New Caledonian crow
|New Caledonian Crow|
The New Caledonian Crow (Corvus moneduloides) is a tool-using species of crow endemic to New Caledonia. These crows are able to make hooks, an ability which not even humans' closest relative, the chimpanzee, has mastered. This species is not just famous for its tool-making abilities. These crows have also solved a number of sophisticated cognitive tests which suggest that this species is particularly intelligent Taylor et al. 2010, Taylor et al. 2012). Due to these findings this species 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 (Corvus moneduloides) is a moderately sized crow (40 cm 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 beak is of moderate size but is unusual in that the tip of the lower is angled up making it somewhat chisel-like in profile. It has been suggested that the beak evolved this morphology due to the selective pressures created by the need to hold a tool straight.
The voice is described as a soft "waa-waa" or "wak-wak", and sometimes as a hoarse "qua-qua" or "waaaark". Across New Caledonia the birds is often referred to as a 'qua-qua' due to its distinctive call.
Distribution and habitat
Ecology and behavior
It eats a very wide range of food, including many types of insects and other invertebrates (some caught in flight with some 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. It is known for using plant material to create stick and leaf tools. These tools can have naturally occurring barb incorporated into them, and can be actually fashioned into hooks. These tools are use for extracting large grubs from inside logs and branches, which have been shown to be an integral part of the crows' diet. This bird appears to fill the ecological niche of the woodpeckers and the Woodpecker Finch of the Galapagos, since the latter and New Caledonia lack woodpeckers. Unlike the Woodpecker Finch, however, it does not simply stab a grub and lever it slowly out of its log using a small twig but pokes the twig at the grub to agitate it into biting the twig. It shows great ingenuity in the search for food.
Its nest is built high in a tree with usually 2-3 eggs laid from September to November.
Tool use and manufacture
This species uses stick tools in the wild by finding small twigs and probing them into hole 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. These crows create hooks by crafting both wood and ferns into hooks. This is done by trimming the junctions between two branches or fern stolons into a tick shape (i.e. one junction has a long piece of wood/stolon attached, one junction has a small piece of wood /stolon attached) and then removing material from this junction to create a functioning hook. This imposition of three-dimensional form onto a natural material resembles carving. The only other species to exhibit hook tool manufacture is humans.
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. Gavin R. Hunt and colleagues at the University of Auckland studied tools the crows make out of pandanus (or screw pine) leaves:
Crows snip into the leaf edges and then tear out neat strips of vegetation with which they can probe insect-harboring crevices. These tools have been observed to come in three types: narrow strips, wide strips and multi-stepped strips—which are wide at one end and, via a manufacturing process that involves stepwise snips and tears, become narrow at the opposite end.
Observations of the distribution of 5,500 leaf counterparts or stencils left behind by the cutting process suggest that the narrow and the stepped tools are more advanced versions of the wide tool type. "The geographical distribution of each tool type on the island suggests a unique origin, rather than multiple independent inventions". This implies that the inventions, which involve a delicate change in the manufacturing process, were being passed from one individual to another.
The New Caledonian Crow also spontaneously makes tools from materials it does not encounter in the wild, the only non-human species known to do so. In 2002, researcher Alex Kacelnik and colleagues at the University of Oxford observed of a couple of New Caledonian Crows called Betty and Abel:
Betty's toolmaking abilities came to light by accident during an experiment in which she and Abel had to choose between a hooked and a straight wire for retrieving small pieces of pig heart, their favorite food. When Abel made off with the hooked wire, Betty bent the straight wire into a hook and used the tool to lift a small bucket of food from a vertical pipe. This experiment was the first time the crows had been presented with wire.
Subsequently, this ability was tested through a series of systematic experiments. Out of ten successful retrievals, Betty bent the wire into a hook nine times. Abel retrieved the food once, without bending the wire. The process would usually start with Betty trying to get the food bucket with the straight wire, but then she would make a hook from it bending it in different ways, usually by snagging one end of the wire under something, and then using the bent hook to pick up the tray.
Clearly, Betty's creation of hooks cannot be attributed to the shaping or reinforcement of trial-and-error behavior. In 2004, Gavin Hunt observed the crows in the wild also making hooks, but the adaptation to the new material of the wire was clearly novel, and also purposeful. This type of intentional tool-making, even if it is generalizing a prior experience to a completely new context, is rare in the animal world. Chimpanzees have great difficulty in similar innovative tasks.
