The performance of ravens on simple discrimination tasks: a preliminary study

Recent studies suggest the existence of primate-like cognitive abilities in corvids. Although the learning abilities of corvids in comparison to other species have been investigated before, little is known on how corvids perform on simple discrimination tasks if tested in experimental settings comparable to those that have been used for studying complex cognitive abilities. In this study, we tested a captive group of 12 ravens (Corvus corax) on four discrimination problems and their reversals. In contrast to other studies investigating learning abilities, our ravens were not food deprived and participation in experiments was voluntary. This preliminary study showed that all ravens successfully solved feature and position discriminations and several of the ravens could solve new tasks in a few trials, making very few mistakes.     

Socially Driven Consistent Behavioural Differences during Development in Common Ravens and Carrion Crows

Consistent individual differences in behaviour, or ‘personality’, are likely to be influenced by development, social context, and species ecology, though few comparative, longitudinal studies exist. Here, we investigated the role of development and social context on personality variation in two identically reared, social corvids: common ravens and carrion crows. We repeatedly presented subjects with a variety of novel food and objects, while alone and in a primarily sibling subgroup, from fledging to sub-adulthood. We predicted that consistent individual differences would emerge later in development, and that conspecific presence would facilitate behavioural similarities. In contrast to our predictions, we found that individuals of both species were highly inconsistent in their behavioural responses throughout the development period. In line with our predictions, though in the ravens only, conspecific presence promoted behavioural similarities as individuals were strongly shaped by their subgroup, and it is likely that these effects were driven by social context rather than relatedness. We discuss these findings in relation to developmental steps and the role of social relations in these species. Overall, our findings highlight that these two species are highly adaptable in their behaviour, and the ravens in particular are strongly influenced by their social environment, which may facilitate cooperation and social learning.     

Individual differences in learning behaviours in humans: Asocial exploration tendency does not predict reliance on social learning

A number of empirical studies have suggested that individual differences in asocial exploration tendencies in animals may be related to those in social information use. However, because the ‘exploration tendency’ in most previous studies has been measured without considering the information-gathering processes, it is yet hard to conclude that the animal asocial exploration strategies may be tied to social information use. Here, we studied human learning behaviour in both asocial and social two-armed bandit tasks. By fitting reinforcement learning models including asocial and/or social decision processes, we measured each individual's (1) asocial exploration tendency and (2) social information use. We found consistent individual differences in the exploration tendency in the asocial tasks. We also found substantive heterogeneity in the adopted learning strategies in the social task: Nearly one-third of participants used predominantly the copy-when-uncertain strategy, while the remaining two-thirds were most likely to have relied only on asocial learning. However, we found no significant individual association between the exploration frequency in the asocial task and the use of the social information in the social task. Our results suggest that the social learning strategies may be independent from the asocial exploration strategies in humans.     

Behavioural and Hormonal Stress Responses to Social Separation in Ravens,Corvus corax

Social life is profitable, but it facilitates conflicts over resources and creates interdependence between individuals. Separating highly social animals triggers intense reactions aimed at re‐establishing lost connections. Less is known, however, about behavioural and physiological responses to separation in socially facultative species, where individuals temporarily form groups and may subsequently leave them. Non‐breeding common ravens (Corvus corax) gather in large numbers at feeding and roosting sites, but otherwise spend time seemingly solitary or in small subgroups. We here studied how ravens cope with being socially isolated, and investigated the life characteristics that might explain potential individual differences. For this, we individually separated captive subadult ravens (n = 25) and housed them in physical and visual isolation from their group members across 4 d. During the separation period, we collected behavioural data and measured the amount of immunoreactive corticosterone metabolites from bird droppings to assess the ravens’ physiological stress response. We found behavioural indicators of stress at the start of the separation, when ravens showed higher levels of tension than of comfort – a pattern that reversed at the end of the separation. Furthermore, we found that the upbringing of ravens affected their behaviour during separation. Hand‐raised birds produced more vocalisations in the beginning of the separation, and were less active at the end, while the reverse pattern occurred with parent‐raised ravens. Contrary to our predictions, we did not find differences in hormonal responses between the beginning and end of the separation period or any link between hormonal responses and behaviours. Ravens’ behavioural responses to social separation stress seem to be dependent on their arousal states, although possible links with hormonal reactions remain unclear. Our results show that behavioural reactions are not always linked with hormonal responses to stress, and further emphasise the importance of investigating effects of early‐life experiences.     

