Corvidae

The corvids (Corvidae) are a family of birds in the order Passeriformes. These birds are polyphagous and often scavengers.

Corvids show remarkable intelligence for animals of their size and are among the most intelligent birds studied so far. Specifically, members of the family have demonstrated self-awareness in the mirror test (European magpie) and the ability to make tools (e.g. crows and rooks), abilities that until recently were believed to be possessed only by humans and some other higher mammals. Their brain/total 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 legs and beaks, rictal bristles and only one molt of feathers per year (most passerines molt twice). Corvids are found throughout the world except the southern tip of South America and the polar ice caps. Most species are found in Central America and southern Asia, with fewer than 10 species 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 crows have arrived on oceanic islands, and some of these species are now highly threatened with extinction or have already become extinct.

Morphology

Corvids are large or very large passerines, robustly built, with strong legs and all species, except the pinyon magpie, have their nostrils covered by bristle-like feathers. Many corvids from temperate zones have plumage mainly black or blue; However, some are black and white, others have a blue-purple iridescence, and many tropical species are brightly colored. The sexes are very similar in color and size. Corvids have a strong, robust beak and a large wingspan. The family includes the largest members of the passerine order.

The smallest corvid is the pygmy jay (Cyanolyca nana), at 41 g (1.4 oz) and 21.5 cm (8.5 in). The largest corvids are the common crow (Corvus corax) and the thick-billed crow (Corvus crassirostris), both of which regularly exceed 1,400 grams (3.1 lb) and 65 cm (25.6 in).

Species can be identified based on size, shape and geography; However, some, especially Torres' crows, are best identified by their strident calls.

Ecology

Corvids are present in most climatic zones. Most are sedentary and do not migrate significantly. However, during a food shortage, irruptive migration can occur. When species are migratory, they form large flocks in autumn (around August in the northern hemisphere) and travel south.

One of the reasons for the success of common crows, compared to other species, is their ability to overlap their breeding territory. During the breeding season, common crows were shown to overlap their breeding territory six times more than other crows. This invasion of breeding areas allowed for a related increase in local population density.

As crows and magpies have benefited and even increased in numbers due to human development, it was suggested that this could cause increased nest predation rates of smaller bird species, leading to the reduction. Several studies have shown that this concern is unfounded. One study examined American crows, whose numbers had increased, as suspected predators of threatened marbled murrelet nests. However, the Steller's jay, which is successful regardless of human development, is more effective at raiding the nests of small birds than the American crow and the common crow. Therefore, human involvement with crows and crows did not significantly increase nest predation, compared to other factors such as habitat destruction. Similarly, a study examining the decline of British songbirds found no no relationship between the number of common magpies and changes in the population of 23 species of songbirds.

Behavior

Some corvids have strong organization and community groups. Jackdaws, for example, have a strong social hierarchy and are facultatively colonial during breeding. Mutual aid has also been recorded in many corvid species.

Young corvids are known to play and engage in elaborate social games. Documented group games follow "king of the mountain" or "follow the leader". Other games involve manipulating, passing and balancing sticks. Corvids also engage in other activities, such as sliding on smooth surfaces. It is understood that these games play an important role in the birds' ability to adapt and survive.

Mate selection is quite complex and is accompanied by many social games in corvids. Young social corvid species undergo a series of tests, including acrobatic feats, before being accepted as a mate by the opposite sex.

Some corvids can be aggressive. Blue jays, for example, are known to attack anything that threatens their nest. Crows have been known to attack dogs, cats, crows and birds of prey. Most of the time these attacks take place as a distraction long enough to allow an opportunity to steal food.

Food and nutrition

The natural diet of many corvid species is omnivorous and consists of invertebrates, chicks, small mammals, berries, fruits, seeds and carrion. However, some corvids, especially crows, have adapted well to human conditions and have come to rely on human food sources. In a study conducted in the United States on American crows, common crows, and Steller's jays around camps and human settlements, the crows appeared to have the most diverse diet of all, eating anthropogenic foods such as bread, spaghetti, French fries, food for dogs, sandwiches and livestock feed. The increase in available human food sources is contributing to the population increase of some corvid species.

Some corvids are predators of other birds. During the hibernation months, corvids often form foraging flocks. However, some crows also feed on many agricultural pests, such as cutworms, wireworms, grasshoppers, and noxious weeds. Some corvids feed on carrion, and since they lack a specialized beak to tear flesh, they must wait for the animals to be cut open, either by other predators or as roadkill.

Playback

Many species of corvids are territorial, protecting territories throughout the year or simply during the breeding season. In some cases, territories are only guarded during the day, and the pair join roosts outside the territory at night. Some corvids are well-known communal roosters. Some groups of roosting corvids can be very large, with a roost of 65,000 roosts recorded in Scotland. Some, including the rook and jackdaw, are also communal nesters.

