Thomas Bugnyar

Observational learning and the raiding of food caches in ravens, Corvus corax: is it 'tactical' deception?

Abstract Group-foraging ravens scatter-hoard when they are competing for food and, to some extent, also raid the caches made by others. We investigated the effects of observational spatial memory on individual caching and raiding tactics. With captive ravens, we found visual observation was essential for locating and raiding the caches of conspecifics. Both captive and free-ranging ravens, food cachers as well as potential cache raiders, responded to each others presence. Cachers withdrew from conspecifics and most often placed their caches behind structures, obstructing the view of potential observers. Raiders watched inconspicuously and kept at a distance to cachers close to their cache sites. In response to the presence of potential raiders or because of their initial movements towards caches, the cachers frequently interrupted caching, changed cache sites, or recovered their food items. These results suggest that ravens, regardless of whether they act as cachers or raiders, are capable of withholding information about their intentions and, hence, manipulate the other birds attention either to prevent or to achieve social-learning opportunities. Such interactions may qualify as ‘tactical’ deception and may have created a considerable pressure selecting for social cognition in ravens. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .

Ravens, Corvus corax, follow gaze direction of humans around obstacles

The ability to follow gaze (i.e. head and eye direction) has recently been shown for social mammals, particularly primates. In most studies, individuals could use gaze direction as a behavioural cue without understanding that the view of others may be different from their own. Here, we show that hand–raised ravens not only visually co–orient with the look–ups of a human experimenter but also reposition themselves to follow the experimenters gaze around a visual barrier. Birds were capable of visual co–orientation already as fledglings but consistently tracked gaze direction behind obstacles not before six months of age. These results raise the possibility that sub–adult and adult ravens can project a line of sight for the other person into the distance. To what extent ravens may attribute mental significance to the visual behaviour of others is discussed.

Push or pull: an experimental study on imitation in marmosets

A laboratory experiment was conducted in order to explore the possibility of imitation, that is, response learning by observation, in marmosets, Callithrix jacchusInexperienced individuals were allowed to observe a skilful model that demonstrated one of two possible techniques (pushing or pulling a pendulum-door) to get food from inside a wooden box. Their initial manipulative actions, performed when exposed to the box in a subsequent test, were compared with those of naive control subjects (non-observers). The observers showed less exploratory behaviour than the non-observers and, more importantly, some showed a strong tendency to use the demonstrated opening technique in the initial test phase. This initial preference disappeared in the course of five test sessions and the observers converged towards the simpler, alternative solution that was generally preferred by the non-observers. Despite fundamental individual differences in the observer group and the failure to find a significant group effect, the results indicate that marmosets are capable of learning simple motor skills through conspecific observation.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

The quality of social relationships in ravens

The quality of a social relationship represents the history of past social interactions between two individuals, from which the nature and outcome of future interactions can be predicted. Current theory predicts that relationship quality comprises three separate components, its value, compatibility and security. This study is the first to investigate the components of relationship quality in a large-brained bird. Following methods recently used to obtain quantitative measures of each relationship quality component in chimpanzees, Pan troglodytes, we entered data on seven behavioural variables from a group of 11 ravens, Corvus corax, into a principal components analysis. The characteristics of the extracted components matched those predicted for value, compatibility and security, and were labelled as such. When the effects of kinship and sex combination on each relationship quality component were analysed, we found that kin had more valuable relationships, whereas females had less secure and compatible relationships, although the effect of sex combination on compatibility only applied to nonkin. These patterns are consistent with what little knowledge we have of raven relationships from aviary studies and show that the components of relationship quality in ravens may indeed be analogous to those in chimpanzees.

Gaze following in the red-footed tortoise (Geochelone carbonaria)

Gaze following refers to the ability of an animal to orient its gaze direction to that of another organism. Such a behavior may be adaptive as it alerts the observer to important objects in the environment such as food or predators. This behavior has been shown in mammals and birds, but the evolutionary history and the distribution of this behavior throughout the animal kingdom remain unclear. Here, we show that a reptile, the red-footed tortoise (Geochelone carbonaria), is able to follow the gaze of a conspecific in a lookup task. Controls revealed that neither the mere presence of a conspecific nor the presentation of a light stimulus (without a demonstrator present) controlled the tortoises’ behavior. The findings indicate that the ability to follow gaze may be found in mammals, birds and reptiles and could have evolved before the amniotic line diverged, or may result from a general ability to learn.

Cognition without Cortex

Assumptions on the neural basis of cognition usually focus on cortical mechanisms. Birds have no cortex, but recent studies in parrots and corvids show that their cognitive skills are on par with primates. These cognitive findings are accompanied by neurobiological discoveries that reveal avian and mammalian forebrains are homologous, and show similarities in connectivity and function down to the cellular level. But because birds have a large pallium, but no cortex, a specific cortical architecture cannot be a requirement for advanced cognitive skills. During the long parallel evolution of mammals and birds, several neural mechanisms for cognition and complex behaviors may have converged despite an overall forebrain organization that is otherwise vastly different.

