Stimulus learning and response learning by observation in the European starling, in a two-object/two-action test

Global invasion history and native decline of the common starling: insights through genetics

Few invasive birds are as globally successful as the Common or European Starling (Sturnus vulgaris). Native to the Palearctic, the starling has been intentionally introduced to North and South America, South Africa, Australia, and the Pacific Islands, enabling us to explore species traits that may contribute to its invasion success. Coupling the rich studies of life history and more recent explorations of genomic variation among invasions, we illustrate how eco-evolutionary dynamics shape the invasion success of this long-studied and widely distributed species. Especially informative is the comparison between Australian and North American invasions, because these populations colonized novel ranges concurrently and exhibit shared signals of selection despite distinct population histories. In this review, we describe population dynamics across the native and invasive ranges, identify putatively selected traits that may influence the starling’s spread, and suggest possible determinants of starling success world-wide. We also identify future opportunities to utilize this species as a model for avian invasion research, which will inform our understanding of species’ rapid evolution in response to environmental change.

The effects of distance on pointing comprehension in shelter dogs

The Object Choice Task is a methodology that has been increasingly popular for several decades and many strong claims have been made regarding the differential results between species. However, many studies use differing methodologies and individuals with systematically different backgrounds, which makes any comparisons suspect. One of the methodological differences that has been shown to result in differing responses is distance, both between the objects, and between the object and the gesture. Here, we systematically test these differences with a sample of shelter dogs and note the potential mechanisms underlying the results. Dogs were more successful if the objects were further apart (Distal Object) or the point was very close to the object (Proximal Cue). Success in both of these conditions can be most parsimoniously explained by mechanistic strategies, i.e. strategies that do not rely on mental representation or communicative mechanisms. We also note the results of some pilot data suggesting a non-communicative mechanism (body alignment through touch) by which shelter dogs and other animals may successfully respond when the objects and gestures are distant. We argue that the only point type that likely relies on communicative mechanisms is when the objects are close together, but the point is distant the condition in which dogs are least successful. Future research should take into consideration that individual dogs may use different strategies, or may switch between strategies, and note that all point-following is not necessarily indicative of communicative comprehension.

Chronic stress reverses enhanced neophobia following an acute stressor in European starlings

Neophobia is an animal's avoidance of novelty. Animals tend to respond to novel objects by increasing their latency to approach the objects, and they eventually habituate after repeated exposure by attenuating this increased approach latency. Interestingly, the physiological stress response does not appear to have a causal link to neophobia, although acute stress can prevent animals from habituating to novel objects, possibly through a permissive effect. Chronic stress can induce an anxiety-like state in animals, while often disrupting the ability to respond to acute stress. We thus hypothesized that chronic stress may increase neophobia and tested this by inducing chronic stress in wild-caught European starlings (Sturnus vulgaris). Four distinct anthropogenic stressors were administered daily for 30 min each in a randomized order for 21 days. We then evaluated whether exposure to chronic stress altered the latency to approach a novel object placed on or near a food dish presented after overnight fasting. Chronically stressed birds and nonstressed controls exhibited similar initial neophobic responses to novel objects and showed similar habituation in response to repeated exposure. However, when birds were exposed to 15 min of restraint before repeated exposure to the same object, habituation was eliminated in control birds (i.e., they continued to respond with neophobia), whereas chronically stressed birds continued to show habituation as measured by attenuated approach latencies. These results demonstrate that an acute stress response (restraint) has a different impact on neophobia depending upon whether the bird is or is not concurrently exposed to chronic stress.

Social learning through associative processes: a computational theory

Social transmission of information is a key phenomenon in the evolution of behaviour and in the establishment of traditions and culture. The diversity of social learning phenomena has engendered a diverse terminology and numerous ideas about underlying learning mechanisms, at the same time that some researchers have called for a unitary analysis of social learning in terms of associative processes. Leveraging previous attempts and a recent computational formulation of associative learning, we analyse the following learning scenarios in some generality: learning responses to social stimuli, including learning to imitate; learning responses to non-social stimuli; learning sequences of actions; learning to avoid danger. We conceptualize social learning as situations in which stimuli that arise from other individuals have an important role in learning. This role is supported by genetic predispositions that either cause responses to social stimuli or enable social stimuli to reinforce specific responses. Simulations were performed using a new learning simulator program. The simulator is publicly available and can be used for further theoretical investigations and to guide empirical research of learning and behaviour. Our explorations show that, when guided by genetic predispositions, associative processes can give rise to a wide variety of social learning phenomena, such as stimulus and local enhancement, contextual imitation and simple production imitation, observational conditioning, and social and response facilitation. In addition, we clarify how associative mechanisms can result in transfer of information and behaviour from experienced to naive individuals.

