Oscillatory extraction behaviour suggests functional attributes of crows' hooked-stick tools.

New Caledonian crows are the only nonhuman animals known to craft hooked-sticks for use in foraging. Since their first description over 25 years ago, researchers have been unable to provide a detailed account of how these complex tools function in natural probe sites. Using close-up video footage, we document how a New Caledonian crow operated a hooked-stick to extract a large tree weta from a chamber in a tree trunk.

A genome-wide investigation of adaptive signatures in protein-coding genes related to tool behaviour in New Caledonian and Hawaiian crows.

Very few animals habitually manufacture and use tools. It has been suggested that advanced tool behaviour co-evolves with a suite of behavioural, morphological and life history traits. In fact, there are indications for such an adaptive complex in tool-using crows (genus Corvus species).

New Caledonian crows' basic tool procurement is guided by heuristics, not matching or tracking probe site characteristics.

Contrasting findings made it unclear what cognitive processes New Caledonian crows use to procure suitable tools to solve tool tasks. Most previous studies suggested that their tool procurement is achieved by either trial and error or a simple heuristic. The latter provides a fast and cognitively efficient method for stable, routinized behaviour based on past experience with little or no deliberate decision-making.

New Caledonian crows afford invaluable comparative insights into human cumulative technological culture.

The New Caledonian crow may be the only non-primate species exhibiting cumulative technological culture. Its foraging tools show clear signs of diversification and progressive refinement, and it seems likely that at least some tool-related information is passed across generations via social learning. Here, we explain how these remarkable birds can help us uncover the basic biological processes driving technological progress.

Corvid Technologies: How Do New Caledonian Crows Get Their Tool Designs?

Recent research shows that New Caledonian crows can incorporate information from researcher-made objects into objects they subsequently manufacture. This 'mental template matching' is one of several possible - mutually compatible - mechanisms for the cultural transmission of tool designs among wild crows.

Habitual tool use innovated by free-living New Zealand kea.

The emergence of flexible tool use is rare in the animal kingdom and thought to be largely constrained by either cognitive ability or ecological factors. That mostly birds with a high level of intelligence innovate tool use in captivity is consistent with the former hypothesis. We report here the first documented case of habitual tool use innovated in the wild by a bird species only known to have used tools in captivity.

A new tool-using bird to crow about.

The Hawaiian crow has been revealed as a skilled tool user, confirmed by testing the last members of this endangered species that survive in captivity. The finding suggests its behavior is tantalizingly similar to that of the famous tool-using New Caledonian crow and has implications for the evolution of tool use and intelligence in birds.

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.

Perineuronal satellite neuroglia in the telencephalon of New Caledonian crows and other Passeriformes: evidence of satellite glial cells in the central nervous system of healthy birds?

Glia have been implicated in a variety of functions in the central nervous system, including the control of the neuronal extracellular space, synaptic plasticity and transmission, development and adult neurogenesis. Perineuronal glia forming groups around neurons are associated with both normal and pathological nervous tissue. Recent studies have linked reduction in the number of perineuronal oligodendrocytes in the prefrontal cortex with human schizophrenia and other psychiatric disorders.

New Caledonian crows learn the functional properties of novel tool types.

New Caledonian crows were presented with Bird and Emery's (2009a) Aesop's fable paradigm, which requires stones to be dropped into a water-filled tube to bring floating food within reach. The crows did not spontaneously use stones as tools, but quickly learned to do so, and to choose objects and materials with functional properties. Some crows discarded both inefficient and non-functional objects before observing their effects on the water level.

Context-dependent tool use in New Caledonian crows.

Humans and chimpanzees both exhibit context-dependent tool use. That is, both species choose to use tools when food is within reach, but the context is potentially hazardous. Here, we show that New Caledonian crows used tools more frequently when food was positioned next to a novel model snake than when food was positioned next to a novel teddy bear or a familiar food bowl.

Social learning in New Caledonian crows.

New Caledonian (NC) crows are the most sophisticated tool manufacturers other than humans. The diversification and geographical distribution of their three Pandanus tool designs that differ in complexity, as well as the lack of ecological correlates, suggest that cumulative technological change has taken place. To investigate the possibility that high-fidelity social transmission mediated this putative ratchet-like process, we studied the ontogeny of Pandanus tool manufacture and social organization in free-living NC crows.

Complex cognition and behavioural innovation in New Caledonian crows.

Apes, corvids and parrots all show high rates of behavioural innovation in the wild. However, it is unclear whether this innovative behaviour is underpinned by cognition more complex than simple learning mechanisms. To investigate this question we presented New Caledonian crows with a novel three-stage metatool problem.

Tool-making New Caledonian crows have large associative brain areas.

Animals with a high rate of innovative and associative-based behavior usually have large brains. New Caledonian (NC) crows stand out due to their tool manufacture, their generalized problem-solving abilities and an extremely high degree of encephalization. It is generally assumed that this increased brain size is due to the ability to process, associate and memorize diverse stimuli, thereby enhancing the propensity to invent new and complex behaviors in adaptive ways.

An investigation into the cognition behind spontaneous string pulling in New Caledonian crows.

The ability of some bird species to pull up meat hung on a string is a famous example of spontaneous animal problem solving. The "insight" hypothesis claims that this complex behaviour is based on cognitive abilities such as mental scenario building and imagination. An operant conditioning account, in contrast, would claim that this spontaneity is due to each action in string pulling being reinforced by the meat moving closer and remaining closer to the bird on the perch.

Causal reasoning in New Caledonian crows: Ruling out spatial analogies and sampling error.

A large number of studies have failed to find conclusive evidence for causal reasoning in nonhuman animals. For example, when animals are required to avoid a trap while extracting a reward from a tube they appear to learn about the surface-level features of the task, rather than about the task's causal regularities. We recently reported that New Caledonian crows solved a two-trap-tube task and then were able to immediately solve a novel, visually distinct problem, the trap-table task.

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.

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.

Spontaneous metatool use by New Caledonian crows.

A crucial stage in hominin evolution was the development of metatool use -- the ability to use one tool on another [1, 2]. Although the great apes can solve metatool tasks [3, 4], monkeys have been less successful [5-7]. Here we provide experimental evidence that New Caledonian crows can spontaneously solve a demanding metatool task in which a short tool is used to extract a longer tool that can then be used to obtain meat.

Parallel tool industries in New Caledonian crows.

Individual specialization in the use of foraging tools occurs in hunter-gatherer societies but is absent in non-human primate tool use. 'Parallel tool industries' in hunter-gatherers are mainly based on strict sexual division of labour that is highly reliant on social conformity. Here, we show that 12 individuals in a population of New Caledonian crows on Maré Island had strong preferences for either stick tools or pandanus tools.

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.

Design complexity and strength of laterality are correlated in New Caledonian crows' pandanus tool manufacture.

Population-level laterality is generally considered to reflect functional brain specialization. Consequently, the strength of population-level laterality in manipulatory tasks is predicted to positively correlate with task complexity. This relationship has not been investigated in tool manufacture.

The crafting of hook tools by wild New Caledonian crows.

The 'crafting' of tools involves (i) selection of appropriate raw material, (ii) preparatory trimming and (iii) fine, three-dimensional sculpting. Its evolution is technologically important because it allows the open-ended development of tools. New Caledonian crows manufacture an impressive range of stick and leaf tools.