Use of tools in New Caledonian crows

If men had wings and bore black feathers,
few of them would be clever enough to be crows
(Henry Beecher, 1850)².

An interesting aspect of behavior is its flexibility that helps organisms to adapt to new challenges in their ecological niches. One of the most interesting types of behaviors is the use of tools by some groups in the animal kingdom.

Primates are considered to be the most developed and multifaceted tool users, but observations of New Caledonian crows (Corvus moneduloides) suggest that these birds may rival nonhuman primates in cognitive abilities related to the use of tools.

The article Shaping of hooks in New Caledonian crows (Weir, A.A.S., et al, 2002)³, really stirred up emotions when it was published as it was one of the first proofs of tool manufacture in non primates animals.

The following paragraphs discus the different aspects of tool use and manufacture in new Caledonian crows with a special emphasis on the aspect of learning. I will first introduce the specie. The next part will focus on tool use of the Caledonian crows followed by a description of the scientists observations³. The following part will focus on the special ability of those crows to not only use tools but to also manufacture them. The last part of this essay will focus on the learning ability of new Caledonian crows and the incremental progresses that can be compared to human progress in technology.

New Caledonian Crow

The crow is a bird of the worldwide family Corvidae. It can be a common name for the whole family, or just for the 40 species of the genus Corvus.⁴

The New Caledonian Crow (Corvus moneduloides) is a moderately sized (40 cm in length) similar in size to the House Crow but less slender looking. The bird is all black with a rich gloss to the feathers of purple, dark blue and some green in good light. The bill, feet and legs are all black too. The bill is of moderate size but is unusual in that the tip of the lower is angled up making it somewhat chisel-like in profile. The bird is endemic to the island of New Caledonia and the Loyalty Islands in the Pacific, living in primary forest. The nest is built high in a tree with usually only 2 eggs laid from September to November. The voice is described as a soft waa-waa or wak-wak, sometimes a hoarse waaaaw.

It takes a very wide range of food items including many types of insects and other invertebrates, eggs and nestlings, snails, and various nuts and seeds. It is one of the most remarkable and resourceful of creatures, showing great ingenuity in the search for food.⁵

Shaping of Hooks in New Caledonian Crows an example of tool use and manufacturing ³:

New Caledonian crows are known to make and use complex tools in the wild from number of different materials. Caledonian crows have exceptional skill and flexibility when using and making tools, even when novel materials are involved, and use techniques which would not work with natural materials to use it for particular task. This interesting phenomenon of tool use is well demonstrated in an observation made by Weir, Chappell, and Kacelnik (2002), where a captive female spontaneously bent a piece of straight wire into a hook and successfully used it to lift a bucket containing food from a vertical pipe.

To investigate the importance of this observation several new trials were conducted on a couple of crows. A single straight piece of wire was placed on top of tube containing food, without any intervention until either of the birds obtained the food (valid) or dropped the wire irretrievably into the tube (invalid). Out of 10 valid trials the female bent the wire and used it to retrieve the food nine times, and the male retrieved the food once with the straight wire.

To bend the wire, she first wedged one end of it in sticky tape or held it in her feet at a location 3 meter from the food, where there was no tape. She then pulled the other end orthogonally with her beak, resulting in a bend with an angle of 44-104°. She started to bend the wire 35+/-8 seconds after the start of each trial and used the resulting hook 6+/-2 seconds later. In all valid trials, the birds retrieved the food within 2 minutes.

The method used by the female crow is different from those previously reported and would be unlikely to be effective with natural materials. Purposeful modification of objects by animals for use as tools, without extensive prior experience, is almost unknown.

The conclusion of these observations, in a nonhuman/primate species, raises numerous questions about the conditions set before these animals causing them to generate cognitive abilities superior to other organisms of their kind.

Tool manufacture¹:

Crows make two distinct types of tools: stick-type tools and pandanus-leaf tools. Stick-type tools consist of lengths of a range of relatively stiff raw materials. The materials identified so far are twigs, bamboo stems, fern stolons, compound leaf stems, a slither removed from the stem of a palm leaflet and leaf petioles. Pandanus tools, on the other hand, are very flexible lengths of material that crows cut and rip from the leaves of monocot trees. Both ways are common and widespread.

