Corvidae - WikiHQ

Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers. The raven is the largest passerine bird.

Corvids display remarkable intelligence for animals of their size, and are among the most intelligent birds thus far studied. Specifically, members of the family have demonstrated self-awareness in mirror tests (Eurasian magpies) and tool-making ability (e.g. crows and rooks), skills which until recently were thought to be possessed only by humans and a few other mammals. Their total brain-to-body mass ratio is equal to that of non-human great apes and cetaceans, and only slightly lower than that of humans.

They are medium to large in size, with strong feet and bills, rictal bristles, and a single moult each year. Corvids are found worldwide, except for the southern tip of South America and the polar ice caps. Over the years, much disagreement has arisen 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 spread throughout the world from there. Other lineages derived from these ancestors evolved into ecologically diverse, but often Australasian, groups. In the late 1970s and throughout the 1980s, Sibley and Ahlquist united the corvids with other taxa in the Corvida, based on DNA–DNA hybridisation. The presumed corvid relatives included currawongs, birds of paradise, whipbirds, quail-thrushes, whistlers, monarch flycatchers and drongos, shrikes, vireos, and vangas,

Fossil record

The earliest corvid fossils date to mid-Miocene Europe, about 17 million years ago; Miocorvus and Miopica may be ancestral to crows and some of the magpie lineage, respectively, or similar to the living forms, due to convergent evolution. The known prehistoric corvid genera appear to be mainly of the New World and Old World jay and Holarctic magpie lineages:

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)
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 Mio–Pliocene, mainly European Corvus.

Morphology

thumb|upright|Skeleton of ([[American crow|Corvus brachyrhynchos) at the Museum of Osteology ]]

Corvids are large to very large passerines with a robust build and strong legs; all species, except the pinyon jay, have nostrils covered by bristle-like feathers.

Behaviour

Some corvids have strong organisation and community groups. Jackdaws, for example, have a strong social hierarchy and are facultatively colonial during breeding. Some corvids will eat carrion, and since they lack a specialised beak for tearing through tough skin, they must wait until animals are opened, whether by other predators or as roadkill.

Reproduction

thumb|left|A [[Canada jay pair feeding their chicks. ]]

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. 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. Cooperative breeding takes place when parents are helped in raising their offspring, usually by relatives, but also sometimes by non-related adults. Such helpers at the nest in most cooperatively-breeding birds are males, while females join other groups. White-throated magpie-jays are cooperatively-breeding corvids where the helpers are mostly female.

Intelligence

Jerison (1973) has suggested that the degree of brain encephalisation (the ratio of brain size to body size, EQ) may correlate with an animal's intelligence and cognitive skills. Corvids and psittacids have higher EQ than other bird families, similar to that of the apes. Among the Corvidae, ravens possess the largest brain-to-body size ratio. In addition to the high EQ, the Corvid's intelligence is boosted by their living environment. Firstly, Corvids are found in some of the harshest environments on Earth, where surviving requires higher intelligence and better adaptations. Secondly, most Corvids are omnivorous, suggesting they are exposed to a wider variety of stimuli and environments. Furthermore, many corvid species live in large family groups and demonstrate high social complexities.

Their intelligence is boosted by the long growing period of the young. By remaining with the parents, the young have more opportunities to learn necessary skills.

When compared to dogs and cats in an experiment testing the ability to seek out food according to three-dimensional clues, corvids outperformed the mammals. A 2004 review suggested that their cognitive abilities are on par with those of non-human great apes. Most of the time, bystanders already sharing a valuable relationship with the victim are more likely to affiliate with the victim to alleviate the victim's distress ("consolation") as a representation of empathy. Ravens are believed to be sensitive to others' emotions.

Empathy-emotional contagion

Emotion contagion refers to the emotional state matching between individuals. Adriaense et al. (2018) used a bias paradigm to quantify emotional valence, which, along with emotional arousal, defines emotions. They manipulated the positive and negative affective states in the demonstrator ravens, which showed significantly different responses to the two states: behaving pessimism to the negative states, and optimism to the positive states. Then, the researchers trained another observer raven to first observe the demonstrator's responses. The observer raven was then presented with ambiguous stimuli. The experiment results confirmed the existence of negative emotional contagion in ravens, while the positive emotional contagion remained unclear. Therefore, ravens are capable of both discerning the negative emotions in their conspecifics and showing signs of empathy.

