Jennifer C. Holzhaider

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. Six out of the seven crows initially attempted to extract the long tool with the short tool. Four successfully obtained meat on the first trial. The experiments revealed that the crows did not solve the metatool task by trial-and-error learning during the task or through a previously learned rule. The sophisticated physical cognition shown appears to have been based on analogical reasoning. The ability to reason analogically may explain the exceptional tool-manufacturing skills of New Caledonian crows.

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. We presented experienced and naïve New Caledonian crows with a novel, visually restricted string-pulling problem that reduced the quality of visual feedback during string pulling. Experienced crows solved this problem with reduced efficiency and increased errors compared to their performance in standard string pulling. Naïve crows either failed or solved the problem by trial and error learning. However, when visual feedback was available via a mirror mounted next to the apparatus, two naïve crows were able to perform at the same level as the experienced group. Our results raise the possibility that spontaneous string pulling in New Caledonian crows may not be based on insight but on operant conditioning mediated by a perceptual-motor feedback cycle.

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. We found that juvenile crows took more than 1 year to reach adult proficiency in their Pandanus tool skills. Although trial-and-error learning is clearly important, juveniles have ample opportunity to learn about Pandanus tool manufacture by both observing their parents and interacting with artifactual material. The crows’ social system seems likely to promote the faithful social transmission of local tool designs by both favoring the vertical transmission of tool information and minimizing horizontal transmission. We suggest that NC crows develop their Pandanus tool skills in a highly scaffolded learning environment that facilitates the cumulative technological evolution of tool designs.

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.

The social structure of New Caledonian crows

New Caledonian (NC) crows, Corvus moneduloides, have impressive tool-manufacturing and tool-using skills in the wild, and captive birds have displayed exceptional cognitive abilities in experimental situations. However, their social system is largely unknown. In this study we investigated whether the social structure of NC crows might have had a role in the development of their cognitive skills. We observed crows in their natural habitat on the island of Mare, New Caledonia, and estimated their social network size based on tolerance to family and nonfamily crows at feeding tables. Our ! ndings suggest that NC crows are not a highly social corvid species. Their core unit was the immediate family consisting of a pair and juveniles from up to two consecutive breeding years. Pairs stayed together year round, and were closely accompanied by juveniles during their ! rst year of life. Parents were highly tolerant of juveniles and sometimes continued to feed them well into their second year. NC crows predominantly shared feeding tables with immediate family. Of the nonfamily crows tolerated, juveniles were overrepresented. The main mechanism for any social transmission of foraging skills is likely to be vertical (from parents to offspring), with only limited opportunity for horizontal transmission. The social organization we found on Mare is consistent with the idea that NC crows’ multiple pandanus tool designs on mainland Grande Terre are an example of cumulative technological evolution.

Innovative pandanus-tool folding by New Caledonian crows

The ratcheting of evolutionary innovations over time has enabled humans to produce complex technology. This process requires (1) technological innovations, (2) the accurate transmission of innovations by social learning, and (3) the faithful maintenance of new technology by its standardised reproduction. Although nonhuman primates are good behavioural innovators, there is no evidence that they have evolved cumulative technology. It has been previously suggested that New Caledonian crows have made cumulative changes to their pandanus tool manufacture. However, technological innovation by individual New Caledonian crows in the wild had not been observed. Here, we report that two distantly related male crows at the same location have a novel way of using pandanus tools by first folding them into a boomerang-like shape. The fine manipulation to fold tools was highly routinised and its two main manipulatory components (direction of head movement and holding technique) were exclusively lateralised. As a consequence the fold arrangement was invariable irrespective of a tool’s position before folding. The males’ tool-folding confirms that New Caledonian crows have a disposition to routinise and lateralise complex sequences of manipulatory actions. Such a disposition may facilitate the evolution of cumulative technology because it can act to standardise the reproduction of a technological innovation.