I got an e-mail asking about we recognise true tool use in animals. For me, two factors are the most important: flexible behaviour, and problem-solving. Both are linked: problem-solving requires flexible behaviour to be implemented.
To demonstrate this, I will use the woodpecker finch, Cactospiza pallida, one of Darwin’s finches from the Galápagos. They grab cactus spines and twigs in their beaks and use them to get their arthropod prey out of crevices. We know that this is really dynamic tool use that comes out of a cognitive thought pattern, rather than being a hardwired behaviour, because of two observations.
- If needed, they will shorten twigs or smooth them out.
- Tebbich et al. (2002) find that tool use only happens in arid areas, where prey mostly hides in tree holes, whereas tool use in humid areas where arthropods hang out in the open was negligible to non-existent.
In other words, the process involved in tool use in the woodpecker finch is problem-solving, not just a triggered instinct – this is why they modify their sticks, and why they even use the tool only in arid areas where it’s necessary. And both points automatically imply a flexible behaviour that allows the woodpecker finch to adapt cognitively to new environments and challenges.
Some people also place social learning as a criterion, based on numerous reports of the knowledge of tool use being passed on culturally by observation. However, I consider this an unnecessary limitation: there is no reason to discount solitary, non-social species. It may be that current research is just focused on typical examples (birds, primates), where social observation is commonplace, and that further research will uncover many examples of tool use from solitary species that are simply clever enough to solve problems on their own, without having observed the solution from tribe-mates before.
On a related note, I got an alert about this soon-to-be-released Cambridge University Press book, Tool Use in Animals: Cognition and Ecology, edited by Sanz, Call & Boesch. Given that these three are all leading primatologists, it comes as no surprise that 9/13 chapters deal with primate tool use. The title is thus a bit deceptive given that tool use is definitely known from other mammals, from birds, and from insects, but it seems like a good compilation of chapters nonetheless (and one can’t judge it without having read it first!).