Serial reversal learning in nectar-feeding bats

We explored the behavioral flexibility of Commissaris's long-tongued bats through a spatial serial reversal foraging task. Bats kept in captivity for short periods were trained to obtain nectar rewards from two artificial flowers. At any given time, only one of the flowers provided rewards and these reward contingencies reversed in successive blocks of 50 flower visits. All bats detected and responded to reversals by making most of their visits to the currently active flower. As the bats experienced repeated reversals, their preference re-adjusted faster. Although the flower state reversals were theoretically predictable, we did not detect anticipatory behavior, that is, frequency of visits to the alternative flower did not increase within each block as the programmed reversal approached. The net balance of these changes was a progressive improvement in performance in terms of the total proportion of visits allocated to the active flower. The results are compatible with, but do not depend on, the bats displaying an ability to 'learn to learn' and show that the dynamics of allocation of effort between food sources can change flexibly according to circumstances.

GoFish: A low-cost, open-source platform for closed-loop behavioural experiments on fish

Fish are the most species-rich vertebrate group, displaying vast ecological, anatomical and behavioural diversity, and therefore are of major interest for the study of behaviour and its evolution. However, with respect to other vertebrates, fish are relatively underrepresented in psychological and cognitive research. A greater availability of easily accessible, flexible, open-source experimental platforms that facilitate the automation of task control and data acquisition may help to reduce this bias and improve the scalability and refinement of behavioural experiments in a range of different fish species. Here we present GoFish, a fully automated platform for behavioural experiments in aquatic species. GoFish includes real-time video tracking of subjects, presentation of stimuli in a computer screen, an automatic feeder device, and closed-loop control of task contingencies and data acquisition. The design and software components of the platform are freely available, while the hardware is open-source and relatively inexpensive. The control software, Bonsai, is designed to facilitate rapid development of task workflows and is supported by a growing community of users. As an illustration and test of its use, we present the results of two experiments on discrimination learning, reversal, and choice in goldfish (Carassius auratus). GoFish facilitates the automation of high-throughput protocols and the acquisition of rich behavioural data. Our platform has the potential to become a widely used tool that facilitates complex behavioural experiments in aquatic species.

Paradoxical choice and the reinforcing value of information

Signals that reduce uncertainty can be valuable because well-informed decision-makers can better align their preferences to opportunities. However, some birds and mammals display an appetite for informative signals that cannot be used to increase returns. We explore the role that reward-predictive stimuli have in fostering such preferences, aiming at distinguishing between two putative underlying mechanisms. The 'information hypothesis' proposes that reducing uncertainty is reinforcing per se, somewhat consistently with the concept of curiosity: a motivation to know in the absence of tractable extrinsic benefits. In contrast, the 'conditioned reinforcement hypothesis', an associative account, proposes asymmetries in secondarily acquired reinforcement: post-choice stimuli announcing forthcoming rewards (S⁺) reinforce responses more than stimuli signalling no rewards (S^-) inhibit responses. In three treatments, rats faced two equally profitable options delivering food probabilistically after a fixed delay. In the informative option (Info), food or no food was signalled immediately after choice, whereas in the non-informative option (NoInfo) outcomes were uncertain until the delay lapsed. Subjects preferred Info when (1) both outcomes were explicitly signalled by salient auditory cues, (2) only forthcoming food delivery was explicitly signalled, and (3) only the absence of forthcoming reward was explicitly signalled. Acquisition was slower in (3), when food was not explicitly signalled, showing that signals for positive outcomes have a greater influence on the development of preference than signals for negative ones. Our results are consistent with an elaborated conditioned reinforcement account, and with the conjecture that both uncertainty reduction and conditioned reinforcement jointly act to generate preference.

Imprinting on time-structured acoustic stimuli in ducklings

Filial imprinting is a dedicated learning process that lacks explicit reinforcement. The phenomenon itself is narrowly heritably canalized, but its content, the representation of the parental object, reflects the circumstances of the newborn. Imprinting has recently been shown to be even more subtle and complex than previously envisaged, since ducklings and chicks are now known to select and represent for later generalization abstract conceptual properties of the objects they perceive as neonates, including movement pattern, heterogeneity and inter-component relationships of same or different. Here, we investigate day-old Mallard (Anas platyrhynchos) ducklings' bias towards imprinting on acoustic stimuli made from mallards' vocalizations as opposed to white noise, whether they imprint on the temporal structure of brief acoustic stimuli of either kind, and whether they generalize timing information across the two sounds. Our data are consistent with a strong innate preference for natural sounds, but do not reliably establish sensitivity to temporal relations. This fits with the view that imprinting includes the establishment of representations of both primary percepts and selective abstract properties of their early perceptual input, meshing together genetically transmitted prior pre-dispositions with active selection and processing of the perceptual input.