Interspecific communications

Interspecific communication is 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. Researchers also examined the avian species' capabilities to interpret this non-verbal communication, and their extent of sensitivity to human emotions. Based on the experimental subject of American Crows' behavioural changes to varying human gazes and facial expressions, Clucas et al. (2013) identified that crows are able to change their behaviour in the presence of direct human gaze, but did not respond differentially to human emotional facial expressions. They further suggested that the high intelligence of the crows enables them to adapt well to human-dominated environments.

Personality conformity

It is considered difficult to study emotions in animals when humans cannot communicate with them. One way to identify animal personality traits is to observe the consistency of the individual's behaviour over time and circumstances. For group-living species, there are two opposing hypotheses regarding the assortment of personalities within a group: the social niche specialisation hypothesis and the conformity hypothesis. To test these two hypotheses, McCune et al. (2018) performed an experiment on the boldness of two species in Corvidae, the Mexican jay and California scrub-jay. Their results confirmed the conformity hypothesis, supported by the significant differences in the group effects.

The individual personality is both determined by genetics and shaped by social contexts. Miller et al. (2016) examined the role of the developmental and social environment in personality formation in common ravens and carrion crows, which are highly social corvids. The researchers highlighted the correlation between social contexts and an individual's consistent behaviour over time (personality) by showing that conspecific presence promoted the behavioural similarities between individuals. Therefore, the researchers demonstrated that social contexts had a significant impact on the development of the raven's and crow's personalities.

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, memorisation 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 recognise 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. but later research could not replicate this finding. Studies using very similar setups could not find such behaviour in other corvids (e.g., Carrion crows). Magpies have been observed taking part in elaborate grieving rituals, which have been likened to human funerals, including laying grass wreaths. Marc Bekoff, at the University of Colorado, argues that it shows that they are capable of feeling complex emotions, including grief. A related study shows that the birds' pallium's neuroarchitecture is reminiscent of the mammalian cortex.

Tool use, memory, and complex rational thought

thumb|A [[New Caledonian crow uses a tool to retrieve the correct tool to obtain food.]]

There are also specific examples of corvid intelligence. 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. A group of crows in England took turns lifting garbage bin lids while their companions collected food.

Members of the corvid family have been known to watch other birds, remember where they hide their food, and 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; they remember previous relevant social contexts, use their own experience of having been a thief to predict the behaviour of a pilferer, and can determine the safest course to protect their caches from being pilfered. Studies to assess similar cognitive abilities in apes have been inconclusive.

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 also for how long. This has been compared to episodic memory, previously thought to be unique to humans. Other corvids that have been observed using tools include: the American crow, blue jay, and green jay. Researchers have discovered that New Caledonian crows do not just use single objects as tools—they can also construct novel compound tools through the assemblage of otherwise non-functional elements. Diversity in tool design among corvids suggests cultural variation. Again, great apes are the only other animals known to use tools in such a fashion.

Disease

Corvids are reservoirs (carriers) for the West Nile virus in the United States. They are infected by mosquitoes (the vectors), primarily of the Culex species. Crows and ravens 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 ravens, have occasionally served as pets, although they are not able to speak as readily as parrots, 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 ravens (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, believed that a raven created the earth, and despite being a trickster spirit, ravens were popular on totems, credited with creating man, and considered responsible for placing the Sun in the sky.

Due to their carrion diet, the Celtic 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"), both who were underworld deities that may be related to the later Arthurian Fisher King. The Welsh Dream of Rhonabwy illustrates well the association of ravens with war. In many parts of Britain, gatherings of crows, or more often magpies, are counted using the divination rhyme: "one for sorrow, two for joy, three for a girl, four for a boy, five for silver, six for gold, seven for a secret never to be told." Another rhyme is: "one for sorrow, two for mirth, three for a funeral, four for a birth, five for heaven, six for hell, and seven for the Devil, his own sel." Cornish superstition holds that when a lone magpie is encountered, it must be loudly greeted with respect.

Various Germanic peoples highly revered the raven, and the raven was often depicted as a motif on shields or other war implements 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 Scandinavian chieftains. Odin was also attended by Hugin and Munin, two ravens who flew all over the world, and whispered information they acquired into his ears.

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 fish crows to decline.

External links

Corvidae videos on the Internet Bird Collection
corvids.de – Corvids-Literature-Database
Corvid Corner A site about the Corvidae
AvesNoir A site about corvids in art, culture, and literature.
Discovery of species-wide tool use in the Hawaiian crow
Rooks reveal remarkable tool use
Clever New Caledonian crows can use three tools
Talking Eurasian magpie Pica pica
Rare crow shows a talent for tool use