Caledonian Crows Research Articles

Tool bending in New Caledonian crows.

‘Betty’ the New Caledonian crow astonished the world when she ‘spontaneously’ bent straight pieces of garden wire into hooked foraging tools. Recent field experiments have revealed that tool bending is part of the species' natural behavioural repertoire, providing important context for interpreting Betty's iconic wire-bending feat. More generally, this discovery provides a compelling illustration of how natural history observations can inform laboratory-based research into the cognitive capacities of non-human animals.

A novel tool-use mode in animals: New Caledonian crows insert tools to transport objects.

New Caledonian crows (Corvus moneduloides) rely heavily on a range of tools to extract prey. They manufacture novel tools, save tools for later use, and have morphological features that facilitate tool use. We report six observations, in two individuals, of a novel tool-use mode not previously reported in non-human animals. Insert-and-transport tool use involves inserting a stick into an object and then moving away, thereby transporting both object and tool. All transported objects were non-food objects. One subject used a stick to transport an object that was too large to be handled by beak, which suggests the tool facilitated object control. The function in the other cases is unclear but seems to be an expression of play or exploration. Further studies should investigate whether it is adaptive in the wild and to what extent crows can flexibly apply the behaviour in experimental settings when purposive transportation of objects is advantageous.Electronic supplementary materialThe online version of this article (doi:10.1007/s10071-016-1016-z) contains supplementary material, which is available to authorized users.

Ravens, New Caledonian crows and jackdaws parallel great apes in motor self-regulation despite smaller brains.

Overriding motor impulses instigated by salient perceptual stimuli represent a fundamental inhibitory skill. Such motor self-regulation facilitates more rational behaviour, as it brings economy into the bodily interaction with the physical and social world. It also underlies certain complex cognitive processes including decision making. Recently, MacLean et al. (MacLean et al. 2014 Proc. Natl Acad. Sci. USA 111, 2140–2148. (doi:10.1073/pnas.1323533111)) conducted a large-scale study involving 36 species, comparing motor self-regulation across taxa. They concluded that absolute brain size predicts level of performance. The great apes were most successful. Only a few of the species tested were birds. Given birds' small brain size—in absolute terms—yet flexible behaviour, their motor self-regulation calls for closer study. Corvids exhibit some of the largest relative avian brain sizes—although small in absolute measure—as well as the most flexible cognition in the animal kingdom. We therefore tested ravens, New Caledonian crows and jackdaws in the so-called cylinder task. We found performance indistinguishable from that of great apes despite the much smaller brains. We found both absolute and relative brain volume to be a reliable predictor of performance within Aves. The complex cognition of corvids is often likened to that of great apes; our results show further that they share similar fundamental cognitive mechanisms.

Adaptive bill morphology for enhanced tool manipulation in New Caledonian crows.

Early increased sophistication of human tools is thought to be underpinned by adaptive morphology for efficient tool manipulation. Such adaptive specialisation is unknown in nonhuman primates but may have evolved in the New Caledonian crow, which has sophisticated tool manufacture. The straightness of its bill, for example, may be adaptive for enhanced visually-directed use of tools. Here, we examine in detail the shape and internal structure of the New Caledonian crow’s bill using Principal Components Analysis and Computed Tomography within a comparative framework. We found that the bill has a combination of interrelated shape and structural features unique within Corvus, and possibly birds generally. The upper mandible is relatively deep and short with a straight cutting edge, and the lower mandible is strengthened and upturned. These novel combined attributes would be functional for (i) counteracting the unique loading patterns acting on the bill when manipulating tools, (ii) a strong precision grip to hold tools securely, and (iii) enhanced visually-guided tool use. Our findings indicate that the New Caledonian crow’s innovative bill has been adapted for tool manipulation to at least some degree. Early increased sophistication of tools may require the co-evolution of morphology that provides improved manipulatory skills.

Social and Spatial Reintegration Success of New Caledonian Crows (Corvus moneduloides) Released after Aviary Confinement

ABSTRACT Wild birds are sometimes brought into captivity in order to conduct more controlled experiments, then released. Follow up work investigating how successful these birds are at reintegrating into their original habitats are rare. Here, I investigate the reintegration success of 13 New Caledonian Crows (Corvus moneduloides) who spent from 4–210 days in a large outdoor aviary in 2012 and 2014, then were released at their capture site. Five of the crows were monitored by telemetry for 2 weeks after their release in November 2014. In March and April 2015, 12 of the 13 crows were recorded at feeding sites where they were captured. The released crows showed a high degree of site fidelity and appeared to rapidly reintegrate with resident crows in the area. There were two cases of released crows successfully breeding. Long-term stay in captivity appears to have minimal impact on the ability of sub-adult and adult crows to re-establish their wild lifestyles, but juvenile crows <1 year old may find it more d...

