First evidence that birds tweet using grammar
- 18:00 26 June 2011 by Andy Coghlan
They may not have verbs, nouns or past participles, but birds challenge the notion that humans alone have evolved grammatical rules.
Bengal finches have their own versions of such rules – known as syntax – says Kentaro Abe of Kyoto University, Japan. "Songbirds have a spontaneous ability to process syntactic structures in their songs," he says.
To show a sense of syntax in the animals, Abe’s team played jumbled "ungrammatical" remixes of finch songs to the birds and measured the response calls.
Although many animals, including dogs, parrots and apes are known to interpret and construct "sentences", and recognise human words for individual objects, Abe says that only his finches have been shown to have a form of grammar in their utterances. Similar claims have been made for whale song, however.
In the wild, Bengal finches call back vigorously whenever they hear unfamiliar songs, usually from intruding finches. In the lab, Abe and colleague Dai Watanabe of the Japan Science and Technology Agency in Saitama exploited these reactions to gauge whether finches could notice "ungrammatical" songs.
First, they played finches unfamiliar songs repeatedly until the birds got used to them and stopped overreacting. Then they jumbled up syllables within each song and replayed these versions to the birds.
"What we found was unexpected," says Abe. The birds reacted to only one of the four jumbled versions, called SEQ2, as if they noticed it violated some rule of grammar, whereas the other three remixes didn’t. Almost 90 per cent of the birds tested responded in this way. "This indicates the existence of a specific rule in the sequential orderings of syllables in their songs, shared within the social community," Abe told New Scientist.
In subsequent experiments Abe showed that the rules were not innate – they had to be learned. Birds raised in isolation failed to react to SEQ2 until they had spent two weeks with other birds. He also taught birds unnatural grammatical rules by habituating them to one of his jumbled versions, then gauging their reactions to remixed versions that violated the "artificial" rules.
Finally, Abe chemically destroyed an area of the brain called the anterior nidopallium in some birds, and was thereby able to demonstrate that it is vital for registering faulty grammar. In humans, a region called Broca’s area is activated when we hear ungrammatical sentences, so Abe suggests that studying the counterpart region in finches might throw new light on the origins of human grammar.
Constance Scharff, who works on birdsong at the Free University of Berlin, Germany, says the work is important because it is often claimed that humans are the only species that uses grammar.
"It’s an ingenious experiment showing that birds are sensitive to changes in song that are consistent with different grammars," she says. "More and more, we are seeing similarities between humans and animals, and that makes some people uneasy."
Journal reference: Nature Neuroscience, DOI: 10.1038/nn.2869