Flexibility in Food Extraction Techniques in Urban Free-Ranging Bonnet Macaques,Macaca radiata

Non-human primate populations, other than responding appropriately to naturally occurring challenges, also need to cope with anthropogenic factors such as environmental pollution, resource depletion, and habitat destruction. Populations and individuals are likely to show considerable variations in food extraction abilities, with some populations and individuals more efficient than others at exploiting a set of resources. In this study, we examined among urban free-ranging bonnet macaques, Macaca radiata (a) local differences in food extraction abilities, (b) between-individual variation and within-individual consistency in problem-solving success and the underlying problem-solving characteristics, and (c) behavioral patterns associated with higher efficiency in food extraction. When presented with novel food extraction tasks, the urban macaques having more frequent exposure to novel physical objects in their surroundings, extracted food material from PET bottles and also solved another food extraction task (i.e., extracting an orange from a wire mesh box), more often than those living under more natural conditions. Adults solved the tasks more frequently than juveniles, and females more frequently than males. Both solution-technique and problem-solving characteristics varied across individuals but remained consistent within each individual across the successive presentations of PET bottles. The macaques that solved the tasks showed lesser within-individual variation in their food extraction behavior as compared to those that failed to solve the tasks. A few macaques appropriately modified their problem-solving behavior in accordance with the task requirements and solved the modified versions of the tasks without trial-and-error learning. These observations are ecologically relevant – they demonstrate considerable local differences in food extraction abilities, between-individual variation and within-individual consistency in food extraction techniques among free-ranging bonnet macaques, possibly affecting the species’ local adaptability and resilience to environmental changes.     

Guppies learn faster to discriminate between red and yellow than between two shapes

Animal species are expected to evolve specialised cognitive abilities to solve the tasks that are critical for their fitness. The literature contains several examples of specialised cognitive abilities, but few regard fish. The guppy, Poecilia reticulata, is a freshwater fish in which females choose their mates based on colouration, and orange‐coloured fruits are important diet enrichments for both sexes. For these reasons, we expect that this species has evolved enhanced learning abilities in colour discrimination compared to other types of discrimination. The comparison between studies in which guppies were tested for colour discrimination and studies in which guppies were tested for shape discrimination seems to support this hypothesis, but direct testing is still lacking. We experimentally compared the learning performance of guppies trained in a red–yellow colour discrimination learning task and that of guppies trained in a shape discrimination learning task using the same, automated conditioning procedure. Guppies trained in the colour discrimination showed greater learning performance, which provides support to the hypothesis that guppies possess enhanced colour discrimination abilities. Moreover, we found that male guppies performed better than females in both shape and colour discrimination learning.     

Social context hinders humans but not ravens in a short-term memory task

Using resources shared within a social group—either in a cooperative or a competitive way—requires keeping track of own and others’ actions, which, in turn, requires well-developed short-term memory. Although short-term memory has been tested in social mammal species, little is known about this capacity in highly social birds, such as ravens. We compared ravens (Corvus corax) with humans in spatial tasks based on caching, which required short-term memory of one's own and of others’ actions. Human short-term memory has been most extensively tested of all social mammal species, hence providing an informative benchmark for the ravens. A recent study on another corvid species (Corvus corone) suggests their capacity to be similar to the humans’, but short-term memory skills have, to date, not been compared in a social setting. We used spatial setups based on caches of foods or objects, divided into individual and social conditions with two different spatial arrangements of caches (in a row or a 3 × 3 matrix). In each trial, a set of three up to nine caches was presented to an individual that was thereafter allowed to retrieve all items. Humans performed better on average across trials, but their performance dropped, when they had to keep track of partner's actions. This differed in ravens, as keeping track of such actions did not impair their performance. However, both humans and ravens demonstrated more memory-related mistakes in the social than in the individual conditions. Therefore, whereas both the ravens’ and the humans’ memory suffered in the social conditions, the ravens seemed to deal better with the demands of these conditions. The social conditions had a competitive element, and one might speculate that ravens’ memory strategies are more attuned to such situations, in particular in caching contexts, than is the case for humans.     

Novel object exploration in ravens (Corvus corax): effects of social relationships

Social context has been shown to encourage, or to delay object exploration and learning. This ambiguity might be due to factors such as social relationships and personality of the individuals involved. Here, we investigated in ravens (Corvus corax) individuals' consistency in response to novel objects over development and across contexts: alone versus social. In the social setting we focussed on the effects of social relationships on social facilitation during the approach to novel objects. We tested 11 hand-raised ravens with novel objects individually at three and six months of age and in dyadic combinations at six months of age. Individuals were consistent over development and contexts in their response to different novel objects. Birds joined siblings faster to approach novel objects than non-siblings. They also spent more time sitting close to siblings than to non-siblings. In male-male dyads but not in female-female dyads, subordinates approached the novel objects significantly faster than dominant birds. In contrast, dominant males were the first to approach the novel objects in mixed-sex combinations. Hence, the effect of social context seems to depend on the social relationships towards the companions and on the combination of the sexes.     