The pair bond in corvids is extremely strong and even lifelong in some species. This monogamous lifestyle, however, may contain extra-pair copulations. Males and females build large nests together in trees or on ledges; Jackdaws are known to breed in buildings and hutches. The male will also feed the female during incubation. Nests are built from a mass of voluminous twigs lined with grass and bark. Corvids can lay between 3 and 10 eggs, usually between 4 and 7. The eggs are usually greenish in color with brown spots. Once hatched, the young remain in the nests for up to 6-10 weeks, depending on the species.

Corvids use different forms of parental care, including biparental care and cooperative breeding. Cooperative breeding occurs when parents receive help in raising their offspring, usually from relatives, but sometimes also from of unrelated adults. Such nest helpers in most cooperatively breeding birds are males, while females join other groups. Beautiful white-throated magpies are cooperatively breeding corvids in which the helpers are mostly female.

Intelligence

Jerison (1973) has suggested that the degree of brain encephalization (the ratio of brain size to body size, EQ) may be correlated with animals' intelligence and cognitive abilities. Corvids and psittacines They have a higher IQ than other bird families, similar to that of apes. While among corvids, crows have the greatest ratio between brain and body size. In addition to the high IQ, the corvid's intelligence is enhanced by its living environment. First, corvids are found in some of the harshest environments on Earth, where survival requires higher intelligence and better adaptations. Second, most corvids are omnivores, suggesting that they are exposed to more different stimuli and environments. Additionally, many species of corvids live in a large family group and demonstrate great social complexity.

Their intelligence is enhanced by the long period of growth of the young. By staying with the parents, the young have more opportunities to learn the necessary skills.

When compared to dogs and cats in an experiment in which the ability to search for food based on three-dimensional cues was tested, corvids outperformed mammals. A meta-analysis in which the frequency with which they birds invented new ways to get food in the wild found that corvids were the most innovative birds. A 2004 review suggests that their cognitive abilities are on par with those of non-human great apes. Despite the differences Structurally, the brains of corvids and great apes both evolved the ability to make geometric measurements.

Empathy-consolation

Crows have been found to show affiliation to bystanders and solicit affiliation from bystanders after aggressive conflicts. Most of the time, bystanders who share a valued relationship with the victim are more likely to affiliate with them to relieve their distress ("consolation") as a representation of empathy. It is believed that crows are capable of being sensitive to the emotions of others.

Empathic-emotional contagion

The contagion of emotions refers to the coincidence of emotional states between individuals. Adriaense et al. (2018) used a cognitive bias paradigm to quantify emotional valence, which along with emotional arousal, define emotions. They manipulated positive and negative affective states in demonstrator crows, which showed significantly different responses to the two states: behaving with pessimism in the face of negative states and with optimism in the face of positive states. Next, the researchers trained another observer crow to first observe the demonstrator's responses and then present it with ambiguous stimuli. The results of the experiment confirmed the existence of negative emotional contagion in crows, while positive emotional contagion remained unclear. Therefore, crows are able to discern negative emotions in their fellow crows and show signs of empathy.

Interspecific communications

Interspecific communication is evolutionarily beneficial for species that live in the same environment. Facial expressions are the ways most used by humans to express emotions. Tate et al.(2006) explored the question of non-human mammals processing visual cues from the face to achieve interspecific communication with humans. The researchers also examined the ability of avian species to interpret this non-verbal communication and be sensitive to human emotions. Based on the experimental topic of behavioral changes of American crows when faced with different human gazes and facial expressions, Clucas et al. (2013) identified that crows are capable of changing their behaviors when faced with human emotions. Furthermore, they suggested that crows' high intelligence allows them to adapt well to human-dominated environments.

Personality conformity

It is considered difficult to study emotions in animals when humans could not communicate with them. One way to identify personality traits in animals is to observe the consistency of the individual's behavior over time and circumstances. In the case of species that live in groups, there are two opposing hypotheses about the variety of behavior. Personality within a group: The social niche specialization hypothesis and the conformity hypothesis. To test these two hypotheses, McCune et al. (2018) conducted an experiment on the boldness of two species of Corvidae: the Mexican Jay and the California Jay. Their results confirmed the conformity hypothesis, supported by significant differences in group effects.

Social construction

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

Social complexity

The social complexity hypothesis is that living in a social group improves the cognitive abilities of animals. The ingenuity of corvids is represented through their feeding skills, memorization, tool use, and group behavior. Living in large social groups has long been linked to high cognitive ability. To live in a large group, a member must be able to recognize individuals and follow 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 update this information constantly. It is possible that social complexity corresponds to their high cognition, in addition to contributing to the dissemination of information among group members.

