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| Author |
Bugnyar, T.; Kotrschal, K. |
| Title |
Movement coordination and signalling in ravens (Corvus corax): an experimental field study |
Type |
Journal Article |
Year  |
2001 |
Publication |
Acta ethologica |
Abbreviated Journal |
Acta. Ethol. |
| Volume |
3 |
Issue |
2 |
Pages |
101-109 |
| Keywords |
Ravens – Corvus corax – Foraging – Coordination – Communication |
| Abstract |
Vagrant non-breeding ravens frequently attract conspecifics to rich ephemeral food sources. There, grouping may allow them to overcome the defence of territorial breeders. Here, we focus on ravens making use of regular food supplies in a game park, where they divert food from the provision of park animals. We investigated if ravens foraging in the Cumberland game park (Grünau, Austria) are attentive towards one another when they experience some unpredictability in food provisioning. We confronted a group of 30-50 ravens with two different treatments. Ten minutes ahead of the feeding of either wolves or wild boars we showed buckets containing pieces of meat to the ravens flying overhead. In the reliable cue treatment (RCT), the meat was placed next to one of the two enclosures, whereas in the unreliable cue treatment (UCT), the buckets were placed simultaneously in front of both enclosures though only in one of the enclosures were the animals fed 10 min later. Thus, during RCT but not during UCT, ravens could predict where food would become available. Only during UCT, ravens moved in large groups between the two feeding sites. Many ravens moving at the same time in the same direction may indicate some co-ordination in space and time, which is most likely achieved by social attraction among individuals. Furthermore, the number of ravens approaching and leaving, respectively, a feeding site cross-correlated with a temporary increase in the rate of a food-associated call, the yell. This suggests that in addition to watching each other, calling may have contributed to group formation. Possible benefits of group formation during food inspection are discussed. |
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2081 |
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Bugnyar, T.; Kotrschal, K. |
| Title |
Observational learning and the raiding of food caches in ravens, Corvus corax: is it `tactical' deception? |
Type |
Journal Article |
| Year |
2002 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
64 |
Issue |
2 |
Pages |
185-195 |
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| 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 other's 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 bird's 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. |
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Equine Behaviour @ team @ |
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2904 |
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Bugnyar, T.; Kotrschal, K. |
| Title |
Leading a conspecific away from food in ravens ( Corvus corax)? |
Type |
Journal Article |
| Year |
2004 |
Publication |
Animal Cognition |
Abbreviated Journal |
Anim. Cogn. |
| Volume |
7 |
Issue |
2 |
Pages |
69-76 |
| Keywords |
Misleading – Deception – Raven – Social foraging |
| Abstract |
Active misleading of conspecifics has been described as a social strategy mainly for primates. Here we report a raven leading a competitor away from food in a social foraging task. Four individuals had to search and compete for hidden food at color-marked clusters of artificial food caches. At the beginning of the experiment, a subordinate male found and exploited the majority of the food. As a result, the dominant male displaced him from the already opened boxes. The subordinate male then developed a pattern, when the loss of reward to the dominant got high, of moving to unrewarded clusters and opening boxes there. This diversion often led the dominant to approach those unrewarded clusters and the subordinate then had a head start for exploiting the rewarded boxes. Subsequently, however, the dominant male learned not to follow the subordinate to unrewarded clusters and eventually started searching for the reward himself. These interactions between the two males illustrate the ravens' potential for deceptively manipulating conspecifics. We discuss under which circumstances ravens might use this capacity. |
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2080 |
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Bugnyar, T.; Stöwe, M.; Heinrich, B. |
| Title |
Ravens, Corvus corax, follow gaze direction of humans around obstacles |
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Journal Article |
| Year |
2004 |
Publication |
Proceedings of the Royal Society B: Biological Sciences |
Abbreviated Journal |
Proc. Roy. Soc. Lond. B Biol. Sci. |
| Volume |
271 |
Issue |
1546 |
Pages |
1331-1336 |
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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 experimenter's 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. |
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10.1098/rspb.2004.2738 |
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Equine Behaviour @ team @ |
Serial |
5009 |
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Bugnyar, T.; Heinrich, B. |
| Title |
Pilfering ravens, Corvus corax, adjust their behaviour to social context and identity of competitors |
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Journal Article |
| Year |
2006 |
Publication |
Animal Cognition |
Abbreviated Journal |
Anim. Cogn. |
| Volume |
9 |
Issue |
4 |
Pages |
369-376 |
| Keywords |
Adaptation, Psychological; Animals; *Behavior, Animal; *Competitive Behavior; Crows/*physiology; *Deception; Feeding Behavior; Female; Male; Social Behavior; *Social Environment |
| Abstract |
Like other corvids, food-storing ravens protect their caches from being pilfered by conspecifics by means of aggression and by re-caching. In the wild and in captivity, potential pilferers rarely approach caches until the storers have left the cache vicinity. When storers are experimentally prevented from leaving, pilferers first search at places other than the cache sites. These behaviours raise the possibility that ravens are capable of withholding intentions and providing false information to avoid provoking the storers' aggression for cache protection. Alternatively, birds may refrain from pilfering to avoid conflicts with dominants. Here we examined whether ravens adjust their pilfer tactics according to social context and type of competitors. We allowed birds that had witnessed a conspecific making caches to pilfer those caches either in private, together with the storer, or together with a conspecific bystander that had not created the caches (non-storer) but had seen them being made. Compared to in-private trials, ravens delayed approaching the caches only in the presence of storers. Furthermore, they quickly engaged in searching away from the caches when together with dominant storers but directly approached the caches when together with dominant non-storers. These findings demonstrate that ravens selectively alter their pilfer behaviour with those individuals that are likely to defend the caches (storers) and support the interpretation that they are deceptively manipulating the others' behaviour. |
| Address |
Department of Biology, University of Vermont, Burlington, VT 05405, USA. thomas.bugnyar@univie.ac.at |
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English |
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1435-9448 |
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PMID:16909235 |
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no |