More involved manufacture is required to make hooked tools. Birds may also simply pick up petioles and dead twigs from the ground to use as tools without modifying them. In contrast, all pandanus tools are manufactured.

Crows have developed two distinct groups of stick-type tools: hooked tools and non-hooked tools. All these tools are stiff and stick-like in nature. Hooked-twig tools most probably represent the population-level diversification of stick-type tools.

The case for diversification of pandanus tools is stronger. A survey of tool counterparts showed that crows manufacture three distinct pandanus-tool designs: wide tools, narrow tools and stepped tools.

There are three varieties of hooked stick-type tools: one from twigs, one from the thorny stems of compound leaves of a leguminous vine (Caesalpinia schlechteri) and one from the stolons of a Nephrolepis species fern. A material-specific technique is required to make each of these three varieties. Hooked-twig tool manufacture is by far the most complex because it involves the creation of a hook where none was present.

Crows select material that has naturally-occurring hooks. Crows also select specific tree species when they choose material to make a hooked-twig tool. Two main trees are known to be used - Elaeocarpus dognyensis and Cunonia vieillardii. The advantages of using E. dognyensis and C. vieillardii are not known, but these trees have an abundance of forked twigs that are suitable for making hooked-twig tools. Crows also use the common, tougher-leafed pandanus trees for toolmaking to a relatively greater extent than the less common, more fragile-leafed trees.

Crows appear to have developed different tools and associated manufacture techniques to meet site-specific foraging needs.

The hook tools that crows make out of live twigs often have pointed hooks on their wide ends. These hooks cannot be created by simply pulling twigs off adjoining stems. The hooks on hooked-twig tools are sculpted from the stumps of adjoining stems, which birds sharpen and refine with their bills.

The manufacture of crows' stepped pandanus tools is lateralized. Numerous observations found that birds preferred to make these tools on the left edges of leaves rather than the right edges. Scientists speculate that the left-edge bias might be caused by the general specialization in animals of the right-eye/left-hemisphere system for complex sequential tasks, this was not established experimentally.

Learning abilities and incremental progresses¹:

Many of the specialized aspects that crows have in their tool-making are only known to be associated with cultural behaviors in humans. The nature of crows' tool manufacture raises the possibility that its complexity may be the consequence of a well-developed understanding of the real world. There is also positive circumstantial evidence that transmission of tool know-how in crows involves social learning.

Pandanus-tool manufacture appears to meet criteria used to identify traditional behavior. The shapes of pandanus tools are generally quite similar at individual sites compared to shape differences between sites, the compliment of pandanus-tool designs differs between sites in ways that suggest they have a common historical origin and the shape variation in a pandanus-tool design and its absence from a site lacks an obvious ecological explanation.

Finally, it is quite plausible that both individual and social learning are involved in the development of crows tool manufacture, taking into account the fact that Corvus species share some characteristics with primates. These shared characteristics include highly encephalized areas of the brain that seem to deal with so called 'intelligent' behavior (Rehkämper and Zilles 1991), behavioral flexibility and considerable cognitive capabilities (Heinrich 1995, Zorina 1997, Fritz and Kotrschal 1999), and generally social species that can provide substantial amounts of parental care to offspring (Heinrich 1999).

1. Hunt, G.R. and Gray, R.D. (in press). Tool manufacture by New Caledonian crows: chipping away at human uniqueness. Proceedings of the 23rd International Ornithological Congress. From website: http://language.psy.auckland.ac.nz/crows/files/IOC_beijing.pdf.