Does Innovation Success Influence Social Interactions? An Experimental Test in House Sparrows

In group‐living animals, individuals may benefit from the presence of an innovative group‐mate because new resources made available by innovators can be exploited, for example by scrounging or social learning. As a consequence, it may pay off to take the group‐mates' problem‐solving abilities into account in social interactions such as aggression or spatial association, for example because dominance over an innovative group‐mate can increase scrounging success, while spatial proximity may increase the chance of both direct exploitation and social learning. In this study, we tested whether the individuals' innovation success influences their social interactions with group‐mates in small captive flocks of house sparrows (Passer domesticus). First, we measured the birds' actual problem‐solving success in individual food‐extracting tasks. Then, we manipulated their apparent problem‐solving success in one task (by allowing or not allowing them to open a feeder repeatedly) while a new, unfamiliar group‐member (focal individual) had the opportunity to witness their performance. After this manipulation, we observed the frequency and intensity of aggression and the frequency of spatial associations between the focal individuals and their manipulated flock‐mates. Although flock‐mates behaved according to their treatments during manipulations, their apparent problem‐solving success did not affect significantly the focal individuals' agonistic behaviour or spatial associations. These results do not support that sparrows take flock‐mates' problem‐solving abilities into account during social interactions. However, focal individuals attacked those flock‐mates more frequently that had higher actual problem‐solving success (not witnessed directly by the focal individuals), although aggression intensity and spatial association by the focal birds were unrelated to the flock‐mates' actual success. If this association between flock‐mates' actual innovativeness and focal individuals' aggression is not due to confounding effects, it may imply that house sparrows can use more subtle cues to assess the group‐mates' problem‐solving ability than direct observation of their performance in simple foraging tasks.     

Human temporal behavior and discrimination-reversal learning

The present study demonstrates that a relationship exists between individual differences in temporal behavior and individual differences in human discrimination-reversal learning behavior. When the results of performance on a time-estimation task employing the method of reproduction are compared with the results of acquisition performance on a complex form of discrimination-reversal learning task is can be demonstrated that underestimation of time is associated with faster learning and overestimation of time is associated with slower learning of the discrimination task. The experimental design was based on the historical fact that the Sechenov-Pavlov and Spence-Hull formulations assigned a primary role in learning to excitation and inhibition as intervening variables between the input of stimulation and output of response. The present study also used the tasks of time estimation and discrimination learning as dependent variables; and the concept that underestimation of time is associated with and underlying predominance of excitatory processes as a hypothetical construct. The conclusion was reached that one of the many theoretical processes which may be used to explain discrimination learning is the concept that acquisition of the correct response may be viewed as a function of the individual rates at which excitatory processes come to be conditioned to a predominance over existing inhibitory processes.     

Unleashing the BEAST: a brief measure of human social information use

Social information enables individuals to reduce uncertainty and increase decision accuracy across a broad range of domains. Intriguingly, individuals and populations consistently differ in social information use. Understanding the underlying causes of this variation has proven challenging due to the lack of a standardized paradigm to quantify social information use. Here we introduce the BEAST (Berlin Estimate AdjuStment Task); a brief (∼5-min), simple, and incentive-compatible behavioural task to quantify individuals' propensities to use social information. In the task, participants observe an image with a number of animals and estimate the total number. Next, they receive another person's estimate, after which they provide a second estimate. An individual's average adjustment quantifies their propensity to use social information. We found that individuals' propensity to use social information is consistent within the task, has considerable test–retest reliability over 9 months, generalizes to other social learning tasks, and correlates with established self-reported measures of social conformity and social proximity. The BEAST thus reliably captures individual variation in social information use. We conclude by highlighting the BEAST's potential to serve as a flexible framework to assess the determinants of human social information use.     

