The New Caledonian crow (Corvus moneduloides) is an all-black, medium-sized member of the family Corvidae, native to New Caledonia. The bird is often referred to as the 'qua-qua' due to its distinctive call. The New Caledonian crow sometimes captures grubs in nooks or crevices by poking a twig at the grub to agitate it into biting the twig, which the crow then withdraws with the grub still attached. This method of feeding indicates the New Caledonian crow is capable of tool use. They are able to make hooks. This species is also capable of solving a number of sophisticated cognitive tests which suggest that it is particularly intelligent. As a result of these findings, the New Caledonian crow has become a model species for scientists trying to understand the impact of tool use and manufacture on the evolution of intelligence.
The New Caledonian crow is a moderate-sized crow, (15.7 inches in length) similar in size to the house crow but less slender-looking. The bird has an all-black appearance with a rich gloss to its feathers of purple, dark blue and some green in good light. The beak, feet and legs are all black. The vocalization is described as a soft "waa-waa" or "wak-wak", and sometimes as a hoarse "qua-qua" or "waaaark". Across New Caledonia, the bird is often referred to as a 'qua-qua' due to its distinctive call.
The beak is moderate in size but is unusual in that the tip of the lower mandible is angled upwards, making it somewhat chisel-like in profile. It has been suggested that this beak morphology evolved due to the selective pressure of needing to hold a tool straight.
This bird is endemic to the islands of New Caledonia in the Pacific, living in primary forest. It inhabits only the main island, Grande Terre, and one of the Loyalty Islands, Maré Island.
The New Caledonian crow eats a wide range of food, including many types of insects and other invertebrates (some caught in flight with great agility, including night-flying insects which it catches at dusk), eggs and nestlings, small mammals, snails (which it drops from a height onto hard stones), and various nuts and seeds.
This species uses stick tools in the wild by finding small twigs and probing them into holes in logs to extract insects and larvae. New Caledonian crows are also able to manufacture tools by breaking twigs off bushes and trimming them to produce functional stick tools. Tool manufacture is rare in comparison to simple tool use and indicates a higher level of cognitive function. The crows can also make leaf tools by tearing rectangular strips off the edges of Pandanus spp. leaves. The creation of such leaf tools allows these crows to exploit naturally occurring hooks – the barbs running along the edges of these leaves can be used as hooks if the tool is held such that the barbs point towards the crows’ head. Other naturally occurring hooks are also incorporated within tools, such as the thorns that grow on vine species in New Caledonia.
The New Caledonian crow is the only non-primate species for which there is evidence of cumulative cultural evolution in tool manufacture. That is, this species appear to have invented new tools by modifying existing ones, then passing these innovations to other individuals in the cultural group. The New Caledonian crow also spontaneously makes tools from materials it does not encounter in the wild. Intentional tool manufacture, even if it is generalizing a prior experience to a novel context, is rare in the animal world.
Meta-tool use is using one tool on another tool to achieve the objective of the task. It is generally considered to be a behaviour requiring more complex cognitive ability than the use of just a single tool. Studies show that New Caledonian crows are capable of meta-tool use, at a level rivalling the best performances seen in primates. One such study involved putting food in a box out of the crows' reach. The crows were given a stick that was too short to reach the food. However, this short stick could be used to retrieve a longer stick from another box, which could then be used to retrieve the food. This complex behaviour involved the crow realising that a tool could be used on non-food objects, and suppressing the urge to go directly for the food. It was solved by six of seven birds on the first attempt. This behaviour had previously only been observed in primates.
In a study conducted at the Max Planck Society crows have been shown to create compound tools from 2-4 short branches that could be slotted together.
New Caledonian crows have shown they are able to process information from mirrors, a cognitive ability possessed by only a small number of species. By using a mirror, wild-caught New Caledonian crows are able to find objects they cannot see with a direct line of sight. However, the crows were unable to recognise themselves in the mirror - other corvids have tested positive for this capability.