Sex differences in the use of spatial cues in two avian brood parasites

Shiny and screaming cowbirds are avian interspecific brood parasites that locate and prospect host nests in daylight and return from one to several days later to lay an egg during the pre-dawn twilight. Thus, during nest location and prospecting, both location information and visual features are available, but the latter become less salient in the low-light conditions when the nests are visited for laying. This raises the question of how these different sources of information interact, and whether this reflects different behavioural specializations across sexes. Differences are expected, because in shiny cowbirds, females act alone, but in screaming cowbirds, both sexes make exploratory and laying nest visits together. We trained females and males of shiny and screaming cowbird to locate a food source signalled by both colour and position (cues associated), and evaluated performance after displacing the colour cue to make it misleading (cues dissociated). There were no sex or species differences in acquisition performance while the cues were associated. When the colour cue was relocated, individuals of both sexes and species located the food source making fewer visits to non-baited wells than expected by chance, indicating that they all retained the position as an informative cue. In this phase, however, shiny cowbird females, but not screaming, outperformed conspecific males, visiting fewer non-baited wells before finding the food location and making straighter paths in the search. These results are consistent with a greater reliance on spatial memory, as expected from the shiny cowbird female's specialization on nest location behaviour.

Choosing fast and simply: Construction of preferences by starlings through parallel option valuation

The integration of normative and descriptive analyses of decision processes in humans struggles with the fact that measuring preferences by different procedures yields different rankings and that humans appear irrationally impulsive (namely, show maladaptive preference for immediacy). Failure of procedure invariance has led to the widespread hypothesis that preferences are constructed "on the spot" by cognitive evaluations performed at choice time, implying that choices should take extra time in order to perform the necessary comparisons. We examine this issue in experiments with starlings (Sturnus vulgaris) and show that integrating normative and descriptive arguments is possible and may help reinterpreting human decision results. Our main findings are that (1) ranking alternatives through direct rating (response time) accurately predicts preference in choice, overcoming failures of procedure invariance; (2) preference is not constructed at choice time nor does it involve extra time (we show that the opposite is true); and (3) starlings' choices are not irrationally impulsive but are instead directly interpretable in terms of profitability ranking. Like all nonhuman research, our protocols examine decisions by experience rather than by description, and hence support the conjecture that irrationalities that prevail in research with humans may not be observed in decisions by experience protocols.

Ducklings imprint on chromatic heterogeneity

Avian filial imprinting is a rapid form of learning occurring just after hatching in precocial bird species. The acquired imprint on either or both parents goes on to affect the young bird's survival and social behaviour later in life (Bateson in Biol Rev 41:177-217, 1966). The imprinting mechanism is specialized but flexible, and causes the hatchling to develop high-fidelity recognition and attraction to any moving stimulus of suitable size seen during a predefined sensitive period. It has been observed (Martinho and Kacelnik in Science 353:286-288, 2016; Versace et al. in Anim Cogn 20:521-529, 2017) that in addition to visual and acoustic sensory inputs, imprinting may incorporate informational rules or abstract concepts. Here we report a study of mallard ducklings (Anas platyrhynchos domesticus) undergoing imprinting on the chromatic heterogeneity of stimuli, with a focus on how this may be transferred to novel objects. Ducklings were exposed to a series of chromatically heterogeneous or homogeneous stimuli and tested for preference between two novel stimuli, one heterogeneous and the other homogeneous. Exposure to heterogeneity significantly enhanced preference for novel heterogeneous stimuli, relative to ducklings exposed to homogeneous stimuli or unexposed controls. These findings support the view that imprinting does not rely solely on exemplars, or snapshot-like representations of visual input, but that instead young precocial animals form complex multidimensional representations of the target object, involving abstract properties, either at the time of learning, or later, through generalization from the learnt exemplars.

Compound tool construction by New Caledonian crows

The construction of novel compound tools through assemblage of otherwise non-functional elements involves anticipation of the affordances of the tools to be built. Except for few observations in captive great apes, compound tool construction is unknown outside humans, and tool innovation appears late in human ontogeny. We report that habitually tool-using New Caledonian crows (Corvus moneduloides) can combine objects to construct novel compound tools. We presented 8 naïve crows with combinable elements too short to retrieve food targets. Four crows spontaneously combined elements to make functional tools, and did so conditionally on the position of food. One of them made 3- and 4-piece tools when required. In humans, individual innovation in compound tool construction is often claimed to be evolutionarily and mechanistically related to planning, complex task coordination, executive control, and even language. Our results are not accountable by direct reinforcement learning but corroborate that these crows possess highly flexible abilities that allow them to solve novel problems rapidly. The underlying cognitive processes however remain opaque for now. They probably include the species' typical propensity to use tools, their ability to judge affordances that make some objects usable as tools, and an ability to innovate perhaps through virtual, cognitive simulations.

