of Colorado, argues that it shows that they are capable of feeling complex emotions, including grief.
Tool use, memory, and complex rational thought
There are also specific examples of corvid cleverness. One carrion crow was documented cracking 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.
Members of the corvid family have been known to watch other birds, remember where they hide their food, then return once the owner leaves.[Owen, James (9 December 2004) Crows as Clever as Great Apes, Study Says. National Geographic News, Retrieved 2007-NOV-10.]
The ability to hide food requires highly accurate spatial memories. Corvids have been recorded to recall their food's hiding places up to nine months later. It is suggested that vertical landmarks (like trees) are used to remember locations. There has also been evidence that California scrub jays, which store perishable foods, not only remember where they stored their food, but for how long. This has been compared to episodic memory, previously thought unique to humans.
New Caledonian crows ( Corvus moneduloides) are notable for their highly developed tool fabrication. They make angling tools of twigs and leaves trimmed into hooks, and then subsequently use the hooks to pull insect larvae from tree holes. Tools are engineered according to task, and apparently, also to learned preferences. Recent studies revealed abilities to solve complicated problems, which suggested high levels of innovation of a complex nature.
Clark's nutcrackers and 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.[
]
Implications and specific comparisons with other animals
The scarecrow is an archetypal scare tactic in the agricultural business. However, due to corvids' quick wit, scarecrows are 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.
Contrary to earlier teleological classifications, in which they were seen as "highest" songbirds due to their intelligence, current systematics might place corvids—based on their total number of physical characteristics, instead of just their brains (which are the most developed of birds)—in the lower middle of the passerine evolutionary tree, dependent on which subgroup is chosen as the most derived.
The other major group of highly intelligent birds of the order Psittaciformes (which includes Psittacidae, , and New Zealand parrots) is not closely related to corvids.
A study found that four-month-old ravens can have physical and social cognitive skills similar to that of adult great apes, and concluded that the "dynamic of the different influences that, during ontogeny, contributes to adult cognition" is required for the study of cognition.[ Available under CC BY 4.0.]
Disease
Corvids are reservoirs (carriers) for the West Nile virus in the United States. They are infected by mosquitoes (the Disease vector), primarily of the Culex species. and are quickly killed by this disease, so their deaths are an early-warning system when West Nile virus arrives in an area (as are horses and other bird-species deaths). One of the first signs that West Nile virus first arrived in the US in 1999 was the death of crows in New York.
Relationship with humans
Several different corvids, particularly , have occasionally served as pets, although they are not able to speak as readily as , and are not suited to a caged environment.
It is illegal to own corvids, or any other migratory bird, without a permit in the United States, due to the Migratory Bird Act.
Humans have been able to coexist with many members of the Corvidae family throughout history, most notably crows and (see: "Role in myth and culture" section below). These positive interactions have extended into modern times.
Role in myth and culture
Folklore often represents corvids as clever, and even mystical, animals. Some Native Americans, such as the Haida people, believed that a raven created the earth, and despite being a trickster spirit, ravens were popular on , credited with creating man, and considered responsible for placing the Sun in the sky.
Due to their carrion diet, the Celts peoples strongly associated corvids with war, death, and the battlefield; their great intelligence meant that they were often considered messengers, or manifestations of the gods, such as Bendigeidfran (Welsh for "Blessed Crow") or the Irish Morrigan (Middle Irish for "Great Queen"),
Various Germanic peoples highly revered the raven, and the raven was often depicted as a motif on shields or other war gear in Anglo-Saxon art, such as the Sutton Hoo burial, and Vendel period art. The major deity, Odin, was so commonly associated with ravens throughout history that he gained the kenning "Raven God," and the raven banner was the flag of various Viking Age chieftains. Odin was also attended by Hugin and Munin, two Common raven who flew all over the world, and whispered information they acquired into his ears.[ The Valravn sometimes appeared in modern Scandinavian folklore. On a shield and purse lid excavated among the Sutton Hoo treasures, imagery of stylised corvids with scrolled beaks are meticulously detailed in the decorative enamel work. The corvid symbolism reflected their common totemic status to the Anglo-Saxons, whose pre-Christian Woden were of the same origin as that of the aforementioned Vikings.
