By Chelsea Whyte
New Caledonian crows are really smart. They are known for their toolmaking abilities, such as bending sticks into hooks to skewer grubs for dinner or to carry objects. Now we’ve seen they have impressive planning skills too.
Romana Gruber at the University of Auckland in New Zealand and her colleagues set up a series of compartments that held different sized sticks or stones, which had to be retrieved in a certain order to ultimately get to a piece of meat. Each apparatus was separated from the others with a wooden divider, so the crows could only see one at a time.
The team let the crows learn where the different compartments were before putting them to the test in three slightly different setups. For example, in one test, they had to take a stick from one compartment and use it to pull a stone from a tube, and then take that stone to a platform where it would release food. During the test, the crows had to ignore a compartment that held a second stick, which was designed to distract them from getting the stone.
The team had 11 wild New Caledonian crows take this test – after 20 trials, four crows were successful 80 per cent of the time, and the rest of the birds took 40 trials or more to reach that success rate.
When the team swapped the tools, putting the stone as the first step, it took all the crows more than 40 trials to get the sequence right. This may be because tool use takes up cognitive power, Gruber says, and while crows naturally use sticks as tools, they don’t do the same with stones.
The experiment may not be able to rule out whether the birds are learning during the trials rather than planning, says Sarah Jelbert at the University of Cambridge. “But each time they’re seeing the puzzle, they need to work out what are the steps to get to the end and then plan how to take them,” she says.
It’s a bit like a game of chess – you may be familiar with the pieces and the board, but you still have to plan a strategy a few moves ahead. “The animals have to know the rules here, where is that second tool, where is the piece of food,” she says. Performing several steps while they can’t see the entire puzzle shows that they can hold the space in their memory think through how to interact with it.
“I think they’re planning, of course. But most of them don’t solve this immediately,” says Mathias Osvath at Lund University in Sweden. “It would have been very strange if they couldn’t do this, given earlier experiments showing their tool use and the ability corvids have to plan.”
Osvath says that ravens also show that they can plan ahead while using tools, which is impressive because they aren’t natural tool-users like crows. But this has been shown only for one task, not a sequence of steps.
Journal reference: Current Biology, DOI: 10.1016.j.cub.2019.01.008
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