Maintaining performance in searching dogs: Evidence from a rat model that training to detect a second (irrelevant) stimulus can maintain search and detection responding

Scent-detecting dogs perform a sequence, or chain, of behaviors that, at minimum, includes searching followed by a detection behavior that signals the presence of a target stimulus to the handler. However, when working, dogs often engage in prolonged periods of searching without encountering a target. It is therefore important for trainers to use methods that promote persistent search behavior and target detection accuracy. Laboratory models can provide insights to the important variables that influence search persistence and accuracy. The present experiments examined a rat model of detection dog behavior. Two experiments assessed the use of practice with a single target stimulus to maintain search and detection of another previously-trained target. In Experiment 1, after learning a search→detection chain with two auditory targets, rats received either brief or extended training with only one of the targets before being tested for detection of both targets in extinction. The results suggest that single-target training strengthened the ability of the other target to control the detection behavior. Experiment 2 found that even infrequent target encounters were still effective at maintaining detection behavior to the other trained target. Importantly, the treatment was effective when the target stimuli were from different sensory modalities. Overall, the results support the utility of the rat model of search-dog behavior for evaluating novel training methods. We suggest several useful procedures for enhancing search persistence and accuracy in detection dogs that can be implemented in training protocols.

Parallel vs. comparative evaluation of alternative options by colonies and individuals of the ant Temnothorax rugatulus

Both a single ant and the colony to which it belongs can make decisions, but the underlying mechanisms may differ. Colonies are known to be less susceptible than lone ants to “choice overload”, whereby decision quality deteriorates with increasing number of options. We probed the basis of this difference, using the model system of nest-site selection by the ant Temnothorax rugatulus. We tested the applicability of two competing models originally developed to explain information-processing mechanisms in vertebrates. The Tug of War model states that concurrent alternatives are directly compared, so that choosing between two alternatives takes longer than accepting a single one. In contrast, the Sequential Choice Model assumes that options are examined in parallel, and action takes place once any option reaches a decision criterion, so that adding more options shortens time to act. We found that single ants matched the Tug of War model while colonies fitted the Sequential Choice model. Our study shows that algorithmic models for decision-making can serve to investigate vastly different domains, from vertebrate individuals to both individuals and colonies of social insects.

Priors in Animal and Artificial Intelligence: Where Does Learning Begin?

A major goal for the next generation of artificial intelligence (AI) is to build machines that are able to reason and cope with novel tasks, environments, and situations in a manner that approaches the abilities of animals. Evidence from precocial species suggests that driving learning through suitable priors can help to successfully face this challenge.

Paradoxical choice in rats: Subjective valuation and mechanism of choice

Decision-makers benefit from information only when they can use it to guide behavior. However, recent experiments found that pigeons and starlings value information that they cannot use. Here we show that this paradox is also present in rats, and explore the underlying decision process. Subjects chose between two options that delivered food probabilistically after a fixed delay. In one option ("info"), outcomes (food/no-food) were signaled immediately after choice, whereas in the alternative ("non-info") the outcome was uncertain until the delay lapsed. Rats sacrificed up to 20% potential rewards by preferring the info option, but reversed preference when the cost was 60%. This reversal contrasts with the results found with pigeons and starlings and may reflect species' differences worth of further investigation. Results are consistent with predictions of the Sequential Choice Model (SCM), that proposes that choices are driven by the mechanisms that control action in sequential encounters. As expected from the SCM, latencies to respond in single-option trials predicted preferences in choice trials, and latencies in choice trials were the same or shorter than in single-option trials. We argue that the congruence of results in distant vertebrates probably reflects evolved adaptations to shared fundamental challenges in nature, and that the apparently paradoxical overvaluing of information is not sub-optimal as has been claimed, even though its functional significance is not yet understood.

Goffin's cockatoos make the same tool type from different materials

Innovative tool manufacture is rare and hard to isolate in animals. We show that an Indonesian generalist parrot, the Goffin's cockatoo, can flexibly and spontaneously transfer the manufacture of stick-type tools across three different materials. Each material required different manipulation patterns, including substrates that required active sculpting for achieving a functional, elongated shape.

Adaptations to different habitats in sexual and asexual populations of parasitoid wasps: a meta-analysis

BACKGROUND

Coexistence of sexual and asexual populations remains a key question in evolutionary ecology. We address the question how an asexual and a sexual form of the parasitoid Venturia canescens can coexist in southern Europe. We test the hypothesis that both forms are adapted to different habitats within their area of distribution. Sexuals inhabit natural environments that are highly unpredictable, and where density of wasps and their hosts is low and patchily distributed. Asexuals instead are common in anthropic environments (e.g., grain stores) where host outbreaks offer periods when egg-load is the main constraint on reproductive output.

METHODS

We present a meta-analysis of known adaptations to these habitats. Differences in behavior, physiology and life-history traits between sexual and asexual wasps were standardized in term of effect size (Cohen's d value; Cohen, 1988).

