Christopher Bird and Nathan Emery (2009) performed a number of tool use experiments on rooks -- birds related to crows (corvids) that do not use tools in the wild. Some other corvids, in particular New Caledonian crows, are expert tool users. People who work with New Caledonian crows compare their tool prowess with the great apes -- they can manufacture novel implements, put together two items into a compound tool, and use tools to make other tools. Each of these is a test that psychologists devised to differentiate human tool manufacture from animals. In each case, apes passed, and then the New Caledonian crows passed.
In the current paper, Bird and Emery find that rooks also can do these things, despite never having been observed to do any of them in the wild. They conclude that the birds likely do not have specialized cognitive adaptations for tool manufacture, but instead that they are solving novel problems using cognitive skills that are also useful for many other kinds of problems -- in short, domain general cognition:
Our results contradict suggestions that tool use was the driving force behind the evolution of advanced physical intelligence (2). It appears more likely that corvid tool use is a useful by-product of a domain-general “cognitive tool-kit” (31) rather than a domain-specific ability that evolved to solve tool related problems. Whether or not each species taps into this capacity for tool use may depend on their ecology (22, 32).
In hominoids, a shared basic ability for tool manufacture goes back at least to the Middle Miocene, based on its phylogenetic distribution. It is an open question whether early apes also were tool users. Some monkeys make and use tools in the wild, and if their abilities are homologous with ours, that would put the cognitive capacity for tool manufacture back into the Oligocene. Bird and Emery go through a similar train of logic for the corvids:
Rooks are highly innovative, social foragers (39), using their cognitive abilities in a number of nontool related ways (40). Our findings provide further support for recent claims of convergent evolution in the cognitive abilities of corvids and apes (31). New Caledonian crows and now rooks have been shown to rival, and in some cases outperform, chimpanzees in physical tasks, leading us to question our understanding of the evolution of intelligence.
The claim is that the cognitive resources useful for tool manufacture are probably also useful for other things, and therefore conserved in many if not all corvids. If they're useful for other things, there's no necessary reason for them to have evolved as adaptations for tool use or manufacture (although tool use in ancestral corvids remains possible). The same may be true of primates. For example, gorillas process some kinds of plant foods in complicated ways, using series of steps comparable in complexity to chimpanzee tool manufacture. But gorillas use tools very sporadically in the wild. Arguably, general-purpose cognitive abilities underlie both kinds of activities -- and social learning would facilitate both kinds of skills.
References:
Bird CD, Emery NJ. 2009. Insightful problem solving and creative tool modification by captive nontool-using rooks. Proc Nat Acad Sci USA 106:10370-10375. doi:10.1073/pnas.0901008106
