Crows have the brain power to solve higher-order, relational-matching tasks, like humans, apes and monkeys, a new study has found.
Crows have long been heralded for their high intelligence - they can remember faces, use tools, and communicate in sophisticated ways.
The new study has found crows also have the brain power to solve higher-order, relational-matching tasks, and they can do so spontaneously.
That means crows join humans, apes, and monkeys in exhibiting advanced relational thinking, according to the research.
"What the crows have done is a phenomenal feat," said Ed Wasserman, a psychology professor at the University of Iowa and corresponding author of the study.
"That's the marvel of the results. It's been done before with apes and monkeys, but now we're dealing with a bird; but not just any bird, a bird with a brain as special to birds as the brain of an ape is special to mammals," said Wasserman.
The study involved two hooded crows that were at least 2 years old. First, the birds were trained and tested to identify items by colour, shape, and number of single samples.
The birds were placed into a wire mesh cage into which a plastic tray containing three small cups was occasionally inserted. The sample cup in the middle was covered with a small card on which was pictured a colour, shape or number of items.
The other two cups were also covered with cards - one that matched the sample and one that did not.
During this initial training period, the cup with the matching card contained two meal-worms; the crows were rewarded with these food items when they chose the matching card, but they received no food when they chose the other card.
Once the crows have been trained on identity matching-to-sample, the researchers moved to the second phase of the experiment.
This time, the birds were assessed with relational matching pairs of items. These relational matching trials were arranged in such a way that neither test pairs precisely matched the sample pair, thereby eliminating control by physical identity.
"Analogical reasoning, matching relations to relations, has been considered to be among the more so-called 'higher order' abstract reasoning processes," said Anthony Wright, neurobiology and anatomy professor at the University of Texas-Houston Medical School.
"For decades such reasoning has been thought to be limited to humans and some great apes. The apparent spontaneity of this finding makes it all the more remarkable," he said.
The research was published in the journal Current Biology.