RESULTS

Seeking consilience from the differences between multiple traits, we found that sexuals invest more in longevity at the expense of egg-load, are more mobile, and display higher plasticity in response to thermal variability than asexual counterparts.

DISCUSSION

Thus, each form has consistent multiple adaptations to the ecological circumstances in the contrasting environments.

Response to Comments on "Ducklings imprint on the relational concept of 'same or different'"

Two Comments by Hupé and by Langbein and Puppe address our choice of statistical analysis in assigning preference between sets of stimuli to individual ducklings in our paper. We believe that our analysis remains the most appropriate approach for our data and experimental design.

Ducklings imprint on the relational concept of "same or different"

The ability to identify and retain logical relations between stimuli and apply them to novel stimuli is known as relational concept learning. This has been demonstrated in a few animal species after extensive reinforcement training, and it reveals the brain's ability to deal with abstract properties. Here we describe relational concept learning in newborn ducklings without reinforced training. Newly hatched domesticated mallards that were briefly exposed to a pair of objects that were either the same or different in shape or color later preferred to follow pairs of new objects exhibiting the imprinted relation. Thus, even in a seemingly rigid and very rapid form of learning such as filial imprinting, the brain operates with abstract conceptual reasoning, a faculty often assumed to be reserved to highly intelligent organisms.

Increasing the persistence of a heterogeneous behavior chain: Studies of extinction in a rat model of search behavior of working dogs

Dogs trained to search for contraband perform a chain of behavior in which they first search for a target and then make a separate response that indicates to the trainer that they have found one. The dogs often conduct multiple searches without encountering a target and receiving the reinforcer (i.e., no contraband is present). Understanding extinction (i.e., the decline in work rate when reinforcers are no longer encountered) may assist in training dogs to work in conditions where targets are rare. We therefore trained rats on a search-target behavior chain modeled on the search behavior of working dogs. A discriminative stimulus signaled that a search response (e.g., chain pull) led to a second stimulus that set the occasion for a target response (e.g., lever press) that was reinforced by a food pellet. In Experiment 1 training with longer search durations and intermittent (partial) reinforcement of searching (i.e. some trials had no target present) both led to more persistent search responding in extinction. The loss of search behavior in extinction was primarily dependent on the number of non-reinforced searches rather than time searching without reinforcement. In Experiments 2 and 3, delivery of non-contingent reinforcers during extinction increased search persistence provided they had also been presented during training. Thus, results with rats suggest that the persistence of working dog performance (or chained behavior generally) may be improved by training with partial reinforcement of searching and non-contingent reinforcement during both training and work (extinction).

Pea Plants Show Risk Sensitivity

Sensitivity to variability in resources has been documented in humans, primates, birds, and social insects, but the fit between empirical results and the predictions of risk sensitivity theory (RST), which aims to explain this sensitivity in adaptive terms, is weak [1]. RST predicts that agents should switch between risk proneness and risk aversion depending on state and circumstances, especially according to the richness of the least variable option [2]. Unrealistic assumptions about agents' information processing mechanisms and poor knowledge of the extent to which variability imposes specific selection in nature are strong candidates to explain the gap between theory and data. RST's rationale also applies to plants, where it has not hitherto been tested. Given the differences between animals' and plants' information processing mechanisms, such tests should help unravel the conflicts between theory and data. Measuring root growth allocation by split-root pea plants, we show that they favor variability when mean nutrient levels are low and the opposite when they are high, supporting the most widespread RST prediction. However, the combination of non-linear effects of nitrogen availability at local and systemic levels may explain some of these effects as a consequence of mechanisms not necessarily evolved to cope with variance [3, 4]. This resembles animal examples in which properties of perception and learning cause risk sensitivity even though they are not risk adaptations [5].

Asymmetric visual input and route recapitulation in homing pigeons

Pigeons (Columba livia) display reliable homing behaviour, but their homing routes from familiar release points are individually idiosyncratic and tightly recapitulated, suggesting that learning plays a role in route establishment. In light of the fact that routes are learned, and that both ascending and descending visual pathways share visual inputs from each eye asymmetrically to the brain hemispheres, we investigated how information from each eye contributes to route establishment, and how information input is shared between left and right neural systems. Using on-board global positioning system loggers, we tested 12 pigeons' route fidelity when switching from learning a route with one eye to homing with the other, and back, in an A-B-A design. Two groups of birds, trained first with the left or first with the right eye, formed new idiosyncratic routes after switching eyes, but those that flew first with the left eye formed these routes nearer to their original routes. This confirms that vision plays a major role in homing from familiar sites and exposes a behavioural consequence of neuroanatomical asymmetry whose ontogeny is better understood than its functional significance.