Early learning in the common marmoset (Callithrix jacchus): Behavior in the family group is related to preadolescent cognitive performance

Early environment can have a major impact on development, with family life known to play an important role. Longitudinal studies can therefore help increase our understanding of variance in cognitive abilities in young animals, as well as over time. We followed 22 marmosets (11 male and 11 female) from infancy through to early adolescence. At 3 months old, the marmosets were trained to reliably touch a rewarded stimulus. At 5 months, behavior was observed within the natal group. At 9 months, the marmosets were given a visual discrimination task to assess learning ability. Mann–Whitney U tests found no sex or family size differences in number of errors at 3 or 9 months. While no significant relationships were found between behavior in the family and learning at 3 months, significant negative correlations were found between duration spent in locomotion and learning errors (p = .05), as well as between frequency of calm vocalizations and learning errors (p = .001) at 9 months. A U-shape curve was found between amount of social play and learning at 9 months. Positive family interactions, including moderate amounts of play, as well as calm individual behavior, may therefore be important in learning. This study sheds light on cognitive development in much younger marmosets than previously studied, and helps increase understanding of how individual differences in learning may arise.     

Inattentional Blindness and Individual Differences in Cognitive Abilities

People sometimes fail to notice salient unexpected objects when their attention is otherwise occupied, a phenomenon known as inattentional blindness. To explore individual differences in inattentional blindness, we employed both static and dynamic tasks that either presented the unexpected object away from the focus of attention (spatial) or near the focus of attention (central). We hypothesized that noticing in central tasks might be driven by the availability of cognitive resources like working memory, and that noticing in spatial tasks might be driven by the limits on spatial attention like attention breadth. However, none of the cognitive measures predicted noticing in the dynamic central task or in either the static or dynamic spatial task. Only in the central static task did working memory capacity predict noticing, and that relationship was fairly weak. Furthermore, whether or not participants noticed an unexpected object in a static task was only weakly associated with their odds of noticing an unexpected object in a dynamic task. Taken together, our results are largely consistent with the notion that noticing unexpected objects is driven more by stochastic processes common to all people than by stable individual differences in cognitive abilities.     

Individual acquisition of “stick pounding” behavior by naïve chimpanzees

Many studies investigating culture in nonhuman animals tend to focus on the inferred need of social learning mechanisms that transmit the form of a behavior to explain the population differences observed in wild animal behavioral repertoires. This research focus often results in studies overlooking the possibility of individuals being able to develop behavioral forms without requiring social learning. The disregard of individual learning abilities is most clearly observed in the nonhuman great ape literature, where there is a persistent claim that chimpanzee behaviors, in particular, require various forms of social learning mechanisms. These special social learning abilities have been argued to explain the acquisition of the relatively large behavioral repertoires observed across chimpanzee populations. However, current evidence suggests that although low‐fidelity social learning plays a role in harmonizing and stabilizing the frequency of behaviors within chimpanzee populations, some (if not all) of the forms that chimpanzee behaviors take may develop independently of social learning. If so, they would be latent solutions—behavioral forms that can (re‐)emerge even in the absence of observational opportunities, via individual (re)innovations. Through a combination of individual and low‐fidelity social learning, the population‐wide patterns of behaviors observed in great ape species are then established and stably maintained. This is the Zone of Latent Solutions (ZLS) hypothesis. The current study experimentally tested the ZLS hypothesis for pestle pounding, a wild chimpanzee behavior. We tested the reinnovation of this behavior in semi‐wild chimpanzees at Chimfunshi Wildlife Orphanage in Zambia, Africa, (N = 90, tested in four social groups). Crucially, all subjects were naïve to stick pounding before testing. Three out of the four tested groups reinnovated stick pounding—clearly demonstrating that this behavioral form does not require social learning. These findings provide support for the ZLS hypothesis alongside further evidence for the individual learning abilities of chimpanzees.     

Low-level correlations between object properties and viewpoint can cause viewpoint-dependent object recognition

Viewpoint-dependent recognition performance of 3-D objects has often been taken as an indication of a viewpoint-dependent object representation. This viewpoint dependence is most often found using metrically manipulated objects. We aim to investigate whether instead these results can be explained by viewpoint and object property (e.g. curvature) information not being processed independently at a lower level, prior to object recognition itself. Multidimensional signal detection theory offers a useful framework, allowing us to model this as a low-level correlation between the internal noise distributions of viewpoint and object property dimensions. In Experiment 1, we measured these correlations using both Yes/No and adjustment tasks. We found a good correspondence across tasks, but large individual differences. In Experiment 2, we compared these results to the viewpoint dependence of object recognition through a Yes/No categorization task. We found that viewpoint-independent object recognition could not be fully reached using our stimuli, and that the pattern of viewpoint dependence was strongly correlated with the low-level correlations we measured earlier. In part, however, the viewpoint was abstracted despite these correlations. We conclude that low-level correlations do exist prior to object recognition, and can offer an explanation for some viewpoint effects on the discrimination of metrically manipulated 3-D objects.     