Diffusion of novel foraging behaviour in Amazon parrots through social learning

While social learning has been demonstrated in species across many taxa, the role it plays in everyday foraging decisions is not well understood. Investigating social learning during foraging could shed light on the emergence of cultural variation in different groups. We used an open diffusion experiment to examine the spread of a novel foraging technique in captive Amazon parrots. Three groups were tested using a two-action foraging box, including experimental groups exposed to demonstrators using different techniques and control birds. We also examined the influence of agonistic and pilfering behaviour on task acquisition. We found evidence of social learning: more experimental birds than control birds interacted with and opened the box. The birds were, however, no more likely to use the demonstrated technique than the non-demonstrated one, making local or stimulus enhancement the most likely mechanism. Exhibiting aggression was positively correlated with box opening, whilst receiving aggression did not reduce motivation to engage with the box, indicating that willingness to defend access to the box was important in task acquisition. Pilfering food and success in opening the box were also positively correlated; however, having food pilfered did not affect victims' motivation to interact with the box. In a group context, pilfering may promote learning of new foraging opportunities. Although previous studies have demonstrated that psittacines are capable of imitation, in this naturalistic set-up there was no evidence that parrots copied the demonstrated opening technique. Foraging behaviour in wild populations of Amazons could therefore be facilitated by low-fidelity social learning mechanisms.

Learning by observation in the macaque monkey under high experimental constraints

While neuroscience research has tremendously advanced our knowledge about the neural mechanisms of individual learning, i.e. through trial-and-error, it is only recently that neuroscientists have begun to study observational learning, and thus little is known about its neural mechanisms. One limitation is that observational learning has been addressed under unconstrained experimental conditions, not compatible with neuronal recordings. This study examined observational learning in macaque monkeys under the constraining conditions of behavioral neurophysiology. Two animals sat in primate chairs facing each other, with their head fixed. A touch screen was placed face up between the chairs at arm's reach, and the monkeys were trained on an abstract visuomotor associative task. In one experiment, the monkeys alternated the roles of "actor" and "observer". The actor learned to associate visual cues with reaching targets, while the observer "watched" freely. Then, the observer was given the same cue-target associations just performed by the actor, or had to learn new, not previously observed ones. The results show that learning performance is better after observation. In experiment 2, one monkey learned from a human actor who performed the task with errors only, or with successes only in separate blocks. The monkey's gain in performance was higher after observation of errors than after successes. The findings suggest that observational learning can occur even under highly constraining conditions, and open the way for investigating the neuronal correlates of social learning using the methods of behavioral neurophysiology.

Memory, transmission and persistence of alternative foraging techniques in wild common marmosets

Experimental studies on traditions in animals have focused almost entirely on the initial transmission phase in captive populations. We conducted an open diffusion field experiment with 13 groups of wild common marmosets, Callithrix jacchus. Seven groups contained individuals that were already familiar with the task (‘push or pull’ box) and thus served as potential models for naïve individuals. Additionally, in four groups one individual was trained for one of the two possible techniques and in two control groups no skilled individuals were present. First, we investigated whether experienced individuals would remember how to solve the task even after 2 years without exposure and whether they would still prefer their learned technique. Second, we tested whether naïve individuals would learn socially from their skilled family members and, more importantly, whether they would use the same technique. Third, we conducted several test blocks to see whether the individual and/or group behaviour would persist over time. Our results show that wild common marmosets were able to memorize, learn socially and maintain preferences of foraging techniques. This field experiment thus reveals a promising approach to studying social learning in the wild and provides the basis for long-term studies on tradition formation.

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We show all key components of behavioural traditions in free-living primates.

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Wild marmosets maintained a foraging technique for over 2 years without exposure.

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Naïve individuals adopted the technique from their skilled family members.

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They preserved their learned foraging variants for at least 9 months.