]
The sixth century BCE Ancient Greece 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.
The children's book Mrs. Frisby and the Rats of NIMH and its animated film adaptation features a protagonist crow named Jeremy.
Status and conservation
Unlike many other bird families, 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.
Human development provides additional resources by clearing land, creating shrublands rich in berries and insects. When the cleared land naturally replenishes, jays and crows use the young dense trees for nesting sites. Ravens typically use larger trees in denser forest.
Most corvids are not threatened, and many species are even increasing in population due to human activity. However, a few species are in danger. For example, the destruction of the Southeast Asian rainforest is endangering mixed-species feeding flocks with members from the family Corvidae.[ Also, since its semiarid scrubland habitat is an endangered ecosystem, the Florida scrub jay has a small and declining population.][ A number of island species, which are more vulnerable to introduced species and habitat loss, have been driven to extinction, such as the New Zealand raven, or are threatened, like the Mariana crow.
]
The American crow population of the United States has grown over the years. It is possible that the American crow, due to humans increasing suitable habitat, will cause Northwestern crows and to decline.[
]
Species
FAMILY CORVIDAE
-
-
-
Oriental
-
Genus Cissa
-
Common green magpie, Cissa chinensis
-
Indochinese green magpie, Cissa hypoleuca
-
Javan green magpie, Cissa thalassina
-
Bornean green magpie, Cissa jefferyi
-
Genus Urocissa
-
Taiwan blue magpie, Urocissa caerulea
-
Red-billed blue magpie, Urocissa erythroryncha
-
Yellow-billed blue magpie, Urocissa flavirostris
-
Sri Lanka blue magpie, Urocissa ornata
-
White-winged magpie, Urocissa whiteheadi
-
Old World and close relatives
-
Genus Garrulus
-
Genus Podoces – ground jays
-
Xinjiang ground jay, Podoces biddulphi
-
Mongolian ground jay, Podoces hendersoni
-
Turkestan ground jay, Podoces panderi
-
Iranian ground jay, Podoces pleskei
-
Genus Ptilostomus
-
Genus Zavattariornis
-
Stresemann's bushcrow, Zavattariornis stresemanni
-
Nutcrackers
-
Genus Nucifraga
-
Northern nutcracker, Nucifraga caryocatactes
-
Southern nutcracker, Nucifraga hemispila
-
Kashmir nutcracker, Nucifraga multipunctata
-
Clark's nutcracker, Nucifraga columbiana
-
Holarctic
-
True crows (, , and rooks)
-
Genus Corvus
-
Australian and Melanesian species
-
Little crow, Corvus bennetti
-
Australian raven, Corvus coronoides
-
Bismarck crow, Corvus insularis
-
Brown-headed crow, Corvus fuscicapillus
-
Bougainville crow, Corvus meeki
-
Little raven, Corvus mellori
-
New Caledonian crow, Corvus moneduloides
-
Torresian crow, Corvus orru
-
Forest raven, Corvus tasmanicus
-
Grey crow, Corvus tristis
-
Long-billed crow, Corvus validus
-
White-billed crow, Corvus woodfordi
-
Pacific island species
-
Alalā (Hawaiian crow), Corvus hawaiiensis (formerly Corvus tropicus) (extinct in the wild)
-
Mariana crow, Corvus kubaryi
-
Tropical Asian species
-
Sunda crow, Corvus enca
-
Sulawesi crow, Corvus celebensis
-
Samar crow, Corvus samarensis
-
