The New Caledonian crow (Corvus moneduloides) is a bird species found exclusively on the islands of New Caledonia and the Loyalty Islands in the Pacific Ocean. This medium-sized member of the crow family measures 40 centimeters. Its plumage is glossy black, often displaying iridescent hints of purple, dark blue, and green.
These crows possess a black bill, legs, and feet, with their bill conical and featuring a slightly chisel-shaped tip where the lower mandible angles upwards. Their habitat primarily consists of dense primary forests, though they can also be found in savannah environments.
Sophisticated Tool Crafting
New Caledonian crows exhibit remarkable abilities in crafting and using tools. They are known to fashion at least two distinct types of tools from plant materials: hooked-twig tools and serrated-edge tools made from pandanus leaves. These implements are primarily used for extracting hidden food, such as wood-boring beetle larvae, from crevices in decaying wood or vegetation.
The process of creating hooked-twig tools is intricate, involving a three-step sequence. Crows select branched twigs, trim them, and sculpt the hook using their beaks. This deliberate shaping allows them to create a functional hook that can snag prey. Once a tool is prepared, the crow often pokes it into a burrow to agitate the larva, causing it to bite onto the tool, which the crow then withdraws.
Pandanus leaf tools demonstrate an understanding of material properties. Crows rip barb-edged pandanus leaves, cutting and tearing them to produce specific designs, including uniformly wide, narrow, and complex stepped or tapered shapes. The tapered design involves multiple cuts and rips to create a tool that is stiff at the base for grip and progressively thinner and more flexible at the working end.
Advanced Cognitive Abilities
The sophisticated tool-making and use observed in New Caledonian crows are underpinned by remarkable cognitive capabilities. Their understanding of cause-and-effect, known as causal reasoning, has been demonstrated through various experiments. One such test is the “Aesop’s Fable” where crows are presented with a tube of water containing a floating food reward out of reach.
In these experiments, crows learn to drop objects into the water to raise the level and bring the food within reach. They prefer to drop objects into water-filled tubes over sand, sinking objects over floating, and solid items instead of hollow. Their performance in these water displacement tasks, which also includes favoring tubes with a higher starting water level, indicates a causal understanding comparable to that of a 5 to 7-year-old child.
These crows also exhibit planning for future needs through “meta-tool use.” They use one tool to acquire another, then utilize that second tool to retrieve a reward. For example, a crow might use a short stick to extract a longer stick from a container, then use the longer stick to reach food. This multi-stage behavior, even when sub-goals are not immediately visible, provides evidence of their capacity for sequential planning and understanding of means-end relationships.
Cultural Transmission of Skills
The complex tool-making skills of New Caledonian crows are not innate; they are influenced by social learning and passed down. Young crows spend periods observing parents and other adults, a learning process that can take over a year before achieving adult proficiency in tool manufacture. This observational learning helps maintain these intricate behaviors within the population.
Parents facilitate this learning by demonstrating tool use and leaving discarded tools or “counterparts”—the impressions left on pandanus leaves after a tool has been cut—which juveniles may use as templates. This “vertical transmission” of knowledge, primarily from parent to offspring, plays a role in replicating specific tool designs. The social structure of these crows, which favors this direct lineage learning, helps to preserve local tool-making traditions.
Evidence of this cultural transmission is supported by regional variations in tool designs across populations. Specific shapes of pandanus leaf tools, such as wide, narrow, or stepped designs, show distinct geographical distributions. These variations are not linked to ecological differences, suggesting they represent local “traditions” or “dialects” of tool design, indicative of cumulative cultural evolution.