Humans aren't alone in being able to grasp early grammatical concepts, say biologists who found songbirds can as well.

European starlings were trained to tell the difference between a regular "sentence" of birdsong and one with a clause embedded in it.

The findings by psychologist Timothy Gentner of the University of California at San Diego challenge a finding by linguist Noam Chomsky.

Chomsky theorized humans are unique in the animal world in their ability to use recursive grammar – that is, inserting an explanatory clause such as this one – in sentences.

Gentner's team showed starlings could recognize a recursive type of grammar involving warbles and rattles instead of words.

Of the 11 songbirds tested, nine were able to pick out the inserted phrases about 90 per cent of the time, the team reports in Thursday's issue of the journal Nature.

Starlings show grasp of grammar

Similar experiments on tamarin monkeys showed the primates could not recognize recursive grammar.

"An intriguing possibility is that the capacity to recognize recursion might be found only in species that can acquire new patterns of vocalization, for example, songbirds, humans and perhaps some cetaceans," psychologist Gary Marcus of the University of New York wrote in a journal commentary accompanying the study.

Marc Hauser, director of Harvard University's Cognitive Evolution Laboratory, conducted the experiments on tamarin monkeys.

Gentner's findings don't disprove Chomsky's idea because the starlings are showing a grasp of basic grammar but not the semantic ability to generalize from patterns, Hauser told the Associated Press.

Gentner is planning more experiments to test if the starlings can generalize.