There are lots of animals, including dogs and apes, that can communicate in something we might understand as sentences. But only one non-human species has complex enough communication that they actually need grammatical rules. Say hello to the Bengal finch.
What we're specifically talking about here is syntax, the idea that individual units of meaning need to be arranged in a certain way for the sentence as a whole to make sense. Syntax is why "man bites dog" means something completely different from "dog bites man" to an English speaker, and it's why "bites man dog" or dog man bites" are just gibberish. Kyoto University researcher Kentaro Abe has now been able to demonstrate that Bengal finches demonstrate similar syntactical awareness.
These birds are known to react vehemently whenever they hear an unfamiliar bird call, replying with a flurry of calls. Abe played recordings of these calls to a bunch of finches until they became familiar enough with the calls to remain calm when they heard them. He then took the records and edited them so that the individual syllables of the calls were all jumbled up. Abe and his team created four remixes, which they then again played to the birds.
The birds only reacted to one of the four jumbled versions, which means that they now considered this particular remix to be something fundamentally different from the original call or the other remixes. Abe believes that the other three jumbled versions still satisfied the rules of finch grammar, and so they didn't provoke a reaction. But the fourth version sounded wrong to the finches, which is why they reacted as though they had never heard anything like it before.
In followup studies, the researchers demonstrated that this finch grammar needs to be learned from interaction with a larger community, as birds raised in isolation were unable to pick up on why the remix was wrong. He also used the remixes to teach birds an artificial grammar of call sounds, and then played new remixes that violated these newly created rules. Finally, he chemically destroyed a part of the brain known as the anterior nidopallium, which allows finches to recognize faulty grammar in much the same way our own Broca's area allows humans to pick up on errors.
Constance Scharff of Berlin's Free University explains the significance of Abe's research:
"It's an ingenious experiment showing that birds are sensitive to changes in song that are consistent with different grammars. More and more, we are seeing similarities between humans and animals, and that makes some people uneasy."
Abe is hopeful that further study into the anterior nidopallium will help reveal just why finches and humans alike evolved a capacity for grammar.