Social transmission of tool use and tool manufacture in Goffin cockatoos (Cacatua goffini)

Tool use can be inherited, or acquired as an individual innovation or by social transmission. Having previously reported individual innovative tool use and manufacture by a Goffin cockatoo, we used the innovator (Figaro, a male) as a demonstrator to investigate social transmission. Twelve Goffins saw either demonstrations by Figaro, or 'ghost' controls where tools and/or food were manipulated using magnets. Subjects observing demonstrations showed greater tool-related performance than ghost controls, with all three males in this group (but not the three females) acquiring tool-using competence. Two of these three males further acquired tool-manufacturing competence. As the actions of successful observers differed from those of the demonstrator, result emulation rather than high-fidelity imitation is the most plausible transmission mechanism.

Irrational choice and the value of information

Irrational decision making in humans and other species challenges the use of optimality in behavioural biology. Here we show that such observations are in fact powerful tools to understand the adaptive significance of behavioural mechanisms. We presented starlings choices between probabilistic alternatives, receiving or not information about forthcoming, delayed outcomes after their choices. Subjects could not use this information to alter the outcomes. Paradoxically, outcome information induced loss-causing preference for the lower probability option. The effect depended on time under uncertainty: information given just after each choice caused strong preference for lower probability, but information just before the outcome did not. A foraging analysis shows that these preferences would maximize gains if post-choice information were usable, as when predators abandon a chase when sure of the prey escaping. Our study illustrates how experimentally induced irrational behaviour supports rather than weakens the evolutionary optimality approach to animal behaviour.

Monocular tool control, eye dominance, and laterality in New Caledonian crows

Tool use, though rare, is taxonomically widespread, but morphological adaptations for tool use are virtually unknown. We focus on the New Caledonian crow (NCC, Corvus moneduloides), which displays some of the most innovative tool-related behavior among nonhumans. One of their major food sources is larvae extracted from burrows with sticks held diagonally in the bill, oriented with individual, but not species-wide, laterality. Among possible behavioral and anatomical adaptations for tool use, NCCs possess unusually wide binocular visual fields (up to 60°), suggesting that extreme binocular vision may facilitate tool use. Here, we establish that during natural extractions, tool tips can only be viewed by the contralateral eye. Thus, maintaining binocular view of tool tips is unlikely to have selected for wide binocular fields; the selective factor is more likely to have been to allow each eye to see far enough across the midsagittal line to view the tool's tip monocularly. Consequently, we tested the hypothesis that tool side preference follows eye preference and found that eye dominance does predict tool laterality across individuals. This contrasts with humans' species-wide motor laterality and uncorrelated motor-visual laterality, possibly because bill-held tools are viewed monocularly and move in concert with eyes, whereas hand-held tools are visible to both eyes and allow independent combinations of eye preference and handedness. This difference may affect other models of coordination between vision and mechanical control, not necessarily involving tools.

Combinatory actions during object play in psittaciformes (Diopsittaca nobilis, Pionites melanocephala, Cacatua goffini) and corvids (Corvus corax, C. monedula, C. moneduloides)

The playful (i.e., not overtly functional) combination of objects is considered a potential ontogenetic and phylogenetic precursor of technical problem solving abilities, as it may lead to affordance learning and honing of mechanical skills. We compared such activities in 6 avian species: 3 psittaciforms (black-headed caiques, red-shouldered macaws, and Goffin cockatoos) and 3 corvids (New Caledonian crows, ravens, and jackdaws). Differences in the type and frequency of object combinations were consistent with species' ecology. Object caching was found predominately in common ravens, which frequently cache food. The most intrinsically structured object combinations were found in New Caledonian crows and Goffin cockatoos, which both stand out for their problem solving abilities in physical tasks. Object insertions prevailed in New Caledonian crows that naturally extract food using tools. Our results support the idea that playful manipulations of inedible objects are linked to physical cognition and problem-solving abilities.

Foraging behaviour in guinea pigs: further tests of the marginal value theorem

We studied the foraging behaviour of guinea pigs (Cavia porcellus) in laboratory environments with a single patch type. Six experiments were designed to test predictions of the marginal value theorem (MVT) for various foraging problems in a constant physical setting. In Part one (experiments I, I', and II) we used patches with resource depression. In experiment I there were two treatments, which differed in the function relating cumulative food gain to time in the patch. Experiment I' was a replicate of experiment I with greater differences in patch quality between treatments. In experiment II the treatments differed in the travel requirement between patches, while the patch gain function remained the same throughout. In experiments III, IV and V (Part two) there were patches with linear gain function and sudden exhaustion, and two treatments in each experiment. The treatments differed in prey encounter rate, maximal number of prey per patch, and travel time, respectively. In the six experiments the MVT predictions for prey per patch visit were qualitatively supported by the experimental results, and in most cases the quantitative fit was also good. Giving up times were longer than predicted. We conclude that the hypothesis of rate maximization, in spite of failing to predict some aspects of the results, provides a suitable framework for examining the foraging behaviour of this species.

