The research, published in the journal Science Advances, focused on two species of bird from Barbados with very different personalities.

Barbados bullfinches are bold, opportunistic and innovative while black-faced grassquits are shy and conservative.

In laboratory tests, the birds differed widely in their ability to solve problems. While most of the bullfinches quickly worked out how to lift the lid of a jar of food, all of the grassquits were stumped by the challenge.

A comparison of gene activity in the birds' brains - especially the part corresponding to the human pre-frontal cortex - revealed one striking difference.

Levels of a neurotransmitter receptor associated with intelligence in humans were higher in the bullfinches.

The protein, known as GRIN2B, plays a key role in the transmission of particular nerve signals across synapses, the brain wiring "junctions" that connect neurons.

When GRIN2B is boosted in genetically engineered mice, the animals become better learners.

Lead researcher Jean-Nicolas Audet, from McGill University in Canada, said: "By comparing an extremely innovative species like the Barbados bullfinch with a closely related conservative one like the black-faced grassquit, we gain insight into the evolutionary mechanisms that can lead to divergence in behaviour.

"It might be that mammals, including humans, and birds like the Barbados bullfinch use similar mechanisms to perform cognitively.

"If our results are confirmed in future studies, it would be a unique demonstration of convergent evolution of intelligence, involving the same neurotransmitter receptors despite the widely different brain structures of birds and mammals."

Australian Associated Press