US: Humans may no longer be the unique linguists we think we are - the common starling has proved it can learn equally complex language patterns, research revealed yesterday.
The songbirds have shown they can understand a linguistic sequence known as recursive centre-embedded grammars.
In humans, this means a person can include an infinite amount of grammatical utterances into a sentence. Sentences such as "Oedipus ruled Thebes", can be extended to read "Oedipus, who killed his father, ruled Thebes" or "Oedipus, who killed his father, whom he met on the road from Delphi, ruled Thebes" and so on.
Linguists have long believed only humans could do this.
But scientists found that the European starling, renowned as an expert mimic, can learn such patterns.
Timothy Gentner, assistant professor of psychology at the University of California, San Diego, said: "Our research is a refutation of the canonical position that what makes human language unique is a singular ability to comprehend these kinds of patterns.
"If birds can learn these patterning rules, then their use does not explain the uniqueness of human language."
Prof Gentner and his team created artificial starling songs that followed two patterns. One adopted recursive centre embedding known as "context free" and the other using "finite state", which means sounds can only be added at the beginning or the end.
Eight starling songs followed the context-free pattern, while eight followed the finite state.
Scientists then taught 11 adult starlings to distinguish between the two patterns, rewarding them with food when they pecked at a button on hearing the context-free songs, but desisting when listening to the finite state songs.
After between 10,000 and 50,000 trials over several months carried out at the University of Chicago, nine of the starlings learnt to differentiate between the two.
The birds were then played different examples of the two patterns and the starlings "performed well above chance".
The scientists found that the starlings could distinguish between the two patterns, even when the songs were increased to longer sequences.
Prof Gentner said the finding that starlings can grasp these simple grammatical rules suggests humans and other animals share basic levels of pattern recognition.
"There might be no single property or processing capacity that marks the many ways in which the complexity and detail of human language differs from non-human communication systems," he said.
"Fifty years ago, it was taboo to even talk about animal cognition. Now... no one doubts that animals have complex and vibrant mental lives.
"This study is a powerful statement about what even birds can do - look at what they're learning."
Prof Gentner said he was considering working with juvenile starlings to see if they were more adept at learning syntax patterns than adults.