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 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 of the Corvids are omnivorous, suggesting that they are exposed to a wider variety of 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.
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, 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 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' behavioural changes to varying human gazes and facial expressions, Clucas et al. (2013) identified that crows are able to change their behaviour 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.
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 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.
Social construction 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.
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,
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 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, 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 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. ==Disease==