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Equine Behaviour @ team @ |
Serial |
2449 |
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Range, F.; Bugnyar, T.; Schlogl, C.; Kotrschal, K. |
| Title |
Individual and sex differences in learning abilities of ravens |
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Journal Article |
| Year |
2006 |
Publication |
Behavioural Processes |
Abbreviated Journal |
Behav. Process. |
| Volume |
73 |
Issue |
1 |
Pages |
100-106 |
| Keywords |
Animals; Behavior, Animal/*physiology; *Crows; Discrimination Learning/*physiology; Exploratory Behavior/physiology; Female; *Individuality; Male; Sex Factors; Spatial Behavior |
| Abstract |
Behavioral and physiological characteristics of individuals within the same species have been found to be stable across time and contexts. In this study, we investigated individual differences in learning abilities and object and social manipulation to test for consistency within individuals across different tasks. Individual ravens (Corvus corax) were tested in simple color and position discrimination tasks to establish their learning abilities. We found that males were significantly better in the acquisition of the first discrimination task and the object manipulation task, but not in any of the other tasks. Furthermore, faster learners engaged less often in manipulations of conspecifics and exploration of objects to get access to food. No relationship between object and social manipulation and reversal training were found. Our results suggest that individual differences in regard to the acquisition of new tasks may be related to personalities or at least object manipulation in ravens. |
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Konrad Lorenz Research Station, A-4645 Gruenau 11, Austria. friederike.range@univie.ac.at |
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English |
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0376-6357 |
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PMID:16675158 |
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no |
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Equine Behaviour @ team @ |
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4146 |
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Heinrich, B.; Bugnyar, T. |
| Title |
Just how smart are ravens? |
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Journal Article |
| Year |
2007 |
Publication |
Scientific American |
Abbreviated Journal |
Sci Am |
| Volume |
296 |
Issue |
4 |
Pages |
64-71 |
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Animals; *Behavior, Animal; Crows/*physiology; Environment; *Intelligence; Predatory Behavior; Problem Solving; Thinking |
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University of Vermont, USA |
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English |
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0036-8733 |
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PMID:17479632 |
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Equine Behaviour @ team @ |
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4101 |
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Schloegl, C.; Kotrschal, K.; Bugnyar, T. |
| Title |
Gaze following in common ravens, Corvus corax: ontogeny and habituation |
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Journal Article |
| Year |
2007 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
74 |
Issue |
4 |
Pages |
769-778 |
| Keywords |
Corvus corax; gaze following; habituation; ontogenetic development; raven |
| Abstract |
Co-orientation with others by using their gaze direction is considered to be adaptive for detecting food or predators or monitoring social interactions. Like the great apes, common ravens are capable of following human experimenters' gaze direction not only into distant space but also behind visual barriers. We investigated the ontogenetic development of these abilities by confronting birds with a human foster parent looking up (experiment 1) and behind visual barriers (experiment 3) and their modification by habituation (experiments 2 and 4). We tested a group of 12 hand-reared ravens during their first 10 months of life. Ravens responded to others' look-ups soon after fledging but could track their gaze behind a visual barrier only 4 months later, at the age they usually become independent from their parents. Furthermore, ravens quickly ceased responding to repeated look-ups by the model, but did not habituate to repeated gaze cues directed behind a barrier. Our findings support the idea that the two modes of gaze following reflect different cognitive levels in ravens and, possibly, have different functions. |
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Equine Behaviour @ team @ |
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4204 |
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Schloegl, C.; Kotrschal, K.; Bugnyar, T. |
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Modifying the object-choice task: Is the way you look important for ravens? |
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Journal Article |
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2008 |
Publication |
Behavioural Processes |
Abbreviated Journal |
Behav. Process. |
| Volume |
77 |
Issue |
1 |
Pages |
61-65 |
| Keywords |
Gaze; Modification; Object-choice task; Raven |
| Abstract |
Most animals seem to have difficulties in using gaze cues to find hidden food in object-choice tasks. For instance, chimpanzees usually fail in these tests, even though they are capable of following other's gaze geometrically behind barriers. Similar to chimpanzees, common ravens are skilled in tracking other's gaze but fail in object-choice tasks. We here explored whether procedural modifications, which had been used successfully in chimpanzees, would also yield positive results in ravens. In our modifications (a) the experimenter approached the cup while gazing at it, (b) the gaze cue was accompanied by a sound and (c) the experimenter could actually see the food while giving the gaze cue. Two out of seven birds performed above chance level in some of these conditions. However, we ascribe this improvement to the individuals' learning ability rather than to an understanding of the communicative nature of the task. This interpretation is further supported by results of a follow-up experiment suggesting that ravens may not rely on conspecifics' gaze cues for finding food caches in a natural foraging context. In sum, our results suggest that ravens may not transfer their gaze follow abilities to foraging situations involving hidden food. |
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Equine Behaviour @ team @ |
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4505 |
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Schwab, C.; Bugnyar, T.; Schloegl, C.; Kotrschal, K. |
| Title |
Enhanced social learning between siblings in common ravens, Corvus corax |
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Journal Article |
| Year |
2008 |
Publication |
Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
| Volume |
75 |
Issue |
2 |
Pages |
501-508 |
| Keywords |
affiliation; cognition; common raven; Corvus corax; siblings; social learning; social relations |
| Abstract |
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 model's 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. |
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0003-3472 |
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Equine Behaviour @ team @ |
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5300 |
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