When rank counts — dominant dogs learn better from a human demonstrator in a two-action test

Abstract

Dogs can learn effectively from a human demonstrator in detour tests as well as in different kinds of manipulative tasks. In this experiment we used a novel two-action device from which the target object (a ball) was obtained by tilting a tube either by pulling a rope attached to the end of the tube, or by directly pushing the end of the tube. Tube tilting was relatively easy for naïve companion dogs; therefore, the effect of the human demonstration aimed to alter or increase the dogs’ initial preference for tube pushing (according to the behaviour shown by naïve dogs in the absence of a human demonstrator). Our results have shown that subjects preferred the demonstrated action in the two-action test. After having witnessed the tube pushing demonstration, dogs performed significantly more tube pushing than the dogs in the rope pulling demonstration group. In contrast, dogs that observed the rope pulling demonstration, performed significantly more similar actions than the subjects of the other demonstration group. The ratio of rope pulling was significantly higher in the rope pulling demonstration group, than in the No Demo (control) group. The overall success of solving the task was also influenced by the social rank of the dog among its conspecific companions at home. Independently of the type of demonstration, dominant dogs solved the task significantly more often than the subordinate dogs did. There was no such difference in the No Demo group.

This experiment has shown that a simple two-action device that does not require excessive pre-training, can be suitable for testing social learning in dogs. However, effects of social rank should be taken into account when social learning in dogs is being studied and tested, because dominant and subordinate dogs perform differently after observing a demonstrator.

Associative sequence learning: the role of experience in the development of imitation and the mirror system

A core requirement for imitation is a capacity to solve the correspondence problem; to map observed onto executed actions, even when observation and execution yield sensory inputs in different modalities and coordinate frames. Until recently, it was assumed that the human capacity to solve the correspondence problem is innate. However, it is now becoming apparent that, as predicted by the associative sequence learning model, experience, and especially sensorimotor experience, plays a critical role in the development of imitation. We review evidence from studies of non-human animals, children and adults, focusing on research in cognitive neuroscience that uses training and naturally occurring variations in expertise to examine the role of experience in the formation of the mirror system. The relevance of this research depends on the widely held assumption that the mirror system plays a causal role in generating imitative behaviour. We also report original data supporting this assumption. These data show that theta-burst transcranial magnetic stimulation of the inferior frontal gyrus, a classical mirror system area, disrupts automatic imitation of finger movements. We discuss the implications of the evidence reviewed for the evolution, development and intentional control of imitation.

Animal consciousness: a synthetic approach

Despite anecdotal evidence suggesting conscious states in a variety of non-human animals, no systematic neuroscientific investigation of animal consciousness has yet been undertaken. We set forth a framework for such an investigation that incorporates integration of data from neuroanatomy, neurophysiology, and behavioral studies, uses evidence from humans as a benchmark, and recognizes the critical role of explicit verbal report of conscious experiences in human studies. We illustrate our framework with reference to two subphyla: one relatively near to mammals - birds - and one quite far -cephalopod molluscs. Consistent with the possibility of conscious states, both subphyla exhibit complex behavior and possess sophisticated nervous systems. Their further investigation may reveal common phyletic conditions and neural substrates underlying the emergence of animal consciousness.

Subtle cues of predation risk: starlings respond to a predator's direction of eye-gaze

For prey animals to negotiate successfully the fundamental trade-off between predation and starvation, a realistic assessment of predation risk is vital. Prey responses to conspicuous indicators of risk (such as looming predators or fleeing conspecifics) are well documented, but there should also be strong selection for the detection of more subtle cues. A predator's head orientation and eye-gaze direction are good candidates for subtle but useful indicators of risk, since many predators orient their head and eyes towards their prey as they attack. We describe the first explicit demonstration of a bird responding to a live predator's eye-gaze direction. We present wild-caught European starlings (Sturnus vulgaris) with human 'predators' whose frontal appearance and gaze direction are manipulated independently, and show that starlings are sensitive to the predator's orientation, the presence of eyes and the direction of eye-gaze. Starlings respond in a functionally significant manner: when the predator's gaze was averted, starlings resumed feeding earlier, at a higher rate and consumed more food overall. By correctly assessing lower risk and returning to feeding activity earlier (as in this study), the animal gains a competitive advantage over conspecifics that do not respond to the subtle predator cue in this way.

Social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens) on a two-action artificial fruit

An artificial fruit (AF) was used to test for social learning in pig-tailed macaques (Macaca nemestrina) and adult humans (Homo sapiens). A monkey demonstrator opened the AF, showing alternative methods to 2 groups of cage mates. Video films of the monkey demonstrations were presented to adult humans. Compared with chimpanzees and children, the macaques watched the demonstrations significantly less and in a much more sporadic manner. They also produced only very weak and transitory evidence of social learning. In contrast, the adult humans performed as one might expect of optimum imitators, even producing evidence of components of a "ratchet effect."