Are there geniuses among the apes?

We are often asked whether some apes are smarter than others. Here we used two individual-based datasets on cognitive abilities to answer this question and to elucidate the structure of individual differences. We identified some individuals who consistently scored well across multiple tasks, and even one individual who could be classified as exceptional when compared with her conspecifics. However, we found no general intelligence factor. Instead, we detected some clusters of certain abilities, including inferences, learning and perhaps a tool-use and quantities cluster. Thus, apes in general and chimpanzees in particular present a pattern characterized by the existence of some smart animals but no evidence of a general intelligence factor. This conclusion contrasts with previous studies that have found evidence of a g factor in primates. However, those studies have used group-based as opposed to the individual-based data used here, which means that the two sets of analyses are not directly comparable. We advocate an approach based on testing multiple individuals (of multiple species) on multiple tasks that capture cognitive, motivational and temperament factors affecting performance. One of the advantages of this approach is that it may contribute to reconcile the general and domain-specific views on primate intelligence.     

Behavioral and functional strategies during tool use tasks in bonobos

Different primate species have developed extensive capacities for grasping and manipulating objects. However, the manual abilities of primates remain poorly known from a dynamic point of view. The aim of the present study was to quantify the functional and behavioral strategies used by captive bonobos (Pan paniscus) during tool use tasks. The study was conducted on eight captive bonobos which we observed during two tool use tasks: food extraction from a large piece of wood and food recovery from a maze. We focused on grasping postures, in‐hand movements, the sequences of grasp postures used that have not been studied in bonobos, and the kind of tools selected. Bonobos used a great variety of grasping postures during both tool use tasks. They were capable of in‐hand movement, demonstrated complex sequences of contacts, and showed more dynamic manipulation during the maze task than during the extraction task. They arrived on the location of the task with the tool already modified and used different kinds of tools according to the task. We also observed individual manual strategies. Bonobos were thus able to develop in‐hand movements similar to humans and chimpanzees, demonstrated dynamic manipulation, and they responded to task constraints by selecting and modifying tools appropriately, usually before they started the tasks. These results show the necessity to quantify object manipulation in different species to better understand their real manual specificities, which is essential to reconstruct the evolution of primate manual abilities.     

Percent lipid is associated with body size but not task in the bumble bee <Emphasis Type="Italic">Bombus impatiens</Emphasis>

In some group-living organisms, labor is divided among individuals. This allocation to particular tasks is frequently stable and predicted by individual physiology. Social insects are excellent model organisms in which to investigate the interplay between physiology and individual behavior, as division of labor is an important feature within colonies, and individual physiology varies among the highly related individuals of the colony. Previous studies have investigated what factors are important in determining how likely an individual is, compared to nestmates, to perform certain tasks. One such task is foraging. Corpulence (i.e., percent lipid) has been shown to determine foraging propensity in honey bees and ants, with leaner individuals being more likely to be foragers. Is this a general trend across all social insects? Here we report data analyzing the individual physiology, specifically the percent lipid, of worker bumble bees (Bombus impatiens) from whom we also analyze behavioral task data. Bumble bees are also unusual among the social bees in that workers may vary widely in size. Surprisingly we find that, unlike other social insects, percent lipid is not associated with task propensity. Rather, body size closely predicts individual relative lipid stores, with smaller worker bees being allometrically fatter than larger worker bees.     

Ravens judge competitors through experience with play caching

Complex social behavior builds on the mutual judgment of individuals as cooperation partners and competitors [1]. Play can be used for assessing the others' dispositions in humans and nonhuman mammals [2], whereas little is known about birds. Recently, food-caching corvids have been found to rival primates in their ability to judge the behaviors and intentions of others in competition for hidden food [3]. Here, we show that ravens Corvus corax quickly learn to assess the competitive strategies of unfamiliar individuals through interactions with them over caches with inedible items and subsequently apply this knowledge when caching food. We confronted birds with two human experimenters who acted differently when birds cached plastic items: the pilferer stole the cached objects, whereas the onlooker did not. Birds responded to the actions of both experimenters with changing the location of their next object caches, either away from or toward the humans, as if they were testing their pilfering dispositions. In contrast, ravens instantly modified their caching behavior with food, preventing only the competitive human from finding the caches. Playful object caching in a social setting could thus aid ravens in evaluating others' pilfering skills.