Some birds understand syntax

Syntax has long been considered unique to human language, and language in turn is often thought to set humans apart from other animals. Yet Suzuki found it not in a bird typically celebrated for intelligence, like crows or parrots, but in humble P. minor.

The Nature paper linked in the NatGeo article is fascinating :

Here we find that Japanese great tits extract different meanings from ABC and D calls, and a compound meaning from ABC–D calls. As tits fail to produce a compound response when the note sequence is artificially reversed (D–ABC), these findings support the hypothesis that the communication system of tits represents semantically compositional syntax.

And back to NatGeo :

Once he realized that birds are using their own form of language, Suzuki wondered: what happens in their minds when they talk? Might words evoke corresponding images, as happens for us?

Suzuki tested that proposition by broadcasting recordings of P. minor’s snake-specific alarm call from a tree-mounted speaker. Then he analyzed the birds’ responses to a stick that he’d hung along the trunk and could manipulate to mimic a climbing snake.

If the call elicited a mental image, Suzuki figured the birds would pay extra-close attention to the snake-like stick. Indeed they did, he recently reported in the journal Proceedings of the National Academy of Sciences. In contrast, when Suzuki broadcast a call used by tits to convey a general, non-specific alarm, the birds didn’t pay much notice to the stick. And when he set the stick swinging from side to side in a decidedly non-snakelike manner, the birds ignored it.
https://news.nationalgeographic.com/2018/02/japanese-songbirds-process-language-syntax/