Семейство врановых птиц: интеллект и эволюция.

Family of perching birds

Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers. Corvids (ravens) are the largest passerines. 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 higher 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 (most passerines moult twice). 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 hybridization. The presumed corvid relatives included: currawongs, birds of paradise, whipbirds, quail thrushes, whistlers, monarch flycatchers and drongos, shrikes, vireos, and vangas,

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.

Some corvids have strong organization 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 specialized beak for tearing into flesh, they must wait until animals are opened, whether by other predators or as roadkill.

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.

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. 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 of the Corvids are omnivorous, suggesting that they are exposed to more different stimuli and environments. Furthermore, many corvid species live in a large family group, 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 out performed 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 able to be sensitive to other's emotions.

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, define 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 contagions 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 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. 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' behavioral changes to varying human gazes and facial expressions, Clucas et al. (2013) identified that crows are able to change their behaviors to 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.

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. For group living species, there are two opposing hypotheses regarding the assortment of personalities within a group: the social niche specialization 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 behavior over time (personality), by showing that conspecific presence promoted the behavioral 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, 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. although 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.

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. 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, 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 (that is, they remember previous relevant social contexts, use their own experience of having been a thief to predict the behavior 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 for how long. This has been compared to episodic memory, previously thought 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 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.

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.

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 North America, 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.