Does absolute brain size really predict self-control? Hand-tracking training improves performance on the A-not-B task.

Large-scale, comparative cognition studies are set to revolutionize the way we investigate and understand the evolution of intelligence. However, the conclusions reached by such work have a key limitation: the cognitive tests themselves. If factors other than cognition can systematically affect the performance of a subset of animals on these tests, we risk drawing the wrong conclusions about how intelligence evolves. Here, we examined whether this is the case for the A-not-B task, recently used by MacLean and co-workers to study self-control among 36 different species. Non-primates performed poorly on this task; possibly because they have difficulty tracking the movements of a human demonstrator, and not because they lack self-control. To test this, we assessed the performance of New Caledonian crows on the A-not-B task before and after two types of training. New Caledonian crows trained to track rewards moved by a human demonstrator were more likely to pass the A-not-B test than birds trained on an unrelated choice task involving inhibitory control. Our findings demonstrate that overlooked task demands can affect performance on a cognitive task, and so bring into question MacLean's conclusion that absolute brain size best predicts self-control.

Strong between-site variation in New Caledonian crows' use of hook-tool-making materials.

Functional tool use requires the selection of appropriate raw materials. New Caledonian crows Corvus moneduloides are known for their extraordinary tool‐making behaviour, including the crafting of hooked stick tools from branched vegetation. We describe a surprisingly strong between‐site difference in the plant materials used by wild crows to manufacture these tools: crows at one study site use branches of the non‐native shrub Desmanthus virgatus, whereas only approximately 7 km away, birds apparently ignore this material in favour of the terminal twigs of an as‐yet‐unidentified tree species. Although it is likely that differences in local plant communities drive this striking pattern, it remains to be determined how and why crows develop such strong site‐specific preferences for certain raw materials.

Modeling of Mechanism of Plan Formation by New Caledonian Crows

The current paper analyzes the mechanism of planning by New Caledonian crows. The mechanism uses predictions of results of actions. Namely, our model suggests that for a given situation and a particular action, the crow predicts the next situation. The mechanism of planning includes: 1) generation of needed predictions, 2) formation of a simple knowledge database that describes situations, actions, and results of actions, 3) formation of the plan of actions that result in a goal situation. The knowledge database is a table; each row of the table represents some initial situation, an action, the predicted next situation, and the estimation of a distance between the considered situations and the goal situation. The mental process of plan formation uses this knowledge database. The plan is the chain of consecutive actions. Beginning from the starting situation and executing this chain of actions, the crow obtains the goal situation.

Intelligence Over Time: Intelligence in Corvids and Apes

INTELLEGENCE OVER TIME: THE EVOLUTION OF INTELLIGENCE IN CORVIDS AND APES BY KATIE SANKO K itty, a New Caledonian crow, became famous when National Geographic highlighted her ability to solve a puz- zle that bewildered many five-year-old children. 5 In order to obtain a small piece of meat floating in a tube of water, Kitty placed rocks in a seemingly unrelated tube, causing the water to rise and the meat to float to the top. 5 Kitty and her fellow crows possess remarkable cognitive ability, prompting many to wonder what could be behind the evolution of such intelligence. Animal intelligence is tricky to define, despite the efforts of numerous researchers over the years. A quantitative measure of animal intelligence has yet to be agreed upon. It is often assumed that as brain size (both absolute and relative) increases, so does intelligence. However, both of these measures have been ruled out by bascre- search. For example, cetaceans (whales and dolphins) have a larger absolute brain size than humans, 10 yet humans are considered far more intelligent. Similarly, the shrew’s brain contains 10% of its body mass while a human’s contains only 2%. Generally, the definition of intelligence involves the performance of complex behaviors and the use of novel solutions to problems. 10 Humans are not alone in the possession of great intelligence. In fact, advanced cogni- tion has evolved in many taxa. 9 While the intelligence of primates such as chimpan- zees has been widely publicized, it has also been found that birds in the group of corvids (crows, jays, ravens, ect.) have cog- nitive abilities comparable to apes. 4 Exam- ples of higher cognition in both primates and corvids include object permanence (memory for objects that cannot be seen by the organism), 4 the delay of gratification (control of impulsivity), 4 and mental time travel (memory for past events and plan- ning for future events) 4 and tool making. 1,13 Although the brains of these organisms are structuredof these organisms are struc- tured differently, 4 their intellectual abilities are remarkably similar, 4 thus making the evolution of intelligence in these groups particularly fascinating. The evolution of intelligence in crows and apes can be described as convergent evolu- tion. Convergent evolution is the devel- opment of similar traits in organisms that are not closely related. Although mammals and birds share a common ancestor with all vertebrates, approximately 300 million years separate them from their closest relative, indicating that their advanced cognition must have evolved separately. 4 Currently, there are several hypotheses for the factors behind this convergent evolu- tion. These factors mainly fall under the broad categories of dietary and social. Apes rely on a diet of tropical fruit, and one hypothesis behind their advanced cognition is centered on this diet. Many plants only bear ripe fruit at certain times of the year, and these plants were widely dispersed throughout the habitats of early primates11. Because these primates were often required to travel large distances to forage for food, larger brains and more complex cognition allowed for the pri- mates to travel the most energy-efficient routesw. Corvids, however, do not rely on ripe fruit. Instead, many corvids “cache” food, and cognitive evolution would have aided their common ancestor in remem- bering the location of its caches3. Further- more, corvids such as the Western scrub jay know when the food in their cache is going to spoil and become inedible3. Simi- larly, many corvids steal from the caches of other birds and employ complex strategies to prevent their ownyear, and these plants were widely dispersed throughout the habitats of early primates. 11 Because these primates were often required to travel large FALL 2016 | Berkeley Scientific Journal