Sexual differences in memory in shiny cowbirds

Avian brood parasites depend on other species, the hosts, to raise their offspring. During the breeding season, parasitic cowbirds (Molothrus sp.) search for potential host nests to which they return for laying a few days after first locating them. Parasitic cowbirds have a larger hippocampus/telencephalon volume than non-parasitic species; this volume is larger in the sex involved in nest searching (females) and it is also larger in the breeding than in the non-breeding season. In nature, female shiny cowbirds Molothrus bonariensis search for nests without the male's assistance. Here we test whether, in association with these neuroanatomical and behavioural differences, shiny cowbirds display sexual differences in a memory task in the laboratory. We used a task consisting of finding food whose location was indicated either by the appearance or the location of a covering disk. Females learnt to retrieve food faster than males when food was associated with appearance cues, but we found no sexual differences when food was associated with a specific location. Our results are consistent with the view that parasitism and its neuroanatomical correlates affect performance in memory tasks, but the effects we found were not in the expected direction, emphasising that the nature of avian hippocampal function and its sexual differences are not yet understood.

Object caching in corvids: incidence and significance

Food caching is a paramount model for studying relations between cognition, brain organisation and ecology in corvids. In contrast, behaviour towards inedible objects is poorly examined and understood. We review the literature on object caching in corvids and other birds, and describe an exploratory study on object caching in ravens, New Caledonian crows and jackdaws. The captive adult birds were presented with an identical set of novel objects adjacent to food. All three species cached objects, which shows the behaviour not to be restricted to juveniles, food cachers, tool-users or individuals deprived of cacheable food. The pattern of object interaction and caching did not mirror the incidence of food caching: the intensely food caching ravens indeed showed highest object caching incidence, but the rarely food caching jackdaws cached objects to similar extent as the moderate food caching New Caledonian crows. Ravens and jackdaws preferred objects with greater sphericity, but New Caledonian crows preferred stick-like objects (similar to tools). We suggest that the observed object caching might have been expressions of exploration or play, and deserves being studied in its own right because of its potential significance for tool-related behaviour and learning, rather than as an over-spill from food-caching research. This article is part of a Special Issue entitled: CO3 2013.

Explorative learning and functional inferences on a five-step means-means-end problem in Goffin's cockatoos (Cacatuagoffini)

To investigate cognitive operations underlying sequential problem solving, we confronted ten Goffin's cockatoos with a baited box locked by five different inter-locking devices. Subjects were either naïve or had watched a conspecific demonstration, and either faced all devices at once or incrementally. One naïve subject solved the problem without demonstration and with all locks present within the first five sessions (each consisting of one trial of up to 20 minutes), while five others did so after social demonstrations or incremental experience. Performance was aided by species-specific traits including neophilia, a haptic modality and persistence. Most birds showed a ratchet-like progress, rarely failing to solve a stage once they had done it once. In most transfer tests subjects reacted flexibly and sensitively to alterations of the locks' sequencing and functionality, as expected from the presence of predictive inferences about mechanical interactions between the locks.

Context-dependent preferences in starlings: linking ecology, foraging and choice

Foraging animals typically encounter opportunities that they either pursue or skip, but occasionally meet several alternatives simultaneously. Behavioural ecologists predict preferences using absolute properties of each option, while decision theorists focus on relative evaluations at the time of choice. We use European starlings (Sturnus vulgaris) to integrate ecological reasoning with decision models, linking and testing hypotheses for value acquisition and choice mechanism. We hypothesise that options' values depend jointly on absolute attributes, learning context, and subject's state. In simultaneous choices, preference could result either from comparing subjective values using deliberation time, or from processing each alternative independently, without relative comparisons. The combination of the value acquisition hypothesis and independent processing at choice time has been called the Sequential Choice Model. We test this model with options equated in absolute properties to exclude the possibility of preference being built at the time of choice. Starlings learned to obtain food by responding to four stimuli in two contexts. In context [AB], they encountered options A₅ or B₁₀ in random alternation; in context [CD], they met C₁₀ or D₂₀. Delay to food is denoted, in seconds, by the suffixes. Observed latency to respond (L_i) to each option alone (our measure of value) ranked thus: L_A≈L_C<L_B<<L_D, consistently with value being sensitive to both delay and learning context. We then introduced simultaneous presentations of A₅ vs. C₁₀ and B₁₀ vs. C₁₀, using latencies in no-choice tests to predict sign and strength of preference in pairings. Starlings preferred A₅ over C₁₀ and C₁₀ over B₁₀. There was no detectable evaluation time, and preference magnitude was predictable from latency differentials. This implies that value reflects learning rather than choice context, that preferences are not constructed by relative judgements at the time of choice, and that mechanisms adapted for sequential decisions are effective to predict choice behaviour.

