Two bird species, the Barbados bullfinch and the Carib grackle, have passed the string-pulling test, joining an elite group of animals capable of completing one of the most challenging animal cognition tests.
The goal of the research, which was led by Jean-Nicolas Audet, a Ph.D. candidate in the Department of Biology at McGill University in Canada, is to determine the origin of innovative behavior in birds. Throughout the study, which was published Wednesday in the journal PLOS One, two of the 31 grackles and 18 of the 42 bullfinches were able to complete the string-pulling task, but what was surprising about their finding was lack of correlation between this and other cognitive tasks.
"Most people previously assumed that string-pulling was just a problem-solving task and that the performance on both should be correlated. Some people even think that performance on all behavioral tasks should be correlated to some extent," Mr. Audet tells The Christian Science Monitor in an email. "Our study challenges those views.”
The two species were chosen for the study for their innovative use of problem solving in the wild – the bullfinch even steals and opens sugar packets.
The birds used in the study were captured from the wild, rather than being bred in captivity, which creates additional variables that may have influenced the bird’s ability to complete the tasks – although growing up around humans could also facilitate the task. However, Audet says, using wild birds better exhibits skills required in the bird's natural habitat and provides a more representative sample of the population.
Food was placed in a container and suspended at the end of a string, requiring the birds to complete a complex series of movements, including repeatedly pulling with their beaks and holding loops in the string with their feet to get at the food. Ability to complete the task shows a high level of cognitive ability, because the birds must repeat the movement multiple times over before being rewarded.
Birds that were given a second chance at the task showed improvement, suggesting that motor trial-and-error learning may have occurred and that these types of skills are not spontaneous, but developed.
String-pulling tests have been used in animal cognition studies before, but no other research has compared the results to those from other cognition tests, as Audet's team did – although the grackles' data was disqualified from correlational analysis, since they had not performed well enough on the string-pull test to be useful.
Audet and his team had each bullfinch perform tests in six other cognitive categories, including shyness, neophobia, problem-solving, discrimination, and reversal learning performance. However, they found that ability to pull the string did not correlate with any of the other tasks.
"We certainly did not expect that the string-pulling scores would not correlate with scores on other tasks, especially with problem-solving tasks, mainly because we presumed that string-pulling was just another a problem-solving task," Audet tells the Monitor in an email. "It is possible that the type of problem that needs to be solved is requiring specific cognitive abilities.... Some birds are good at one while others are good at the other task – a variation that can be seen even within the same species."
In that way, Audet says, birds are like humans: some people are good at solving mechanical problems like fixing cars, while others' forte is more abstract logic, helping them excel at games like chess.
Ed Wasserman, a professor of psychology at the University of Iowa who has done similar comparative cognition research, saw another potential difference that would affect the outcome of string test research: not within species, but between them. Not all animals have the same motor skills, and yet variations of the string pull test have been used with dozens of different animals.
He addressed this problem in his own research by designing a computerized string pull task in which animals can simulate the task of pulling on a string with a touch screen, taking the motor skills variable out a test that is ultimately about cognitive skills, not physical ability.
Not all birds have the motor skills to lift the bucket, or grasp the string, but that doesn't mean they couldn't learn them, Wasserman tells the Monitor. However, "the touch screen will give us a route to uniformity, some way that we might more systematically make regular the nature of the task so that the motor differences and perceptual differences of the species might be more effectively controlled," he says.
Both Audet and Wasserman expect that these most recent findings will inform further research into animal behavior and cognition.
"We are in the midst of a really exciting period in the realm of comparative cognition," Wasserman tells the Monitor. "The public has never been more interested, and the methods have never been more powerful. The better we get, the more we can inform the public about how smart animals really are, because limits on animal intelligence are largely our limits.… Darwin suggested that we could learn a great deal about ourselves by studying our relatives. Well, they are all around us."