Activity profiles and hook-tool use of New Caledonian crows recorded by bird-borne video cameras.

New Caledonian crows are renowned for their unusually sophisticated tool behaviour. Despite decades of fieldwork, however, very little is known about how they make and use their foraging tools in the wild, which is largely owing to the difficulties in observing these shy forest birds. To obtain first estimates of activity budgets, as well as close-up observations of tool-assisted foraging, we equipped 19 wild crows with self-developed miniature video cameras, yielding more than 10 h of analysable video footage for 10 subjects. While only four crows used tools during recording sessions, they did so extensively: across all 10 birds, we conservatively estimate that tool-related behaviour occurred in 3% of total observation time, and accounted for 19% of all foraging behaviour. Our video-loggers provided first footage of crows manufacturing, and using, one of their most complex tool types—hooked stick tools—under completely natural foraging conditions. We recorded manufacture from live branches of paperbark (Melaleuca sp.) and another tree species (thought to be Acacia spirorbis), and deployment of tools in a range of contexts, including on the forest floor. Taken together, our video recordings reveal an ‘expanded’ foraging niche for hooked stick tools, and highlight more generally how crows routinely switch between tool- and bill-assisted foraging.

Hook tool manufacture in New Caledonian crows: behavioural variation and the influence of raw materials.

BackgroundNew Caledonian crows use a range of foraging tools, and are the only non-human species known to craft hooks. Based on a small number of observations, their manufacture of hooked stick tools has previously been described as a complex, multi-stage process. Tool behaviour is shaped by genetic predispositions, individual and social learning, and/or ecological influences, but disentangling the relative contributions of these factors remains a major research challenge. The properties of raw materials are an obvious, but largely overlooked, source of variation in tool-manufacture behaviour. We conducted experiments with wild-caught New Caledonian crows, to assess variation in their hooked stick tool making, and to investigate how raw-material properties affect the manufacture process.ResultsIn Experiment 1, we showed that New Caledonian crows’ manufacture of hooked stick tools can be much more variable than previously thought (85 tools by 18 subjects), and can involve two newly-discovered behaviours: ‘pulling’ for detaching stems and bending of the tool shaft. Crows’ tool manufactures varied significantly: in the number of different action types employed; in the time spent processing the hook and bending the tool shaft; and in the structure of processing sequences. In Experiment 2, we examined the interaction of crows with raw materials of different properties, using a novel paradigm that enabled us to determine subjects’ rank-ordered preferences (42 tools by 7 subjects). Plant properties influenced: the order in which crows selected stems; whether a hooked tool was manufactured; the time required to release a basic tool; and, possibly, the release technique, the number of behavioural actions, and aspects of processing behaviour. Results from Experiment 2 suggested that at least part of the natural behavioural variation observed in Experiment 1 is due to the effect of raw-material properties.ConclusionsOur discovery of novel manufacture behaviours indicates a plausible scenario for the evolutionary origins, and gradual refinement, of New Caledonian crows’ hooked stick tool making. Furthermore, our experimental demonstration of a link between raw-material properties and aspects of tool manufacture provides an alternative hypothesis for explaining regional differences in tool behaviours observed in New Caledonian crows, and some primate species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-015-0204-7) contains supplementary material, which is available to authorized users.

