A new study has shown that crows can value their tools, just like us.
“A lot of us will take care of a brand new phone, making sure it doesn’t get scratched, dropped or lost. But we can handle an old phone with a cracked screen quite carelessly,†Barbara said. Klump, behavioral ecologist, now at the Max Planck Institute. , Germany.
New Caledonian crows (Corvus moneduloides) are so renowned for their intelligence that scientists use them as a model species to help understand the evolution of tool use and associated behaviors like planning.
Not only can these intelligent crows use found objects as tools, but they can also shape or even construct them from multiple pieces that are individually unnecessary – something previously only seen in primates.
In the wild, they use these twig tools, neatly held in their beaks, to annoy larvae safely hidden in tree crevices. The larvae will bite the tool defensively, allowing the birds to retreat and eat it. But crows have to put down their tools while eating, so they can fall to the ground or even be robbed.
The researchers used 27 wild-caught crows for their experimental trials so that their results were not biased by previous training.
Giving crows a choice between the two types of tools, the team confirmed that birds strongly prefer to use tools with hooked sticks.
Non (left) and hook (right) tools and their use. (James St Clair et al, Nat. Ecol. Evol, 2018)
“Hanging tools are not only more expensive to obtain, but they are also much more effective,” said Christian Rutz, behavioral ecologist at the University of St Andrews.
“Depending on the foraging task, crows can extract their prey with these tools up to 10 times faster than with standard non-hooked bog tools.”
Seventeen of the birds were then observed in two trials each on different days. In both, they were presented with logs containing holes of different sizes baited with meat or spiders. In one treatment they had access to branches suitable for constructing hook tools and the other with only straight sticks.
“Subjects were much more likely to express conservation behavior (storing tools underfoot or in holes) when rummaging with hooked-stick tools they had made … paper.
This held true when the hanging tools were provided by the researchers, suggesting that the tool itself was given an assigned value rather than the time they spent on it.
Plus, they used the safest method of preservation – storing tools in holes – much more for tools with hooks.
“It was exciting to see that the crows are just a little more careful with more efficient and more expensive tools to replace,” said James St Clair, ethologist at the University of St Andrews.
“This suggests that they have some conception of the relative ‘worth’ of different types of tools.”
Since corvids, including crows and New Caledonian crows, have also shown their ability to plan ahead, it makes sense that they could also assign a value to the objects they use to prioritize them. .
The team notes that not all New Caledonian crows make the tools with hooked sticks, so their findings can only be generalized to those populations that do. Their sample size was also too small to fully disentangle some of the variables, like choice of material, they concede.
But at least one other species of raven, the Hawaiian crow (Corvus hawaiiensis) has also demonstrated such conservation behavior.
We have long underestimated the capabilities of birds given their relatively small brains. But physiological studies have shown that the dense packaging of their neurons compensates for their lack of size.
Behavioral studies continually reveal that these modern dinosaurs are capable of behaviors that we once thought humans were capable of – such as self-control – proving, like all the rest of biology, that intelligence is a complicated and messy spectrum that did not appear spontaneously with the arrival of our species.
This research was published in eLife.