Starlings uphold principles of economic rationality for delay and probability of reward

Rationality principles are the bedrock of normative theories of decision-making in biology and microeconomics, but whereas in microeconomics, consistent choice underlies the notion of utility; in biology, the assumption of consistent selective pressures justifies modelling decision mechanisms as if they were designed to maximize fitness. In either case, violations of consistency contradict expectations and attract theoretical interest. Reported violations of rationality in non-humans include intransitivity (i.e. circular preferences) and lack of independence of irrelevant alternatives (changes in relative preference between options when embedded in different choice sets), but the extent to which these observations truly represent breaches of rationality is debatable. We tested both principles with starlings (Sturnus vulgaris), training subjects either with five options differing in food delay (exp. 1) or with six options differing in reward probability (exp. 2), before letting them choose repeatedly one option out of several binary and trinary sets of options. The starlings conformed to economic rationality on both tests, showing strong stochastic transitivity and no violation of the independence principle. These results endorse the rational choice and optimality approaches used in behavioural ecology, and highlight the need for functional and mechanistic enquiring when apparent violations of such principles are observed.

Risk-sensitivity: crossroads for theories of decision-making

Most actions result in one of a set of possible outcomes. To understand how this uncertainty, or risk, affects animals' decision-making some researchers take a normative approach, asking how an animal should respond to risk if it is maximizing its fitness. Others focus on predicting responses to risk by generalizing from regularities in behavioural data, without reference to cognitive processes. Yet others infer cognitive processes from observed behaviour and ask what actions are predicted when these processes interact with risk. The normative approach (Risk-sensitivity Theory; RST) is unique in predicting a shift in a subject's response to risk as a function of its resource budget, but the predictions of this theory are not yet widely confirmed. In fact, evidence suggests a strong bias towards risk-proneness when delay to reward is risky and risk-aversion when amount of reward is risky, a pattern not readily explained by RST. Extensions of learning theory and of Scalar Expectancy Theory provide process-based explanations for these findings but do not handle preference shifts or provide evolutionary justification for the processes assumed. In this review we defend the view that risk-sensitivity must be studied with theoretical plurality.

Pro-sociality without empathy

Empathy, the capacity to recognize and share feelings experienced by another individual, is an important trait in humans, but is not the same as pro-sociality, the tendency to behave so as to benefit another individual. Given the importance of understanding empathy's evolutionary emergence, it is unsurprising that many studies attempt to find evidence for it in other species. To address the question of what should constitute evidence for empathy, we offer a critical comparison of two recent studies of rescuing behaviour that report similar phenomena but are interpreted very differently by their authors. In one of the studies, rescue behaviour in rats was interpreted as providing evidence for empathy, whereas in the other, rescue behaviour in ants was interpreted without reference to sharing of emotions. Evidence for empathy requires showing that actor individuals possess a representation of the receiver's emotional state and are driven by the psychological goal of improving its wellbeing. Proving psychological goal-directedness by current standards involves goal-devaluation and causal sensitivity protocols, which, in our view, have not been implemented in available publications. Empathy has profound significance not only for cognitive and behavioural sciences but also for philosophy and ethics and, in our view, remains unproven outside humans.

Brood parasite eggs enhance egg survivorship in a multiply parasitized host

Despite the costs to avian parents of rearing brood parasitic offspring, many species do not reject foreign eggs from their nests. We show that where multiple parasitism occurs, rejection itself can be costly, by increasing the risk of host egg loss during subsequent parasite attacks. Chalk-browed mockingbirds (Mimus saturninus) are heavily parasitized by shiny cowbirds (Molothrus bonariensis), which also puncture eggs in host nests. Mockingbirds struggle to prevent cowbirds puncturing and laying, but seldom remove cowbird eggs once laid. We filmed cowbird visits to nests with manipulated clutch compositions and found that mockingbird eggs were more likely to escape puncture the more cowbird eggs accompanied them in the clutch. A Monte Carlo simulation of this 'dilution effect', comparing virtual hosts that systematically either reject or accept parasite eggs, shows that acceptors enjoy higher egg survivorship than rejecters in host populations where multiple parasitism occurs. For mockingbirds or other hosts in which host nestlings fare well in parasitized broods, this benefit might be sufficient to offset the fitness cost of rearing parasite chicks, making egg acceptance evolutionarily stable. Thus, counterintuitively, high intensities of parasitism might decrease or even reverse selection pressure for host defence via egg rejection.