2. Rev. Henry Beecher, ca. (1850). From website: http://language.psy.auckland.ac.nz/crows/

3. Weir, A.A.S., Chappell, J., & Kacelnik, A. (2002). Shaping of hooks in New Caledonian crows. Science 297: 981. From website: http://users.ox.ac.uk/~kgroup/tools/links.shtml

4. http://www.reference.com/browse/crystal/8611

5. http://www.reference.com/browse/wiki/New_Caledonian_Crow

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Use of tools in New Caledonian crows If men had wings and bore black feathers, few of them would be clever enough to be crows (Henry Beecher, 1850)². An interesting aspect of behavior is its flexibility that helps organisms to adapt to new challenges in their ecological niches. One of the most interesting types of behaviors is the use of tools by some groups in the animal kingdom. Primates are considered to be the most developed and multifaceted tool users, but observations of New Caledonian crows (Corvus moneduloides) suggest that these birds may rival nonhuman primates in cognitive abilities related to the use of tools. The article Shaping of hooks in New Caledonian crows (Weir, A.A.S., et al, 2002)³, really stirred up emotions when it was published as it was one of the first proofs of tool manufacture in non primates animals. The following paragraphs discus the different aspects of tool use and manufacture in new Caledonian crows with a special emphasis on the aspect of learning. I will first introduce the specie. The next part will focus on tool use of the Caledonian crows followed by a description of the scientists observations³. The following part will focus on the special ability of those crows to not only use tools but to also manufacture them. The last part of this essay will focus on the learning ability of new Caledonian crows and the incremental progresses that can be compared to human progress in technology. New Caledonian Crow The crow is a bird of the worldwide family Corvidae. It can be a common name for the whole family, or just for the 40 species of the genus Corvus.⁴ The New Caledonian Crow (Corvus moneduloides) is a moderately sized (40 cm in length) similar in size to the House Crow but less slender looking. The bird is all black with a rich gloss to the feathers of purple, dark blue and some green in good light. The bill, feet and legs are all black too. The bill is of moderate size but is unusual in that the tip of the lower is angled up making it somewhat chisel-like in profile. The bird is endemic to the island of New Caledonia and the Loyalty Islands in the Pacific, living in primary forest. The nest is built high in a tree with usually only 2 eggs laid from September to November. The voice is described as a soft waa-waa or wak-wak, sometimes a hoarse waaaaw. It takes a very wide range of food items including many types of insects and other invertebrates, eggs and nestlings, snails, and various nuts and seeds. It is one of the most remarkable and resourceful of creatures, showing great ingenuity in the search for food.⁵ Shaping of Hooks in New Caledonian Crows an example of tool use and manufacturing ³: New Caledonian crows are known to make and use complex tools in the wild from number of different materials. Caledonian crows have exceptional skill and flexibility when using and making tools, even when novel materials are involved, and use techniques which would not work with natural materials to use it for particular task. This interesting phenomenon of tool use is well demonstrated in an observation made by Weir, Chappell, and Kacelnik (2002), where a captive female spontaneously bent a piece of straight wire into a hook and successfully used it to lift a bucket containing food from a vertical pipe. To investigate the importance of this observation several new trials were conducted on a couple of crows. A single straight piece of wire was placed on top of tube containing food, without any intervention until either of the birds obtained the food (valid) or dropped the wire irretrievably into the tube (invalid). Out of 10 valid trials the female bent the wire and used it to retrieve the food nine times, and the male retrieved the food once with the straight wire. To bend the wire, she first wedged one end of it in sticky tape or held it in her feet at a location 3 meter from the food, where there was no tape. She then pulled the other end orthogonally with her beak, resulting in a bend with an angle of 44-104°. She started to bend the wire 35+/-8 seconds after the start of each trial and used the resulting hook 6+/-2 seconds later. In all valid trials, the birds retrieved the food within 2 minutes. The method used by the female crow is different from those previously reported and would be unlikely to be effective with natural materials. Purposeful modification of objects by animals for use as tools, without extensive prior experience, is almost unknown. The conclusion of these observations, in a nonhuman/primate species, raises numerous questions about the conditions set before these animals causing them to generate cognitive abilities superior to other organisms of their kind. Tool manufacture¹: Crows