Consciousness, rudiments of culture and neurology

The Eurasian magpie is the only known non-mammalian species capable of recognizing itself in a mirror test although subsequent research was unable to replicate this finding. Studies using very similar setups failed to find such behavior in other corvids (e.g. carrion crows). Magpies have been observed engaging in elaborate mourning rituals, which have been compared to human funerals, including the laying of grass wreaths. Marc Bekoff of the University of Colorado argues that this shows that they are capable of feeling emotions. complex, including grief. Additionally, carrion crows show a neural response that correlates with their perception of a stimulus, which some scientists have argued is an empirical marker of (avid/corvid) sensory awareness – the conscious perception of sensory input - in crows that do not have a cerebral cortex. A related study shows that the neuroarchitecture of the bird pallium is reminiscent of the cortex of mammals.

Use of tools, memory and complex rational thinking

There are also concrete examples of corvid cunning. A carrion crow has been documented to crack nuts by placing them in a crosswalk, letting passing cars crack the shell, waiting for the traffic light to turn red, and then safely retrieving the contents. A group of crows in England he took turns lifting the lids of garbage containers while his companions collected food.

Members of the corvid family are known to watch other birds, remember where they hide food, and then return once the owner leaves. Corvids also move their food between hiding places to prevent theft., but only if they themselves have previously been thieves (i.e., they remember previous relevant social contexts, use their own experience of having been a thief to predict the behavior of a thief, and can determine the safest path to protect their hiding places from being robbed).). Studies evaluating similar cognitive abilities in apes have been inconclusive.

The ability to hide food requires very precise spatial memory. It has been recorded that corvids remember the location where their food is hidden up to nine months later. It is suggested that vertical landmarks (such as trees) are used to remember locations. It has also been proven that California jays, which store perishable foods, not only remember where they have stored their food, but for how long. This has been compared to episodic memory, which was previously believed to be unique to humans.

New Caledonian crows (Corvus moneduloides) are notable for their highly developed tool making. They make fishing tools from twigs and leaves cut into hooks, which they then use to remove insect larvae from holes in trees. Tools are designed based on the task and, it seems, also on learned preferences. Recent studies have revealed their ability to solve complicated problems, suggesting a high level of innovation of a complex nature. Other corvids that have been observed using tools include the American crow, blue jay, and green jay. Researchers have discovered that New Caledonian crows don't just use individual objects as tools; They can also construct new composite tools by assembling otherwise non-functional elements.

Clark's nutcrackers and rooks were compared in a 2002 study based on learning geometric rules. The corvids, along with a domestic pigeon, had to locate a target between two landmarks, while altering the distances and landmarks. Nutcrackers were more precise in their searches than jackdaws and pigeons.

Specific implications and comparisons with other animals

The scarecrow is an archetypal scare tactic in the agricultural business. However, due to the corvids' quick wit, the scarecrows are soon ignored and used as perches. Despite farmers' efforts to rid themselves of corvid infestations, their attempts have only expanded the corvids' territories and strengthened their numbers.

Contrary to previous teleological classifications in which they were considered "taller" songbirds, Due to their intelligence, current systematics could place corvids, based on their total number of physical characteristics instead of just their brain (which is the most developed of birds), in the lower middle part of the evolutionary tree of the birds. passerines, depending on which subgroup is chosen as the most derived. According to one observer:

During the 19th century the belief that these were the most advanced birds, based on the belief that Darwinian evolution contributes 'progress'. In this classification, "smart" birds appeared in the last place, reflecting their position "on the top of the pyramid". Modern biologists reject the concept of hierarchical "progress" in evolution [...]. !

The other large group of highly intelligent birds in the order Psittaciformes (which includes 'true' parrots, cockatoos, and New Zealand parrots) is not closely related to corvids.

A study found that four-month-old crows may have physical and social cognitive abilities similar to those of adult great apes and concludes that a "dynamics of the different influences that, during ontogeny, are required contributes to adult cognition" for the study of cognition.

Genres

The Corvidae family is currently made up of 25 genera:

• Aphelocoma Cabanis, 1851
• Calocitta Gray, 1841
• Cissa Boie, 1826
• Coloeus Vigors & Horsfield, 1827
• Corvus Linnaeus, 1758
• Crypsirina Vieillot, 1816
• Cyanocitta Strickland, 1845
• Cyanocorax Boie, 1826
• Cyanolyca Cabanis, 1851
• Cyanopica Bonaparte, 1850
• Dendrocitta Gould, 1833
• Garrulus Brisson, 1760
• Gymnorhinus Wied-Neuwied, 1841
• Nucifraga Brisson, 1760
• Perisoreus Bonaparte, 1831
• Pica Brisson, 1760
• Platylophus Swainson, 1832
• Platysmurus Reichenbach, 1850
• Potential Fischer von Waldheim, 1821
• Psilorhinus Rüppell, 1837
• Ptilostomus Swainson, 1837
• Pyrrhocorax Tunstall, 1771
• Temnurus Lesson, 1830
• Urocissa Cabanis, 1850
• Zavattariornis Moltoni, 1938