Testing for localized stimulus enhancement and object movement reenactment in pig-tailed macaques (Macaca nemestrina) and young children (Homo sapiens)

Four puzzle boxes were used to investigate localized stimulus enhancement and object movement reenactment (OMR) in 13 pig-tailed macaques (Macaca nemestrina) and 30 human infants (Homo sapiens). Participants received contrasting demonstrations on each box. A circular lid was gripped by its rim or handle and swiveled to the left or right. A flap door was pushed or flipped. A sliding lid was pushed to the left or right. A pin bolt was demonstrated being pushed down, or the participants were left to solve the puzzle for themselves. Despite the fact that the monkeys watched the demonstrations about 60% of the time, only a weak OMR effect was found on the sliding lid. In contrast, the children watched significantly more, and there was clear evidence of socially mediated learning on all of the boxes.

Cognitive ornithology: the evolution of avian intelligence

Comparative psychologists interested in the evolution of intelligence have focused their attention on social primates, whereas birds tend to be used as models of associative learning. However, corvids and parrots, which have forebrains relatively the same size as apes, live in complex social groups and have a long developmental period before becoming independent, have demonstrated ape-like intelligence. Although, ornithologists have documented thousands of hours observing birds in their natural habitat, they have focused their attention on avian behaviour and ecology, rather than intelligence. This review discusses recent studies of avian cognition contrasting two different approaches; the anthropocentric approach and the adaptive specialization approach. It is argued that the most productive method is to combine the two approaches. This is discussed with respects to recent investigations of two supposedly unique aspects of human cognition; episodic memory and theory of mind. In reviewing the evidence for avian intelligence, corvids and parrots appear to be cognitively superior to other birds and in many cases even apes. This suggests that complex cognition has evolved in species with very different brains through a process of convergent evolution rather than shared ancestry, although the notion that birds and mammals may share common neural connectivity patterns is discussed.

Imitative learning of stimulus-response and response-outcome associations in pigeons

A novel automated procedure was used to study imitative learning in pigeons. In Experiments 1 and 2, observer pigeons witnessed a demonstrator pigeon successfully performing an instrumental discrimination in which different discriminative stimuli indicated which of 2 topographically distinct responses (R1 and R2) resulted in the delivery of seed. The observers were then presented with the discriminative stimuli and given access to the response panel. Observer pigeons' behavior during the discriminative stimuli was influenced by how the demonstrator had responded during these stimuli. In Experiment 3, observers witnessed demonstrator pigeons performing R1 for Outcome 1 and R2 for Outcome 2. Observers then received a procedure designed to devalue Outcome 1 relative to Outcome 2 and were subsequently less likely to perform R1 than R2. These results suggest that pigeons can learn both stimulus response and response-outcome associations by observation.

Socially learned preferences for differentially rewarded tokens in the brown capuchin monkey (Cebus apella)

Social learning is assumed to underlie traditions, yet evidence indicating social learning in capuchin monkeys (Cebus apella), which exhibit traditions, is sparse. The authors tested capuchins for their ability to learn the value of novel tokens using a previously familiar token-exchange economy. Capuchins change their preferences in favor of a token worth a high-value food reward after watching a conspecific model exchange 2 differentially rewarded tokens, yet they fail to develop a similar preference after watching tokens paired with foods in the absence of a conspecific model. They also fail to learn that the value of familiar tokens has changed. Information about token value is available in all situations, but capuchins seem to pay more attention in a social situation involving novel tokens.

Preference for copying unambiguous demonstrations in dogs (Canis familiaris)

In an earlier study (P. Pongracz et al., 2001), it was shown that human demonstration significantly enhances the detouring ability of dogs (Canis familiaris) around a V-shaped fence. The authors investigated the effect of the direction of the demonstrated detour and the dogs' detouring experience. They found that dogs' trial-and-error experience influences strongly the direction of the dogs' detours later, even if the demonstrator showed detours along the opposite side of the fence. However, dogs' preferences based on their own experiences were changed when the dogs observed demonstrations only on 1 side of the fence. Dogs with no trial-and-error experience followed the direction of 1-sided demonstrations. The change from dogs' own directions to the demonstrated directions seems not to be due to simple facilitative effects of social experience; the similarity with the demonstrated action depends on complex interactions between individual experience and socially provided information.

How do apes ape?