make two distinct types of tools: stick-type tools and pandanus-leaf tools. Stick-type tools consist of lengths of a range of relatively stiff raw materials. The materials identified so far are twigs, bamboo stems, fern stolons, compound leaf stems, a slither removed from the stem of a palm leaflet and leaf petioles. Pandanus tools, on the other hand, are very flexible lengths of material that crows cut and rip from the leaves of monocot trees. Both ways are common and widespread. More involved manufacture is required to make hooked tools. Birds may also simply pick up petioles and dead twigs from the ground to use as tools without modifying them. In contrast, all pandanus tools are manufactured. Crows have developed two distinct groups of stick-type tools: hooked tools and non-hooked tools. All these tools are stiff and stick-like in nature. Hooked-twig tools most probably represent the population-level diversification of stick-type tools. The case for diversification of pandanus tools is stronger. A survey of tool counterparts showed that crows manufacture three distinct pandanus-tool designs: wide tools, narrow tools and stepped tools. There are three varieties of hooked stick-type tools: one from twigs, one from the thorny stems of compound leaves of a leguminous vine (Caesalpinia schlechteri) and one from the stolons of a Nephrolepis species fern. A material-specific technique is required to make each of these three varieties. Hooked-twig tool manufacture is by far the most complex because it involves the creation of a hook where none was present. Crows select material that has naturally-occurring hooks. Crows also select specific tree species when they choose material to make a hooked-twig tool. Two main trees are known to be used - Elaeocarpus dognyensis and Cunonia vieillardii. The advantages of using E. dognyensis and C. vieillardii are not known, but these trees have an abundance of forked twigs that are suitable for making hooked-twig tools. Crows also use the common, tougher-leafed pandanus trees for toolmaking to a relatively greater extent than the less common, more fragile-leafed trees. Crows appear to have developed different tools and associated manufacture techniques to meet site-specific foraging needs. The hook tools that crows make out of live twigs often have pointed hooks on their wide ends. These hooks cannot be created by simply pulling twigs off adjoining stems. The hooks on hooked-twig tools are sculpted from the stumps of adjoining stems, which birds sharpen and refine with their bills. The manufacture of crows' stepped pandanus tools is lateralized. Numerous observations found that birds preferred to make these tools on the left edges of leaves rather than the right edges. Scientists speculate that the left-edge bias might be caused by the general specialization in animals of the right-eye/left-hemisphere system for complex sequential tasks, this was not established experimentally. Learning abilities and incremental progresses¹: Many of the specialized aspects that crows have in their tool-making are only known to be associated with cultural behaviors in humans. The nature of crows' tool manufacture raises the possibility that its complexity may be the consequence of a well-developed understanding of the real world. There is also positive circumstantial evidence that transmission of tool know-how in crows involves social learning. Pandanus-tool manufacture appears to meet criteria used to identify traditional behavior. The shapes of pandanus tools are generally quite similar at individual sites compared to shape differences between sites, the compliment of pandanus-tool designs differs between sites in ways that suggest they have a common historical origin and the shape variation in a pandanus-tool design and its absence from a site lacks an obvious ecological explanation. Finally, it is quite plausible that both individual and social learning are involved in the development of crows tool manufacture, taking into account the fact that Corvus species share some characteristics with primates. These shared characteristics include highly encephalized areas of the brain that seem to deal with so called 'intelligent' behavior (Rehkämper and Zilles 1991), behavioral flexibility and considerable cognitive capabilities (Heinrich 1995, Zorina 1997, Fritz and Kotrschal 1999), and generally social species that can provide substantial amounts of parental care to offspring (Heinrich 1999). 1. Hunt, G.R. and Gray, R.D. (in press). Tool manufacture by New Caledonian crows: chipping away at human uniqueness. Proceedings of the 23rd International Ornithological Congress. From website: http://language.psy.auckland.ac.nz/crows/files/IOC_beijing.pdf. 2. Rev. Henry Beecher, ca. (1850). From website: http://language.psy.auckland.ac.nz/crows/ 3. Weir, A.A.S., Chappell, J., & Kacelnik, A. (2002). Shaping of hooks in New Caledonian crows. Science 297: 981. From website: http://users.ox.ac.uk/~kgroup/tools/links.shtml 4. http://www.reference.com/browse/crystal/8611 5. http://www.reference.com/browse/wiki/New_Caledonian_Crow

Notes (if any) by Peter Kabai: