The finding is remarkable because the crows received no assistance or training at all.Clever crows have shown how they can assemble tools from two or more non-functional components, a feat previously only seen in humans and great apes.
Scientists videoed captive Caledonian crows slotting together rod pieces to create a tool long enough to extract a food reward.
In one experiment, the birds were presented with the barrels and plungers of disassembled syringes.
Without any help or demonstration, four of the eight birds partially inserted the plunger to manufacture the right length of tool.
One star performer, called Mango, was able to make compound tools out of three and even four parts.
The birds used the tools to drag a piece of food, a grub, along a slot to an open doorway.
Researcher Dr Auguste von Bayern, from Oxford University and the Max-Planck Institute for Ornithology in Germany, said: “The finding is remarkable because the crows received no assistance or training in making these combinations, they figured it out by themselves.”
New Caledonian crows (Corvus moneduloides), from the island chain of New Caledonia in the South Pacific, are renowned for their tool-making ability.
In 2002, a New Caledonian crow called Betty famously became the first animal shown to be able to create a hooked tool by bending pliable material.
Professor Alex Kacelnik, from Oxford University, said: “The results corroborate that these crows possess highly flexible abilities that allow them to solve novel problems rapidly, but do not show how they do it.
“It is possible that they use some form of virtual simulation of the problem, as if different potential actions were played in their brains until they figure out a viable solution, and then do it.
“Similar processes are being modelled on artificial intelligences and implemented in physical robots, as a way to better understand the animals and to discover ways to build machines able to reach autonomous creative solutions to novel problems.”
The research is published in the journal Scientific Reports.