On a small Pacific island off the coast of Australia, there live crows who craft and use hooks. This is no small feat, as New Caldonian crows, the species of crow found only on this island, are the only other animal besides humans known to manufacture hooked tools. While humans use hooks for tasks ranging from fishing to crochet, New Caledonian crows use hooks as foraging tools to extract prey from logs and trees up to 13 times faster than they would with straight tools (St Clair et al., 2018). Crows make these hooks by trimming and sculpting the twigs of one special plant known as wild tantan colloquially and Desmanthus virgatus scientifically (Hunt et al., 2004).
Hooked grub diggers can look to humans like the crow equivalent of a luxury sports car: expensive to acquire, rare, ripe for theft, but a fast and smooth ride. The value of a hooked tool is obvious to us. But what about to the crows? Do they value their hooks? According to a December 2021 eLife study, the answer is yes (Klump et al. 2021).
Unfortunately, we can’t ask animals what they value; so scientists use experimental proxies to determine animal perceptions of value. In these experiments, animals are trained to trade food, tokens, or other items of varying values for the object of interest. This takes a long time and cannot be done with wild animals. The researchers in the recent eLife study, however, developed a new system to measure animal values by experimentally measuring crow preference and safekeeping of tools.
The researcher’s experiment was done in two acts. First, they tested whether crows show a preference for hooked tools. They offered 20 non-hooked tools, 1 hooked tool, and a log with grub to motivate foraging to temporarily captured wild New Caledonian crows. The crows much preferred the hooked tool, transporting and deploying it nearly 90% of the time.
Interestingly, when the scientists threw a spoke in the crow’s wheel by making all but one of the non-hooked tools from the special plant used by crows for hooks, Desmanthus virgatus, the crows were slightly less likely to transport and use the hooked tools. In response to this finding, the scientists conjecture that the crows perhaps use a “rule of thumb” and initially pay attention to material rather than shape. To offer a human equivalent, this would be like walking into a clothing store and looking for leather before looking for a leather jacket.
In their second act, the researchers experimentally measured how and how often the crows safekept hooked tools as compared to non-hooked ones. The researchers already knew that crows take care of their tools and especially so at high elevations when it is extra costly to retrieve a tool (Klump et al., 2015). Crows aren’t the only animals who safekeep their tools: otters, chimpanzees, and Galapagos woodpecker finches do too. Safekeeping can reduce the risk of a tool being stolen or lost and thus the risk that it would need to be replaced, which can take precious time and energy.
The researchers’ second experiment was similar to the first: they offered a selection of tools and two food logs to the crows, then waited and watched for safekeeping behavior. As it turns out, crows take very good care of their things. On average, they stored their tools in holes or underfoot more than 90% of the time. However, the crows were much more likely to store Desmanthus virgatus hooked tools than non-hooked tools. Indeed, they safekept the hooked tools made from the special plant 95% of the time but the non-hooked tools only 87% of the time. This is unsurprising to anyone with a precious family heirloom wrapped in paper towels and bubble wrap in their attic but day-to-day dishes stacked in the sink.
The mode of safekeeping also differed based on the type of tool. The crows stored their hooks in holes much more often than non-hooked tools, no matter the material. This might be because storage in holes is safer but it also may play a role in functionality. Storing hooked tools in a hole ensures the hook is always picked up in the proper orientation (that is, non-hooked end held and hooked end ready to wield).
The storage of tools is a big deal, as it allows for reuse and revision which might contribute to the eventual building of cultural technological advancements. This accumulation of knowledge is only known to occur in chimpanzees, New Caledonian crows, and humans. So, it turns out taking care of our things might be a key ingredient for innovation.
New Caledonian crows’ selection and storage of hooked tools found in this recent study suggests they value them. This valuation might stem from hooks’ effectiveness, required investment, or perhaps some other reason only the crows know. No matter what, we still have much to learn from these clever creatures and their complex creations.
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