An new paper in Nature Communications (Troscianko et al, 2012; see also the discussion at Not Exactly Rocket Science) suggests that the extraordinory extent of tool use by the New Caledonian crow (NCC) is accompanied by a morphology that differentiates them from other corvids. Specifically, a straight bill and a ever so slightly different position of their eyes enlarging their binocular sector, i.e. the part of the visual field where they have increase depth perception, allows them to follow what they’re doing with their tools much better than other crows, even when operating in narrow openings.
New Caledonian crows are famous for being habitual tool users and one of the best candidates, along with chimpanzees, for at least rudimentary cumulative cultural evolution of tool technology (Hunt and Gray, 2003) outside of humans, with tools serving the same function varying in complexity and production technique across their range, although their social structure, with young learning almost exclusively from their parents, and the finding that their population genetics is strongly structured (Rutz et al. 2012) makes it hard to entirely exclude a genetic basis for the geographic variance in tool sophistication.
Interestingly, while no other corvid comes close to displaying the extent of habitual tool use witnessed in the wild by NCCs, in controlled experimental settings other species such as rooks who have never been observed to use tools in the wild have demonstrated surprising capacities in spontanuously using and modifying tools to solve problems posed by the experimenter (Bird and Emery, 2009). This suggests that the cognitive capacities employed by tool using NCCs may not be unique to the species but part of a common corvid heritage of physical cognition and causal understanding. So what it is that translates those shared capacities into habitual action patterns in NCCs but not in their relatives?
While the resarch by Troscianko et al., as the authors make clear, does not answer the causal question of whether tool-use related selection pressures shaped their bill and eyes, or conversely whether their unusual morphology allowed New Caledonian crows’ to opportunistically exploit common capacities and tendencies in novel ways, it opens the way to an “embodied” approach to NCC tool use: What if the primary element, at least chronologically, in the package of behavioural and anatomical differences between today’s NCCs and other crows resides in their morphology? Incidentally, such an interpretation would very much parallel what Frederick Engels thought about the role of the hand in human prehistory 130-odd years ago.
Bird, Christopher D.and Nathan J. Emery, 2009. “Insightful problem solving and creative tool modification by captive nontool-using rooks”, PNAS 106 (25), pp. 10370-10375, DOI: 10.1073/pnas.0901008106
Hunt, Gavin R. and Russell D. Gray, 3003. “Diversification and cumulative evolution in New Caledonian crow tool manufacture”, Proc. R. Soc. Lond. B 270(1517) 867-874; DOI: 10.1098/rspb.2002.2302 1471-2954
Rutz, C., T. B. Ryder und R. C. Fleischer, 2012. “Restricted gene flow and fine-scale population structuring in tool using New Caledonian crows”, Naturwissenschaften 99(4), pp. 313-320, DOI: 10.1007/s00114-012-0904-6
Troscianko, Jolyon, Auguste M.P. von Bayern, Jackie Chappell, Christian Rutz, and Graham R. Martin, 2012. “Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows”, Nature Communications 3, Article number: 1110, October 9, 2012.