New Caledonian Crows Research Articles

Design complexity in termite-fishing tools of chimpanzees (Pan troglodytes).

Adopting the approach taken with New Caledonian crows (Corvus moneduloides), we present evidence of design complexity in one of the termite-fishing tools of chimpanzees (Pan troglodytes) in the Goualougo Triangle, Republic of Congo. Prior to termite fishing, chimpanzees applied a set of deliberate, distinguishable actions to modify herb stems to fashion a brush-tipped probe, which is different from the form of fishing tools used by chimpanzees in East and West Africa. This means that 'brush-tipped fishing probes', unlike 'brush sticks', are not a by-product of use but a deliberate design feature absent in other chimpanzee populations. The specialized modifications to prepare the tool for termite fishing, measures taken to repair non-functional brushes and appropriate orientation of the modified end suggest that these wild chimpanzees are attentive to tool modifications. We also conducted experimental trials that showed that a brush-tipped probe is more effective in gathering insects than an unmodified fishing probe. Based on these findings, we suggest that chimpanzees in the Congo Basin have developed an improved fishing probe design.

Grass-Stem Tool use in New Caledonian CrowsCorvus moneduloides

We report an observation of a wild New Caledonian Crow Corvus moneduloides manufacturing two tools from dry grass stems, and using them to extract lizards from the crevices of a fencepost. We recovered one of the tools and were able to examine the raw material from which tools had been manufactured. This confirms our earlier observations with animal-borne video cameras, where we inferred use of this hitherto undocumented tool material from frame-by-frame analysis of video footage.

Extraordinary large brains in tool-using New Caledonian crows (Corvus moneduloides)

A general correlation exists between brain weight and higher cognitive ability in birds and mammals. In birds this relationship is especially evident in corvids. These animals are well-known for their flexible behavior and problem-solving abilities, and have relatively large brains associated with a pallial enlargement. At the behavioral level, New Caledonian crows stand out amongst corvids because of their impressive object manipulation skills both in the wild and in the laboratory. However, nothing is known about the relative size of their brains. Here we show that NC crows have highly encephalised brains relative to most other birds that have been studied. We compared the relative brain size of five NC crows with combined data for four passerine species (7 European carrion crows, 2 European magpies, 3 European jays and 4 domestic sparrows) and found that NC crows had significantly larger brains. A comparison only with the seven carrion crows also revealed significantly larger brains for NC crows. When compared with brain data for 140 avian species from the literature, the NC crow had one of the highest degrees of encephalisation, exceeding that of the 7 other Corvidae in the data set.

Introduced Lantana camara used as tools by New Caledonian crows (Corvus moneduloides)

New Caledonian crows commonly use sticks and similar plant material as hooked and non‐hooked tools to extract prey. They are known to target certain tree species that produce twigs of the right natural shape for easy conversion into tools. All previously identified species supplying tool materials have been native or endemic to New Caledonia. Here I report that crows living in disturbed habitats also use the barbed twigs of an introduced climbing plant, Lantana camara, as tools. Over an 8‐year period I collected 12 L. camara tools used by NC crows at three locations: Bourail and Sarraméa, on mainland Grande Terre, and on the island of Maré. I found these tools left in natural probe sites (Bourail and Sarraméa) or at artificial feeding sites (Maré), but I do not know if the crows targeted L. camara or simply used the closest suitable material. Nevertheless, the use of L. camara indicates that the behaviour of certain free‐living NC crows is sufficiently flexible to enable them to evaluate and use exotic plants for tool material.

Do wild New Caledonian crows (Corvus moneduloides) attend to the functional properties of their tools?

New Caledonian crows are the most proficient non-hominin tool manufacturers but the cognition behind their remarkable skills remains largely unknown. Here we investigate if they attend to the functional properties of the tools that they routinely use in the wild. Pandanus tools have natural barbs along one edge that enable them to function as hooking implements when the barbs face backwards from the working tip. In experiment 1 we presented eight crows with either a non-functional ('upside-down') or a functional pandanus tool in a baited hole. Four of the crows never flipped the tools. The behaviour of the four flipping birds suggested that they had a strategy of flipping a tool when it was not working. Observations of two of the eight crows picking up pandanus tools at feeding tables in the wild supported the lack of attention to barb direction. In experiment 2 we gave six of the eight crows a choice of either a barbed or a barbless pandanus tool. Five of the crows chose tools at random, which further supported the findings in experiment 1 that the crows paid little or no attention to the barbs. In contrast, a third experiment found that seven out of eight crows flipped non-functional stick tools significantly more than functional ones. Our findings indicate that the crows do not consistently attend to the presence or orientation of barbs on pandanus tools. Successful pandanus tool use in the wild seems to rely on behavioural strategies formed through associative learning, including procedural knowledge about the sequence of operations required to make a successful pandanus tool.

Video Cameras on Wild Birds

New Caledonian crows (Corvus moneduloides) are renowned for using tools for extractive foraging, but the ecological context of this unusual behavior is largely unknown. We developed miniaturized, animal-borne video cameras to record the undisturbed behavior and foraging ecology of wild, free-ranging crows. Our video recordings enabled an estimate of the species' natural foraging efficiency and revealed that tool use, and choice of tool materials, are more diverse than previously thought. Video tracking has potential for studying the behavior and ecology of many other bird species that are shy or live in inaccessible habitats.

Cognitive requirements for tool use by New Caledonian crows (Corvus moneduloides)

Cumulative technological evolution has been suggested to explain the existence of different pandanus tool designs manufactured by New Caledonian crows. Circumstantial evidence from the distribution of the three tool designs that they manufacture suggests transmission of the designs probably involves accurate social learning, a characteristic considered essential for the cumulative evolution of tools. Recently, Kenward et al. (2005) reported that four hand‐raised crows developed basic stick tool use without social learning. This finding cast doubt on the importance of social learning in the evolution of crows’ pandanus tools in the wild. Here, we report that a naïve male crow at Parc Zoo‐Forestier, Nouméa, developed proficient stick tool use without social input in 2002. In 2004, four captive crows, including the naïve male, that were inexperienced with pandanus material were given an opportunity to use and/or manufacture pandanus tools. Only two of the four birds used the tools but none manufactured tools. Our preliminary findings and the work with the four hand‐raised crows keep open the possibility that the evolution of crows’ pandanus tool designs is based on social learning. We propose that social learning and a disposition to develop basic tool use without social input are both essential cognitive requirements for cumulative technological evolution.

Development of tool use in New Caledonian crows: inherited action patterns and social influences

New Caledonian crows, Corvus moneduloides, are the most advanced avian tool makers and tool users. We previously reported that captive-bred isolated New Caledonian crows spontaneously use twig tools and cut tools out of Pandanus spp. tree leaves, an activity possibly under cultural influence in the wild. However, what aspects of these behaviours are inherited and how they interact with individual and social experience remained unknown. To examine the interaction between inherited traits, individual learning and social transmission, we observed the ontogeny of twig tool use in hand-reared juveniles. Successful food retrieval was preceded by stereotyped object manipulation action patterns that resembled components of the mature behaviour, demonstrating that tool-oriented behaviours in this species are an evolved specialization. However, there was also an effect of social learning: juveniles that had received demonstrations of twig tool use by their human foster parent showed higher levels of handling and insertion of twigs than did their naive counterparts; a choice experiment showed that they preferred to handle objects that they had seen being manipulated by their human foster parent. Our observations are consistent with the hypothesis that individual learning, cultural transmission and creative problem solving all contribute to the acquisition of the tool-oriented behaviours in the wild, but inherited species-typical action patterns have a greater role than has been recognized.

A New Caledonian crow (Corvus moneduloides) creatively re-designs tools by bending or unbending aluminium strips

Previous observations of a New Caledonian crow (Corvus moneduloides) spontaneously bending wire and using it as a hook [Weir et al. (2002) Science 297:981] have prompted questions about the extent to which these animals 'understand' the physical causality involved in how hooks work and how to make them. To approach this issue we examine how the same subject ("Betty") performed in three experiments with novel material, which needed to be either bent or unbent in order to function to retrieve food. These tasks exclude the possibility of success by repetition of patterns of movement similar to those employed before. Betty quickly developed novel techniques to bend the material, and appropriately modified it on four of five trials when unbending was required. She did not mechanically apply a previously learned set of movements to the new situations, and instead sought new solutions to each problem. However, the details of her behaviour preclude concluding definitely that she understood and planned her actions: in some cases she probed with the unmodified tools before modifying them, or attempted to use the unmodified (unsuitable) end of the tool after modification. Gauging New Caledonian crows' level of understanding is not yet possible, but the observed behaviour is consistent with a partial understanding of physical tasks at a level that exceeds that previously attained by any other non-human subject, including apes.

The right tool for the job: what strategies do wild New Caledonian crows use?

New Caledonian crows Corvus moneduloides (NC crows) display sophisticated tool manufacture in the wild, but the cognitive strategy underlying these skills is poorly understood. Here, we investigate what strategy two free-living NC crows used in response to a tool-length task. The crows manufactured tools to extract food from vertical holes of different depths. The first tools they made in visits were of a similar length regardless of the hole depth. The typical length was usually too short to extract food from the deep holes, which ruled out a strategy of immediate causal inference on the first attempt in a trial. When the first tool failed, the crows made second tools significantly longer than the unsuccessful first tools. There was no evidence that the crows made the lengths of first tools to directly match hole depth. We argue that NC crows may generally use a two-stage heuristic strategy to solve tool problems and that performance on the first attempt in a trial is not necessarily the 'gold standard' for assessing folk physics.

Behavioural ecology: Tool manufacture by naive juvenile crows

New Caledonian crows (Corvus moneduloides) are the most prolific avian tool-users. Regional variation in the shape of their tools may be the result of cumulative cultural evolution--a phenomenon considered to be a hallmark of human culture. Here we show that hand-raised juvenile New Caledonian crows spontaneously manufacture and use tools, without any contact with adults of their species or any prior demonstration by humans. Our finding is a crucial step towards producing informed models of cultural transmission in this species, and in animals in general.

Lateralization of tool use in New Caledonian crows ( Corvus moneduloides )

We studied laterality of tool use in 10 captive New Caledonian (NC) crows (Corvus moneduloides). All subjects showed near-exclusive individual laterality, but there was no overall bias in either direction (five were left-lateralized and five were right-lateralized). This is consistent with results in non-human primates, which show strong individual lateralization for tool use (but not for other activities), and also with observations of four wild NC crows by Rutledge & Hunt. Jointly, these results contrast with observations that the crows have a population-level bias for manufacturing tools from the left edges of Pandanus sp. leaves, and suggest that the manufacture and use of tools in this species may have different neural underpinnings.

Morphology and sexual dimorphism of the New Caledonian Crow Corvus moneduloides, with notes on its behaviour and ecology

New Caledonian Crows Corvus moneduloides are known to be extraordinary tool makers and users, but little is known of other aspects of their biology. Here, we report recent field observations of their behaviour and ecology, along with measurements of 19 morphological traits and two flight performance parameters taken from 22 captured Crows. These measurements showed that the Crows were sexually dimorphic in size (the males were larger) but not in shape. We also found that the crows lived in mixed‐sex groups, and we observed juvenile‐type begging behaviour and feeding by regurgitation, which supports the hypothesis that these may be family groups.

Lateralized tool use in wild New Caledonian crows

Many vertebrate species exhibit sensory and motor asymmetries. Laterality studies of tool use have focused on primates, where hemispheric asymmetries, manifested behaviourally in hand preferences, are thought to be associated with complex motor tasks. Here we report strong individual lateralization for tool use in birds. New Caledonian crows, Corvus moneduloides, hold stick tools with their bills while foraging, often with the nonworking end laterally positioned on one side of the head and the working end possibly positioned in the binocular field. We observed four wild crows to determine whether tools were consistently held on one side. All crows showed a significant preference (two right, two left). This preference was independent of any asymmetry in tool manufacture and held for artificial holes similarly accessible for tools held on either side. This is the first demonstration of lateralized tool use in a nonprimate. In addition, all 173 tools used unilaterally were held only on a crow's preferred side. Such pronounced individual laterality for tool use in natural conditions has previously been reported only in humans and chimpanzees.

Direct observations of pandanus-tool manufacture and use by a New Caledonian crow (Corvus moneduloides).

New Caledonian crows are reported to have impressive pandanus-tool manufacture abilities. These claims are based on an extensive artefact record. However, inferring behavioural and cognitive abilities without direct observation of tool manufacture is problematic. Here we report (and document on video) direct observations of a crow making and using stepped pandanus tools at Pic Ningua. We observed (1) a bias for making tools on left edges consistent with that previously found at the site, (2) faithful manufacture of a stepped design with high overall congruence in the shapes of tools, (3) the use of convergent rips to first form the tapered end working away from the trunk then the wide end working towards the trunk, (4) appropriate functional use of stepped tools by use of the leaf-edge barbs to hook food from holes, and (5) consistent holding of tools on the left side of its head when using them. Our observations verify most of the claims based on the artefact record, but the crow's exact manufacture technique was slightly different to that inferred previously.

New Caledonian Crows drop candle-nuts onto rock from communally used forks on branches

Many birds and non-human primates purposely drop or throw down objects from a height to achieve a goal. Tool-using New Caledonian Crows, Corvus moneduloides, are one of the few birds that drop nuts, and do so when standing on a substrate. In this initial study of their nut-dropping, we watched free-living Crows at Sarraméa drop Aleurites moluccana ‘candle-nuts’ from branches onto rock at two locations 200 m apart. Over three consecutive days, Crows dropped nuts 208 and 85 times, respectively, from two branches at one of the locations, and 74 times over three days from one branch at the other location. Most nuts that broke or were damaged and prised open were dropped 2–3 times. Aside from 18 unseen cases, birds released all 349 nuts from forks in the branches, not directly from their bills. Our findings confirm early reports that suggested that Crows select branches non-randomly for nut-dropping, drop candle-nuts onto anvils from predetermined locations on branches and communally use nut-dropping branches. In addition, we report here new behaviour associated with animals dropping objects from a height: (i) the placing of objects on a substrate to release them, and (ii) the repeated dropping of objects from the same release position in three-dimensional space by the use of forks in branches. Nut-dropping from forks is well suited for experimental work to investigate the evolution, maintenance and transmission of a novel, object-related foraging behaviour.

Shaping of hooks in New Caledonian crows.

Many animals use tools, but their understanding of physical forces or causal relations is unclear ([1][1], [2][2]). Primates are considered the most versatile and complex tool users, but observations of New Caledonian crows ( Corvus moneduloides ) ([3–5][3]) raise the possibility that these birds

Tool Use by the New Caledonian Crow Corvus moneduloides to Obtain Cerambycidae from Dead Wood

SummaryFrom a successful effort in late 1997 to film crow tool-use with the BBC Natural History Unit, I present the first detailed description of New Caledonian Crows Corvus moneduloides using tools to extract larvae of an endemic Cerambycidae:Prioninae from dead wood. I observed birds over a six-week period at Sarraméa where fallen Aleurites moluccana logs were ‘salted’ with the larvae. Crows habitually used mostly A. moluccana leaf-stems to extract larvae from holes and manufacture was also common when birds removed leaves from leaf-stems before using tools. The techniques of adult crows varied but were more proficient than those of a juvenile crow that frequented the site. Tool-use to extract Cerambycidae from dead wood was probably an important part of the foraging behaviour of the crows year-round. My observations here and elsewhere show that crows in different localities can have distinctly different traditions in their tool behaviour.

Taxonomy of Philopterus (Phthiraptera: Philopteridae) from the Corvidae (Passeriformes), with Descriptions of Nine New Species

Seventeen previously described species of Philopterus are recognized and redescribed. Nine new species are described: clayae (type host Corvus capensis), ptilostomi (type host Ptilostomus afer), dumani (type host Pyrrhocorax graculus), cubensis (type host Corvus nasicus), urocissae (type host Urocissa caerulea), etnersoni (type host Dendrocitta formosae), dalgleishi (type host Corvus tasinanicus), craigi (type host Corvus coronoides), and palmai (type host Corvus moneduloides). Philopterus cristata Malcomson and P. vagabunda Ansari are placed as new junior synonyms of P. crassipes (Burmeister). A key is provided for the identification of these 26 species.