Experimental resource pulses influence social-network dynamics and the potential for information flow in tool-using crows.

Social-network dynamics have profound consequences for biological processes such as information flow, but are notoriously difficult to measure in the wild. We used novel transceiver technology to chart association patterns across 19 days in a wild population of the New Caledonian crow—a tool-using species that may socially learn, and culturally accumulate, tool-related information. To examine the causes and consequences of changing network topology, we manipulated the environmental availability of the crows' preferred tool-extracted prey, and simulated, in silico, the diffusion of information across field-recorded time-ordered networks. Here we show that network structure responds quickly to environmental change and that novel information can potentially spread rapidly within multi-family communities, especially when tool-use opportunities are plentiful. At the same time, we report surprisingly limited social contact between neighbouring crow communities. Such scale dependence in information-flow dynamics is likely to influence the evolution and maintenance of material cultures.

Processing and visualising association data from animal-borne proximity loggers

With increasing interest in animal social networks, field biologists have started exploring the use of advanced tracking technologies for mapping social encounters in free-ranging subjects. Proximity logging, which involves the use of animal-borne tags with the capacity for two-way communication, has attracted particular attention in recent years. While the basic rationale of proximity logging is straightforward, systems generate very large datasets which pose considerable challenges in terms of processing and visualisation. Technical aspects of data handling are crucial for the success of proximity-logging studies, yet are only rarely reported in full detail. Here, we describe the procedures we employed for mining the data generated by a recent deployment of a novel proximity-logging system, “Encounternet”, to study social-network dynamics in tool-using New Caledonian crows. Our field deployment of an Encounternet system produced some 240,000 encounter logs for 33 crows over a 19-day study period. Using this dataset, we illustrate a range of procedures, including: examination of tag reciprocity (i.e. whether both tags participating in an encounter detected the encounter and, if so, whether their records differed); filtering of data according to a predetermined signal-strength criterion (to enable analyses that focus on encounters within a particular distance range); amalgamation of temporally clustered encounter logs (to remove data artefacts and to enable robust analysis of biological patterns); and visualisation of dynamic network data as timeline plots (which can be used, among other things, to visualise the simulated diffusion of information). Researchers wishing to study animal social networks with proximity-logging systems should be aware of the complexities involved. Successful data analysis requires not only a sound understanding of hardware and software operation, but also bioinformatics expertise. Our paper aims to facilitate future projects by explaining in detail some of the subtleties that are easily overlooked in first-pass analyses, but are key for reaching valid biological conclusions. We hope that this work will prove useful to other researchers, especially when read in conjunction with three recently published companion papers that report aspects of system calibration and key results.

No conclusive evidence that corvids can create novel causal interventions.

Jacobs et al. [[1][1]] raise some interesting and important questions about our recent paper in which New Caledonian crows were unable to design a novel causal intervention [[2][2]]. These concern the problematic nature of animal/human comparisons, the complexity of our apparatus, other evidence

How New Caledonian crows solve novel foraging problems and what it means for cumulative culture.

New Caledonian crows make and use tools, and tool types vary over geographic landscapes. Social learning may explain the variation in tool design, but it is unknown to what degree social learning accounts for the maintenance of these designs. Indeed, little is known about the mechanisms these crows use to obtain information from others, despite the question's importance in understanding whether tool behavior is transmitted via social, genetic, or environmental means. For social transmission to account for tool-type variation, copying must utilize a mechanism that is action specific (e.g., pushing left vs. right) as well as context specific (e.g., pushing a particular object vs. any object). To determine whether crows can copy a demonstrator's actions as well as the contexts in which they occur, we conducted a diffusion experiment using a novel foraging task. We used a nontool task to eliminate any confounds introduced by individual differences in their prior tool experience. Two groups had demonstrators (trained in isolation on different options of a four-option task, including a two-action option) and one group did not. We found that crows socially learn about context: After observers see a demonstrator interact with the task, they are more likely to interact with the same parts of the task. In contrast, observers did not copy the demonstrator's specific actions. Our results suggest it is unlikely that observing tool-making behavior transmits tool types. We suggest it is possible that tool types are transmitted when crows copy the physical form of the tools they encounter.

New Caledonian crows rapidly solve a collaborative problem without cooperative cognition.

There is growing comparative evidence that the cognitive bases of cooperation are not unique to humans. However, the selective pressures that lead to the evolution of these mechanisms remain unclear. Here we show that while tool-making New Caledonian crows can produce collaborative behavior, they do not understand the causality of cooperation nor show sensitivity to inequity. Instead, the collaborative behavior produced appears to have been underpinned by the transfer of prior experience. These results suggest that a number of possible selective pressures, including tool manufacture and mobbing behaviours, have not led to the evolution of cooperative cognition in this species. They show that causal cognition can evolve in a domain specific manner–understanding the properties and flexible uses of physical tools does not necessarily enable animals to grasp that a conspecific can be used as a social tool.

Context-dependent 'safekeeping' of foraging tools in New Caledonian crows.

Several animal species use tools for foraging, such as sticks to extract embedded arthropods and honey, or stones to crack open nuts and eggs. While providing access to nutritious foods, these behaviours may incur significant costs, such as the time and energy spent searching for, manufacturing and transporting tools. These costs can be reduced by re-using tools, keeping them safe when not needed. We experimentally investigated what New Caledonian crows do with their tools between successive prey extractions, and whether they express tool ‘safekeeping’ behaviours more often when the costs (foraging at height), or likelihood (handling of demanding prey), of tool loss are high. Birds generally took care of their tools (84% of 176 prey extractions, nine subjects), either trapping them underfoot (74%) or storing them in holes (26%)—behaviours we also observed in the wild (19 cases, four subjects). Moreover, tool-handling behaviour was context-dependent, with subjects: keeping their tools safe significantly more often when foraging at height; and storing tools significantly more often in holes when extracting more demanding prey (under these conditions, foot-trapping proved challenging). In arboreal environments, safekeeping can prevent costly tool losses, removing a potentially important constraint on the evolution of habitual and complex tool behaviour.

Corvids create novel causal interventions after all.

Using a novel paradigm, Taylor et al. [[1][1]] recently investigated whether New Caledonian crows make causal interventions in comparison to 24-month-old children. They view a causal intervention as the ability, after having only observed a correlation between cause and effect, to produce a novel

Calibrating animal-borne proximity loggers.

Summary Growing interest in the structure and dynamics of animal social networks has stimulated efforts to develop automated tracking technologies that can reliably record encounters in free‐ranging subjects. A particularly promising approach is the use of animal‐attached ‘proximity loggers’, which collect data on the incidence, duration and proximity of spatial associations through inter‐logger radio communication. While proximity logging is based on a straightforward physical principle – the attenuation of propagating radio waves with distance – calibrating systems for field deployment is challenging, since most study species roam across complex, heterogeneous environments.In this study, we calibrated a recently developed digital proximity‐logging system (‘Encounternet’) for deployment on a wild population of New Caledonian crows Corvus moneduloides. Our principal objective was to establish a quantitative model that enables robust post hoc estimation of logger‐to‐logger (and, hence, crow‐to‐crow) distances from logger‐recorded signal‐strength values. To achieve an accurate description of the radio communication between crow‐borne loggers, we conducted a calibration exercise that combines theoretical analyses, field experiments, statistical modelling, behavioural observations, and computer simulations.We show that, using signal‐strength information only, it is possible to assign crow encounters reliably to predefined distance classes, enabling powerful analyses of social dynamics. For example, raw data sets from field‐deployed loggers can be filtered at the analysis stage to include predominantly encounters where crows would have come to within a few metres of each other, and could therefore have socially learned new behaviours through direct observation. One of the main challenges for improving data classification further is the fact that crows – like most other study species – associate across a wide variety of habitats and behavioural contexts, with different signal‐attenuation properties.Our study demonstrates that well‐calibrated proximity‐logging systems can be used to chart social associations of free‐ranging animals over a range of biologically meaningful distances. At the same time, however, it highlights that considerable efforts are required to conduct study‐specific system calibrations that adequately account for the biological and technological complexities of field deployments. Although we report results from a particular case study, the basic rationale of our multi‐step calibration exercise applies to many other tracking systems and study species.

Model of Plan Formation by New Caledonian Crows

Abstract The computer model of planning the rather complex behavior by New Caledonian crows is developed and investigated. The model characterizes the following processes: 1) analysis of predictions of elementary actions, 2) generation of a simple knowledge database that describes the set of initial situations, actions, and results of actions, 3) planning a concrete chain of consecutive actions. The model is inspired by the biological experiment on New Caledonian crows.