THE humble Australian magpie is the star of new research that suggests social interaction is key to the development and evolution of intelligence in animals.
And when it comes to developing smarts, it seems the more birds in the group, the merrier.
In a study published by the journal Nature on Wednesday, researchers from the University of Western Australia and the University of Exeter, UK, found magpies living in larger groups appeared to be smarter than those in smaller groups.
The study also found clever female birds made better mothers, with a higher success rate when it came to both hatching their eggs and raising their young.
Study co-author Dr Benjamin Ashton said it backed up "the social intelligence hypothesis", a theory that posits intelligence in animals evolved in response to the demands of living in complex social systems. Previously, this theory had only been tested by comparing the brain size of different animal species, usually in captivity.
"The link between brain size and intelligence is slightly contentious in itself," he said. "But also the majority of studies that have looked at the relationship between cognition and sociality have done the studies in captive conditions, where the selective pressures are arguably quite different to those in the natural environment. We were able to do it on a wild population of Australian magpies which is quite unique as well."
In work that began in 2013, researchers studied the behaviour of 56 wild magpies, individually tagged, living in 14 territorial groups of between three and 12 birds in the Perth suburb of Guildford.
Magpies were chosen for the task because of their territorial nature, which means the same group of birds will always be found in the same place. They're also relatively comfortable with humans, despite being wild.
The birds' cognitive ability was tested using a number of activities. One task, which tested spatial awareness, involved repeatedly giving the birds a foraging board in which their food reward was hidden, always in the same place. Birds that lived in bigger groups would more quickly learn to look in the right place for their food.
Having established the cognitive ability of individual adult birds, the researchers were then able to look at the effect of a mother-bird's intelligence on her reproductive success. They found smarter female birds hatched more eggs, and successfully raised more young - but the reason why is yet to be worked out, Dr Ashton said.
As for the fledgling birds, cognitive tests indicated their intelligence also developed socially. They were tested at 100, 200 and 300 days old. At 100 days, there was little difference between the birds in big groups and small groups. At 200 and 300 days, it became clear the birds in the larger groups were getting smarter.
This finding brings up the age-old question of nature versus nurture. The social intelligence hypothesis has traditionally viewed intelligence as genetically determined, Dr Ashton said, "but we have shown here that the social environment has an effect on cognitive development.
"What we need to determine now is whether selection can act upon the cognitive changes that the social environment has caused."