Enhanced social learning between siblings in common ravens, Corvus corax

It has been suggested that social dynamics affect social learning but empirical support for this idea is scarce. Here we show that affiliate relationships among kin indeed enhance the performance of common ravens, Corvus corax, in a social learning task. Via daily behavioural protocols we first monitored social dynamics in our group of captive young ravens. Siblings spent significantly more time in close proximity to each other than did nonsiblings. We subsequently tested birds on a stimulus enhancement task in model-observer dyads composed of both siblings and nonsiblings. During demonstration the observer could watch the model manipulating one particular object (target object) in an adjacent room. After removing the model, the observer was confronted with five different objects including the former target object. Observers from sibling dyads handled the target object for significantly longer periods of time as compared with the other four available objects, whereas observers from nonsibling dyads did not show a preference for the target object. Also, siblings matched the models decision to cache or not to cache objects significantly more often than did nonsiblings. Hence, siblings were likely to attend to both, the behaviour of the model (caching or noncaching) and object-specific details. Our results support the hypothesis that affiliate relations between individuals affect the transmission of information and may lead to directed social learning even when spatial proximity has been experimentally controlled for.

The ontogeny of caching in ravens, Corvus corax

Ravens scavenging on carcasses devote much of their time to carrying off loads of food for temporary storage in caches. Ways of reducing conspecific pilfering of these caches include camouflaging caches with debris and positioning caches at a distance from and/or out of sight of potential competitors. We examined the acquisition and improvement of these caching skills in young captive ravens. We identified a hierarchy of elements in the caching behaviour, ranging from simply pressing the caching items towards solid structures to the appropriate covering of them with surrounding material. The development of these elements was closely linked with the birds’ acquisition of Piagetian Stages of object permanence. Furthermore, we distinguished between the young ravens’ initial caching of edible and inedible items. We tracked the individuals’ temporal development of placing their caches at a distance from and out of sight of conspecifics and their social interactions over caches. Behaviours aimed at preventing pilfering were associated with competitive interactions and were manifested only with edible items. We conclude that the skills for camouflaging caches are primarily affected by maturation of representational capacities for hidden (i.e. not visible) items, whereas the skills for the positioning of caches are strongly affected by experience gained through social interactions.

Reciprocity of agonistic support in ravens

Cooperative behaviour through reciprocation or interchange of valuable services in primates has received considerable attention, especially regarding the timeframe of reciprocation and its ensuing cognitive implications. Much less, however, is known about reciprocity in other animals, particularly birds. We investigated patterns of agonistic support (defined as a third party intervening in an ongoing conflict to attack one of the conflict participants, thus supporting the other) in a group of 13 captive ravens, Corvus corax. We found support for long-term, but not short-term, reciprocation of agonistic support. Ravens were more likely to support individuals who preened them, kin and dominant group members. These results suggest that ravens do not reciprocate on a calculated tit-for-tat basis, but aid individuals from whom reciprocated support would be most useful and those with whom they share a good relationship. Additionally, dyadic levels of agonistic support and consolation (postconflict affiliation from a bystander to the victim) correlated strongly with each other, but we found no evidence to suggest that receiving agonistic support influences the victim’s likelihood of receiving support (consolation) after the conflict ends. Our findings are consistent with an emotionally mediated form of reciprocity in ravens and provide additional support for convergent cognitive evolution in birds and mammals.

Do common ravens (Corvus corax) rely on human or conspecific gaze cues to detect hidden food

The ability of non-human animals to use experimenter-given cues in object-choice tasks has recently gained interest. In such experiments, the location of hidden food is indicated by an experimenter, e.g. by gazing, pointing or touching. Whereas dogs apparently outperform all other species so far tested, apes and monkeys have problems in using such cues. Since only mammalian species have been tested, information is lacking about the evolutionary origin of these abilities. We here present the first data on object-choice tasks conducted with an avian species, the common raven. Ravens are highly competitive scavengers, possessing sophisticated cognitive skills in protecting their food caches and pilfering others’ caches. We conducted three experiments, exploring (i) which kind of cues ravens use for choosing a certain object, (ii) whether ravens use humans’ gaze for detecting hidden food and (iii) whether ravens would find hidden food in the presence of an informed conspecific who potentially provides gaze cues. Our results indicate that ravens reliably respond to humans’ touching of an object, but they hardly use point and gaze cues for their choices. Likewise, they do not perform above chance level in the presence of an informed conspecific. These findings mirror those obtained for primates and suggest that, although ravens may be aware of the gaze direction of humans and conspecifics, they apparently do not rely on this information to detect hidden food.