In the wake of telling critiques of the foundations on which earlier conclusions were based, the last 15 years have witnessed a renaissance in the study of social learning in apes. As a result, we are able to review 31 experimental studies from this period in which social learning in chimpanzees, gorillas, and orangutans has been investigated. The principal question framed at the beginning of this era, Do apes ape? has been answered in the affirmative, at least in certain conditions. The more interesting question now is, thus, How do apes ape? Answering this question has engendered richer taxonomies of the range of social-learning processes at work and new methodologies to uncover them. Together, these studies suggest that apes ape by employing a portfolio of alternative social-learning processes in flexibly adaptive ways, in conjunction with nonsocial learning. We conclude by sketching the kind of decision tree that appears to underlie the deployment of these alternatives.

Action imitation in birds

Action imitation, once thought to be a behavior almost exclusively limited to humans and the great apes, surprisingly also has been found in a number of bird species. Because imitation has been viewed by some psychologists as a form of intelligent behavior, there has been interest in how it is distributed among animal species. Although the mechanisms responsible for action imitation are not clear, we are now at least beginning to understand the conditions under which it occurs. In this article, I try to identify and differentiate the various forms of socially influenced behavior (species-typical social reactions, social effects on motivation, social effects on perception, socially influenced learning, and action imitation) and explain why it is important to differentiate imitation from other forms of social influence. I also examine some of the variables that appear to be involved in the occurrence of imitation. Finally, I speculate about why a number of bird species, but few mammal species, appear to imitate.

Evolutionary model with genetics, aging, and knowledge

We represent a process of learning by using bit strings, where 1 bits represent the knowledge acquired by individuals. Two ways of learning are considered: individual learning by trial and error, and social learning by copying knowledge from other individuals or from parents in the case of species with parental care. The age-structured bit string allows us to study how knowledge is accumulated during life and its influence over the genetic pool of a population after many generations. We use the Penna model to represent the genetic inheritance of each individual. In order to study how the accumulated knowledge influences the survival process, we include it to help individuals to avoid the various death situations. Modifications in the Verhulst factor do not show any special feature due to its random nature. However, by adding years to life as a function of the accumulated knowledge, we observe an improvement of the survival rates while the genetic fitness of the population becomes worse. In this latter case, knowledge becomes more important in the last years of life where individuals are threatened by diseases. Effects of offspring overprotection and differences between individual and social learning can also be observed. Sexual selection as a function of knowledge shows some effects when fidelity is imposed.

Verbal Attention Getting as a Key Factor in Social Learning Between Dog (Canis familiaris) and Human

Pet dogs (Canis familiaris) learn to detour a V-shaped fence effectively from an unfamiliar human demonstrator. In this article, 4 main features of the demonstrator's behavior are highlighted: (a) the manipulation of the target, (b) the familiarity of the demonstrator, (c) the role of verbal attention-getting behavior, and (d) whether a strange trained dog could also be an effective demonstrator. The results show that the main factor of a successful human demonstration is the continuous verbal communication with the dog during detouring. It was also found that an unfamiliar dog demonstrator was as efficient as the unfamiliar experimenter. The experiments provide evidence that in adult dogs, communicative context with humans is needed for effective interspecific social learning to take place.

Social influence in pigeons (Columba livia): the role of differential reinforcement

Socially-influenced learning was studied in observer pigeons that observed a demonstrator in an adjacent chamber performing a target response comprising standing on a box and pecking a key 10 times. In Experiment 1 there was no evidence for social learning in the absence of reinforcement of the observer's behavior. When the target response was already established in the observer's repertoire, but was not differentially reinforced in relation to the demonstrator's behavior, rates of extinction were not influenced by the demonstrator's behavior (Experiment 2). Reinforcement of the observer's target response in the presence of the modeled target response, and not in its absence, resulted in control of the observer's responding by the behavior of the demonstrator (Experiments 3 and 4). This control was extended in Experiment 5 to deferred responses that occurred following a delay since the demonstrator's target responses. The acquisition of social influence depended on differential reinforcement of the observer's target response, with the demonstrator's target behavior serving as the explicit discriminative stimulus.

Budgerigars (Melopsittacus undulatus) Copy Virtual Demonstrators in a Two-Action Test

Juvenile budgerigars (Melopsittacus undulatus) observed thin film transistor video playback of a virtual conspecific demonstrator using its beak to remove a stopper from a food box, either by pulling the object upward or by pushing it downward. Simultaneously (Experiment 1) or subsequently (Experiment 2), the observers were offered a similar stopper box and rewarded with access to food for each removal response, regardless of its direction. Observers of upward movement made a greater proportion of up responses in total and showed a stronger tendency to increase the proportion of up responses over test trials than observers of downward movement. These findings provide the first demonstration of which the authors are aware that birds are able not only to detect and respond to a moving video image but also to copy its movements.