Rational choice, context dependence, and the value of information in European starlings (Sturnus vulgaris)

Both human and nonhuman decision-makers can deviate from optimal choice by making context-dependent choices. Because ignoring context information can be beneficial, this is called a "less-is-more effect." The fact that organisms are so sensitive to the context is thus paradoxical and calls for the inclusion of an ecological perspective. In an experiment with starlings, adding cues that identified the context impaired performance in simultaneous prey choices but improved it in sequential prey encounters, in which subjects could reject opportunities in order to search instead in the background. Because sequential prey encounters are likely to be more frequent in nature, storing and using contextual information appears to be ecologically rational on balance by conditioning acceptance of each opportunity to the relative richness of the background, even if this causes context-dependent suboptimal preferences in (less-frequent) simultaneous choices. In ecologically relevant scenarios, more information seems to be more.

Cognitive mechanisms of risky choice: is there an evaluation cost?

We contrast two classes of choice processes, those assuming time-consuming comparisons and those where stimuli for each option act independently, competing for expression by cross censorship. The Sequential Choice Model (SCM) belongs in the latter category, and has received empirical support in several procedures involving deterministic alternatives. Here we test this model in risky choices. In two treatments, each with five conditions, European starlings (Sturnus vulgaris) faced choices between options with unpredictable outcomes and risk-free alternatives. In the delay treatment the five conditions involved choices between a variable option offering two equiprobable delays to reward and a fixed option with delay differing between conditions. The amount treatment was structurally similar, but amount of reward rather than delay was manipulated. As assumed (and required) by the SCM, latency to respond in no-choice trials reflected each option's richness with respect to the background alternatives, and, crucially, preferences in simultaneous choices were predictable from latencies to each option in forced trials. However, we did not detect reliable differences in response times between forced and choice trials, neither the lengthening expected from evaluation models nor the shortening expected from the SCM.

Flexibility in problem solving and tool use of kea and New Caledonian crows in a multi access box paradigm

Parrots and corvids show outstanding innovative and flexible behaviour. In particular, kea and New Caledonian crows are often singled out as being exceptionally sophisticated in physical cognition, so that comparing them in this respect is particularly interesting. However, comparing cognitive mechanisms among species requires consideration of non-cognitive behavioural propensities and morphological characteristics evolved from different ancestry and adapted to fit different ecological niches. We used a novel experimental approach based on a Multi-Access-Box (MAB). Food could be extracted by four different techniques, two of them involving tools. Initially all four options were available to the subjects. Once they reached criterion for mastering one option, this task was blocked, until the subjects became proficient in another solution. The exploratory behaviour differed considerably. Only one (of six) kea and one (of five) NCC mastered all four options, including a first report of innovative stick tool use in kea. The crows were more efficient in using the stick tool, the kea the ball tool. The kea were haptically more explorative than the NCC, discovered two or three solutions within the first ten trials (against a mean of 0.75 discoveries by the crows) and switched more quickly to new solutions when the previous one was blocked. Differences in exploration technique, neophobia and object manipulation are likely to explain differential performance across the set of tasks. Our study further underlines the need to use a diversity of tasks when comparing cognitive traits between members of different species. Extension of a similar method to other taxa could help developing a comparative cognition research program.

Inclusive fitness theory and eusociality

Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.

On the evolutionary and ontogenetic origins of tool-oriented behaviour in New Caledonian crows (Corvus moneduloides)

New Caledonian crows (Corvus moneduloides) are prolific tool users in captivity and in the wild, and have an inherited predisposition to express tool-oriented behaviours. To further understand the evolution and development of tool use, we compared the development of object manipulation in New Caledonian crows and common ravens (Corvus corax), which do not routinely use tools. We found striking qualitative similarities in the ontogeny of tool-oriented behaviour in New Caledonian crows and food-caching behaviour in ravens. Given that the common ancestor of New Caledonian crows and ravens was almost certainly a caching species, we therefore propose that the basic action patterns for tool use in New Caledonian crows may have their evolutionary origins in caching behaviour. Noncombinatorial object manipulations had similar frequencies in the two species. However, frequencies of object combinations that are precursors to functional behaviour increased in New Caledonian crows and decreased in ravens throughout the study period, ending 6 weeks post-fledging. These quantitative observations are consistent with the hypothesis that New Caledonian crows develop tool-oriented behaviour because of an increased motivation to perform object combinations that facilitate the necessary learning.

The ecological significance of tool use in New Caledonian crows

Tool use is so rare in the animal kingdom that its evolutionary origins cannot be traced with comparative analyses. Valuable insights can be gained from investigating the ecological context and adaptive significance of tool use under contemporary conditions, but obtaining robust observational data is challenging. We assayed individual-level tool-use dependence in wild New Caledonian crows by analyzing stable isotope profiles of the birds' feathers, blood, and putative food sources. Bayesian diet-mixing models revealed that a substantial amount of the crows' protein and lipid intake comes from prey obtained with stick tools--wood-boring beetle larvae. Our calculations provide estimates of larva-intake rates and show that just a few larvae can satisfy a crow's daily energy requirements, highlighting the substantial rewards available to competent tool users.