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Conceptual thinking and social behavior of ravens

Ravens are known to play socially and surveys show that it is correlated with their relatively large brains sizes and extended period of reaching sexual maturity^[1]
The term of social play means ‘play behavior that involves at least two individuals who interact with and respond to each other and are thus capable of exchanging information’^[2] and does not seem to have any direct adaptive advantage.

Social play of avian species is made up of the following: play chasing, play fighting, play invitations and social object play. What suggest that those actions are play, rather than serious competition, is the fact that they are performed slowly, the interactions are reciprocally initiated, and there is no obvious resolution, no winners or losers in the contests^[3]

There were no play invitations observed in ravens; they are much more focused on playful object manipulation and exploratory and innovative behavior, improving their skills and strengthen relationships^[4]

Scientists set out the crucial correlation between altricial development, larger relative brain size and higher degrees of sociality. Extended parental care and prolonged, protected juvenile phases are characteristic of mammalian social development and generally rare among birds. Although, parrots and songbirds (including corvids) have delayed neuronal maturation, what promote learning from conspecifics.^[5] Remaining association between adults and post-fledging juveniles, for example while they aggregate at feeding sites, appears to be essential in promoting complex social play^[6]

Ravens are curious and highly exploratory but when they are older than one month post-fledging, they fear almost anything new. This phenomena named neophobia limits their explorative behaviour and may restrict common sense of searching for novel food sources, learning and innovation^[7]

Ravens reacted differently on the novel objects, depending on presence of conspecifics or being alone. Individuals generally approached faster when tested alone, opposite to the dyad or a group which spend more time close to the novel objects exploring it and manipulating with.^[8] In mixed-sex combinations, both males and females move toward to the novel object later than in same-sex combinations, but there is no difference in time spent close to the items. Also, in the dyadic condition, one bird waits for the other one to take the risk of first approach. Furthermore, in mixed-sex combinations dominant males came first, but in dyads with another male did not. Thus, the sex of the conspecific has a major influence on who is going to make the first approach to the novel objects^[9]

Ravens live in social groups and more willingly share food or attention with kins, spend more time close together and tolerate smaller inter-individual distances, what indicates larger carefulness while approaching to the novel object in group, because they take into account others’ behavior.

During the test in which a series of novel objects were presented to the group of ravens, they gradually lost interest towards these objects. The first one was more attractive for them than the following, also they could be less concentrated due to the repetition and quickly stop participating in experiments when tests were repeated frequently, even though objects were always new^[10]

Many corvids cache food for future consumption. To ably hide nourishment, these species need to distinct the type and perishability of cached item, remember its localization and process information about the social context of caching^[11]
Researches point up ravens’ extraordinary ability to remember not only where they hide which foods, but also how long ago and in which weather conditions. It is crucial while caching perishable food – individuals aware of relative decay rates of particular item did not attempt to recover the rotten one and selectively search for those edible, including fluctuating temperatures.^[12] Furthermore, they could distinguish between different foods cached in the same location or even between two caches containing the same food type, but cached at separate time. Such ability is named episodic-like memory. It is valid to consider that those birds can update their knowledge about for example decay rates and adopt this knowledge to information already encoded^[13]

Ravens do not only cache their own food, but also search for cache sites with nourishment hidden by conspecifics. Individual birds can play both roles. Ethologists put forward that individuals with prior experience of pilfering another bird’s caches are more conscious about the risk of being robbed. They relate information about their earlier behaviour to the possibility of future stealing by another raven and modify their specific strategies of caching, based on their experience of being pilfered previously. Examples of such behavior make up understanding another’s viewpoint, alike preferences to cache in locations less visible to the observer, in a darkened part of a cage, hiding foods behind barriers, leading competitors away from the location of caches, or making false caches that contain either an inedible item, such as a stone, or nothing at all. Widespread and noticeable is a tendency to recache food if the storer has been observed by conspecifics during hiding it.^[14]

Common ravens, a prominent scavenger, are depend upon spatially and temporally ephemeral food sources. They gather information from either conspecifics or nonconspecifics on the location and quality of resources and use kleptoparasitism as a foraging strategy to reduce search time, spending energy and risks of gaining the food themselves^[15]

Achieving information depends on travelling the landscape and visually seeking for food sources or other species hunting, responding to vocalizations from other scavengers, following conspecifics that have previously found food source and preferentially associating with predators. In winter ravens’ foraging strategy is to follow wolfs’ pack and acompanion them while killing and opening the carcasses. It is a form of social symbiosis, in that ravens are stealing food that would otherwise benefit the wolves^[16]

Ravens’ association with grey wolves is not incidental or a product of fresh meat exposed in the area, inversely, they preferentially associate with wolves in both the presence and absence of food. Researchers have hypothesized that ravens monitor wolf pack by following them, following their tracks in the snow or responding to the vocalizations to find wolves’ location. Therefore, wolf-killed carcasses were almost immediately discovered because some ravens were following the pack prior to the kill, throughout the day^[17]

In addition, another aspect of social foraging is the reduction of neophobia^[18] through social facilitation. Ravens are initially fearful of large carcasses, but they lose their caution by observing carcass feeders. This effect of lower neophobia can strengthen ravens foraging success.

On the other side, ravens have not been found to associate with prey animal (e.g. elk) because it is probably not advantageous for ravens to wait for one die, except when animal was injured and draw wolves attention. In like manner, ravens spend less time associating with resting wolves, because those are less likely to kill a prey animal, opposite to travelling ones, who could have the opportunity to hunt.^[19]

Wolves chase and kill kleptoparasitic ravens to defend the carcasses. Although, frequent interactions between these species, such as ravens pulling wolves’ tails, interacting with wolves’ pups at den sites, and playful chasing between them (Stahler, 2000) result educating the birds on potential dangerousness of being close to large carnivores.

Ravens possess a large repertoire of calls. During their immature phase of about 3 years, they interact with many individuals, when they are vagrant. Therefore, there are more opportunities for interactions under natural conditions, rather than among captive ravens. Depending on who is learning what, when and from whom, various patterns of cultural transmission may arise. Cultural transmission is the spread of behavior by social learning, e.g. vocal learning, amid conspecifics. That explains why call types are unequally distributed among individuals^[20]

There is no significant difference in repertoire size between males and females, however, some calls are used more often by one sex than the other. This is a kind of sexual dimorphism, culturally determined, as a result of small amount of morphological differences (same colour, similar body size and slight distinction in beak form); marked sex-specific repertoire composition seems to be substantial. Moreover, bidirectional transmission of vocalizations is also found in ravens, because some call types are observed in an individual only if they are either in the repertoire of its partner. Scientists pointed out that single birds choose partners with shared calls in their repertoire.^[21]