Sierra Madre crow, Corvus sierramadrensis
-
Palawan crow, ''Corvus pusillus
-
Flores crow, Corvus florensis
-
Large-billed crow, Corvus macrorhynchos
-
Eastern jungle crow, Corvus levaillantii
-
Indian jungle crow, Corvus culminatus
-
House crow, Corvus splendens
-
Collared crow, Corvus torquatus
-
Piping crow, Corvus typicus
-
Banggai crow, Corvus unicolor
-
Violet crow, Corvus violaceus
-
Eurasian and North African species
-
Hooded crow, Corvus cornix
-
Mesopotamian crow, Corvus (cornix) capellanus
-
Carrion crow, Corvus corone
-
Eastern carrion crow, Corvus (corone) orientalis
-
Rook, Corvus frugilegus
-
Fan-tailed raven, Corvus rhipidurus
-
Brown-necked raven, Corvus ruficollis
-
Holarctic species
-
North and Central American species
-
American crow, Corvus brachyrhynchos
-
Northwestern crow, Corvus brachyrhynchos caurinus
-
Chihuahuan raven, Corvus cryptoleucus
-
Tamaulipas crow, Corvus imparatus
-
Jamaican crow, Corvus jamaicensis
-
White-necked crow, Corvus leucognaphalus
-
Cuban crow, Corvus nasicus
-
Fish crow, Corvus ossifragus
-
Hispaniolan palm crow, Corvus palmarum
-
Cuban palm crow ( Corvus minutus)
-
Sinaloa crow, Corvus sinaloae
-
Western raven, Corvus (corax) sinuatus
-
Tropical African species
-
White-necked raven, Corvus albicollis
-
Pied crow, Corvus albus
-
Cape crow, Corvus capensis
-
Thick-billed raven, Corvus crassirostris
-
Somali crow, Corvus edithae
-
Genus Coloeus
-
Boreal
-
New World
-
Genus Aphelocoma – scrub-jays
-
California scrub jay, Aphelocoma californica
-
Island scrub jay, Aphelocoma insularis
-
Woodhouse's scrub jay, Aphelocoma woodhouseii
-
Florida scrub jay, Aphelocoma coerulescens
-
Mexican jay, Aphelocoma wollweberi
-
Transvolcanic jay, Aphelocoma ultramarina
-
Unicolored jay, Aphelocoma unicolor
-
Genus Cyanocitta
-
Blue jay, Cyanocitta cristata
-
Steller's jay, Cyanocitta stelleri
-
Genus Cyanocorax
-
Black-throated magpie-jay, Cyanocorax colliei
-
White-throated magpie-jay, Cyanocorax formosa
-
Black-chested jay, Cyanocorax affinis
-
Purplish-backed jay, Cyanocorax beecheii
-
Azure jay, Cyanocorax coeruleus
-
Cayenne jay, Cyanocorax cayanus
-
Plush-crested jay, Cyanocorax chrysops
-
Curl-crested jay, Cyanocorax cristatellus
-
Purplish jay, Cyanocorax cyanomelas
-
White-naped jay, Cyanocorax cyanopogon
-
Tufted jay, Cyanocorax dickeyi
-
Azure-naped jay, Cyanocorax heilprini
-
Bushy-crested jay, Cyanocorax melanocyaneus
-
White-tailed jay, Cyanocorax mystacalis
-
San Blas jay, Cyanocorax sanblasianus
-
Violaceous jay, Cyanocorax violaceus
-
Green jay, Cyanocorax luxuosus
-
Inca jay, Cyanocorax yncas
-
Yucatan jay, Cyanocorax yucatanicus
-
Brown jay, Cyanocorax morio
-
Genus Cyanolyca
-
Silvery-throated jay, Cyanolyca argentigula
-
Black-collared jay, Cyanolyca armillata
-
Azure-hooded jay, Cyanolyca cucullata
-
White-throated jay, Cyanolyca mirabilis
-
Dwarf jay, Cyanolyca nanus
-
Beautiful jay, Cyanolyca pulchra
-
Black-throated jay, Cyanolyca pumilo
-
Turquoise jay, Cyanolyca turcosa
-
White-collared jay, Cyanolyca viridicyanus
-
Genus Gymnorhinus
Explanatory notes
Further reading
-
Charles Sibley & Jon Edward Ahlquist (1991): Phylogeny and Classification of Birds: A Study in Molecular Evolution. New Haven, Conn.: Yale University Press. .
External links