Four routes of cognitive evolution

Four routes of cognitive evolution are distinguished: phylogenetic construction, in which natural selection produces qualitative change to the way a cognitive mechanism operates (language); phylogenetic inflection, in which natural selection biases the input to a cognitive mechanism (imprinting and spatial memory); ontogenetic construction, in which developmental selection alters the way a cognitive mechanism operates (face recognition and theory of mind); and ontogenetic inflection, in which developmental selection changes the input to a cognitive mechanism (imitation). This framework integrates findings from evolutionary psychology (i.e., all research on the evolution of mentality and behavior). In contrast with human nativist evolutionary psychology, it recognizes the adaptive significance of developmental processes, conserves the distinction between cognitive and noncognitive mechanisms, and encompasses research on human and nonhuman animals.

Imitative learning in Japanese quail (Coturnix japonica) using the bidirectional control procedure

In the bidirectional control procedure, observers are exposed to a conspecific demonstrator responding to a manipulandum in one of two directions (e.g., left vs. right). This procedure controls for socially mediated effects (the mere presence of a conspecific) and stimulus enhancement (attention drawn to a manipulandum by its movement), and it has the added advantage of being symmetrical (the two different responses are similar in topography). Imitative learning is demonstrated when the observers make the response in the direction that they observed it being made. Recently, however, it has been suggested that when such evidence is found with a predominantly olfactory animal, such as the rat, it may result artifactually from odor cues left on one side of the manipulandum by the demonstrator. In the present experiment, we found that Japanese quail, for which odor cues are not likely to play a role, also showed significant correspondence between the direction in which the demonstrator and the observer push a screen to gain access to reward. Furthermore, control quail that observed the screen move, when the movement of the screen was not produced by the demonstrator, did not show similar correspondence between the direction of screen movement observed and that performed by the observer. Thus, with the appropriate control, the bidirectional procedure appears to be useful for studying imitation in avian species.

Imitative learning in Japanese quail (Coturnix japonica) depends on the motivational state of the observer quail at the time of observation

The 2-action method was used to examine whether imitative learning in Japanese quail (Coturnix japonica) depends on the motivational state of the observer quail at the time of observation of the demonstrated behavior. Two groups of observers were fed before observation (satiated groups), whereas 2 other groups of observers were deprived of food before observation (hungry groups). Quail were tested either immediately following observation or after a 30-min delay. Results indicated that quail in the hungry groups imitated, whereas those in the satiated groups did not, regardless of whether their test was immediate or delayed. The results suggest that observer quail may not learn (through observation) behavior that leads to a reinforcer for which they are unmotivated at the time of test. In addition, the results show that quail are able to delay the performance of a response acquired through observation (i.e., they show deferred imitation).

Social influences on foraging in vertebrates: causal mechanisms and adaptive functions

We summarize 20 years of empirical and theoretical research on causes and functions of social influences on foraging by animals. We consider separately studies of social influence on when, where, what and how to eat. Implicit in discussion of the majority of studies is our assumption that social influences on foraging reflect a biasing of individual learning processes by social stimuli rather than action of independent social-learning mechanisms. Our review of theoretical approaches suggests that the majority of formally derived hypotheses concerning functions of social influence on foraging have not yet been tested adequately and many models are in need of further refinement. We also consider the importance to the future of the field of integrating 'top-down' and 'bottom-up' approaches to the study of social learning. Copyright 2001 The Association for the Study of Animal Behaviour.

True imitation in marmosets

Marmosets, Callithrix jacchus, observed a demonstrator removing the lids from a series of plastic canisters to obtain a mealworm. When subsequently allowed access to the canisters, marmosets that observed a demonstrator using its hands to remove the lids used only their hands. In contrast, marmosets that observed a demonstrator using its mouth also used their mouth to remove the lids. Since hand and mouth demonstrators brought about identical changes in the canisters, the differential test behaviour of the observer groups suggests that they learned about the demonstrator's behaviour. Furthermore, marmosets that had not been given the opportunity to observe a demonstrator prior to testing had a low probability of mouth opening, even if the canisters were previously opened by a mouth-opening demonstrator in an olfactory control experiment. Corroborating Bugnyar & Huber's (1997, Animal Behaviour, 54, 817-831) earlier findings, our results provide further evidence that marmosets can imitate. Copyright 2000 The Association for the Study of Animal Behaviour.