Recursion, language, and starlings

It has been claimed that recursion is one of the properties that distinguishes human language from any other form of animal communication. Contrary to this claim, a recent study purports to demonstrate center-embedded recursion in starlings. I show that the performance of the birds in this study can be explained by a counting strategy, without any appreciation of center-embedding. To demonstrate that birds understand center-embedding of sequences of the form A(n) B(n) (such as A(1) A(2) B(2) B(1) , or A(3) A(4) A(5) B(5) B(4) B(3) ) would require not only that they discriminate such patterns from other patterns, but that they appreciate that elements must be bound from the outside in (thus, in the above examples, A(1) B(1) , A(2) B(2) , A(3) B(3) , A(4) B(4) , A(5) B(5) are bound pairs). This has not been shown in nonhuman species, and sentences with this structure are difficult even for humans to parse. There appears to be no evidence to date that nonhuman species understand recursion.