The use of direct human activity has been recorded as well. This involves placing nuts in front of a vehicle on a heavy trafficked street, waiting for a car to crush it open and then waiting at pedestrian lights with other pedestrians to retrieve the crushed nut safely.
One such experiment, conducted by the Auckland team, involved putting food in a box out of the crows' reach. They were given a stick too short to reach the food, but they could use this to retrieve a longer stick from another box. The longer stick was then used to retrieve the food. This complex behaviour involved 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, and had previously only been observed in primates.
The crows also use tools to investigate potentially dangerous objects.
Some crows that were captured from the wild showed the ability to use mirrors to find objects they could not see with a direct line of sight. The birds tested did not immediately recognise themselves in the mirror, which may be due to their never having seen a mirror before. Individual crows showed different levels of ability.
- BirdLife International (2012). "Corvus moneduloides". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- Hunt, Gavin R. (January 1996). "Manufacture and use of hook-tools by New Caledonian crows". Nature 379 (6562): 249–251. doi:10.1038/379249a0.
- Weir, A.A.S., Chappell, J., & Kacelnik, A. (2002). "Shaping of hooks in New Caledonian crows". Science 297 (5583): 981. doi:10.1126/science.1073433. PMID 12169726.
- Taylor, Alex H.; Hunt, GR, Holzhaider, JC, Gray, RD (September 2007). "Spontaneous metatool use by New Caledonian crows". Current Biology 17 (17): 1504–1507. doi:10.1016/j.cub.2007.07.057. PMID 17702575. Retrieved 19 February 2013.
- Wimpenny, Joanna H.; Weir, AAS, Clayton, L, Rutz, C, Kacelnik, A (August 2009). "Cognitive Processes Associated with Sequential Tool Use in New Caledonian Crows". PLOS One 4 (8): e6471. doi:10.1371/journal.pone.0006471. PMC 2714693. PMID 19654861. Retrieved 19 February 2013.
- Rutz, Christian; Lucas A. Bluff; Nicola Reed; Jolyon Troscianko; Jason Newton; Richard Inger; Alex Kacelnik; Stuart Bearhop (17 September 2010). "The Ecological Significance of Tool Use in New Caledonian Crows". Science 329 (5998): 1523–1526. doi:10.1126/science.1192053. Retrieved 19 February 2013.
- Hunt, G.R. and Gray, R.D. (2004). "Direct observations of pandanus-tool manufacture and use by a New Caledonian crow (Corvus moneduloides)." (PDF). Animal Cognition 7 (2): 114–120. doi:10.1007/s10071-003-0200-0. PMID 15069611. Retrieved 3 May 2007.
- John Pickrell (23 April 2003). "Crows Better at Tool Building Than Chimps, Study Says". National Geographic News. Retrieved 3 May 2007.
- Robert Winkler (8 August 2002). "Crow Makes Wire Hook to Get Food". National Geographic News. Retrieved 3 May 2007.
- Red Light Runners BBC Nature
- Alex H. Taylor, Gavin R. Hunt, Jennifer C. Holzhaider and Russell D. Gray (2007). "Spontaneous Metatool Use by New Caledonian Crows". Current Biology 17 (In Press): 1504–7. doi:10.1016/j.cub.2007.07.057. PMID 17702575.
- Randerson, James (August 17, 2007). "Crows match great apes in skilful tool use". London: The Guardian. Retrieved 17 August 2007.
- Morelle, Rebecca (August 16, 2006). "Cleverest crows opt for two tools". BBC News. Retrieved 17 August 2007.
- Davies, Ella (14 January 2011). "Curious crows explore with tools". BBC News.
- "Crows use mirrors to find food". BBC Nature. 20 September 2011. Retrieved 19 May 2012.
- Oxford University crow research web site, including photos and movies
- From National Geographic: A video of the New Caledonian Crow making a hook out of wire (August 8, 2002)
- Tool use in crows is a combination of natural ability and schooling by other crows – LiveScience.com (October 31, 2006)
- BBC news website item about the New Caledonian Crow, includes video footage of tool use (August 16, 2007)
- Crow bends wire on purpose to lift bucket from glass tube (Nat'l Geo link no longer contains video).—YouTube