Some birds have memories like a steel trap (like remembering the days and times of garbage pickup in urban areas so they can swoop in and easily grab food). Now new research has demonstrated that super smart crows can actually recreate tools from memory, a capacity previously thought impossible for birds.
Crows are super smart—we knew that already. In addition to understanding causality and analogies, they can remember human faces, plan ahead, and hide their food from others. But crows are also known for their amazing tool-building skills, which they use to construct sticks, hooks, and barbs from plant material. New research published today in Scientific Reports suggests this ability, at least among New Caledonian crows (a particularly intelligent species of corvid), is more sophisticated than we thought, and that these birds are able to construct tools from memory.
In human societies, cultural evolution and tool building is an iterative process, whereby social traditions improve over time due to teaching, language, and imitation. But among New Caledonian crows, it’s not clear if their tool-making skills are the result of imitation, or an ability acquired through the passing down of cultural traditions. A going hypothesis is that tool designs are in fact culturally transmitted, and that it’s done through a process known as “mental template matching.”
Researchers Russell Grey from the University of Auckland, New Zealand, Sarah Jelbert from the University of Cambridge, along with colleagues from several other institutions, conducted an experiment that now provides the first evidence in support of this assertion.
The researchers trained eight crows to drop bits of paper into a vending machine, which the birds did to receive food rewards. The crows later learned that only cards of a specific size, either large pieces measuring 40 x 60 mm or small pieces measuring 15 x 25 mm, were rewarded. Once the crows were trained to recognize which sizes of paper tools resulted in a food reward, the scientists took all paper pieces away and replaced them with a single large sheet of paper that didn’t fit into the dispenser. Incredibly, the birds tore up the large card to create pieces that matched the size of the paper they previously used to earn rewards. The researchers called it “manufacture by subtraction.”
Importantly, the birds did not have visual access to any of the previous scraps of paper. The experiment suggests the birds held a mental image of the desired tool in their minds, which they used to construct the new tool. It also means some species of birds may have the ability to improve tools over time (something not proven in the study, but alluded to as a possibility), which they could do by recreating and then adjusting other designs they’ve seen and memorized. That’s an important consideration, because the ability to modify items from memory is typically associated with tool-making cultures, such as humans and some nonhuman primates.
Journal reference: S. A. Jelbert, R. J. Hosking, A. H. Taylor & R. D. Gray, Mental template matching is a potential cultural transmission mechanism for New Caledonian crow tool manufacturing traditions. Scientific Reports, volume 8, Article number: 8956 (2018). DOI: https://doi.org/10.1038/s41598-018-27405-1 Scientific journal article.