Clever crows memorise tool design

Publicly released, Friday 29 Jun 2018 

Certain tool designs seem to have stuck around in certain crow populations – suggesting crows pass on tool design through observation and memory.

Crows can make tools from memory

New Caledonian crows can recreate tools from memory according to a study in Scientific Reports. This ability may allow them to improve their own tools over time by recreating and then modifying other crows’ tools designs that they have memorised. Being able to recreate and modify items from memory is a trait rarely associated with non-human animals.

New Caledonian crows are known to make basic stick tools, hooked stick tools and barbed tools torn from the leaves of plants. However, so far it has not been clear if crows learn tool designs from other crows and if these designs improve over time. Although New Caledonian crows do not appear to closely observe or imitate the process of tool manufacture in the wild, specific tool designs made by crows living in different areas have persisted for at least several decades and improved over time, which suggests that the skill of tool making somehow spreads throughout crow populations. One idea of how tool design could be passed on and evolve is that individual crows use or observe other crows’ tools, remember a particular tool design, and then reproduce it to make their own tools.

To test the idea, Sarah Jelbert and colleagues trained eight crows to drop differently sized pieces of paper into a vending machine to retrieve rewards. Only pieces of a particular size were rewarded. Once the crows had been trained to recognize which sizes were rewarded, the authors provided them with a large piece of card but no physical templates of the previously rewarded paper sizes. The authors found that the crows tore up the card to form items that were similar in size to the pieces of paper that they had previously received a reward for. This indicates that these crows are able to form a mental image of their tool designs.

Additional information: The online version of the article in Scientific Reports can be found here.