Great tits use different alarm calls for different predators, according to a scientist in Japan.
The researcher analysed the birds' calls and found they made "jar" sounds for snakes and "chicka" sounds for crows and martens.
This, he says, is the first demonstration birds can communicate vocally about the type of predator threatening them.
The findings are published in the journal Animal Behaviour.
From his previous observations, the researcher, Dr Toshitaka Suzuki, from the Graduate University for Advanced Studies in Kanagawa, found great tits appeared to be able to discriminate between different predators.
To test whether they could also communicate this information, he placed models of three different animals that prey on nestlings - snakes, crows and martens - close to the birds' nest boxes.
He then recorded and analysed the birds' responses.
"Parents usually make alarm calls when they approach and mob the nest predators," said Dr Suzuki.
"They produced specific 'jar' alarm calls for the snakes and the same 'chicka' alarm call in response to both the crows and martens," he said.
But a closers analysis of the sounds showed the birds had used different "note combinations" in their crow alarm calls from those they had used for the martens.
Dr Suzuki thinks the birds might have evolved what he called a "combinatorial communication system" - combining different notes to produce calls with different meanings.
Since snakes are able to slither into nest boxes, they pose a much greater threat to great tit nestlings than other birds or mammals, so Dr Suzuki says it makes sense that the birds would have a specific snake alarm call.
He added: "Human language is based on a combinatorial rule, which allows us to generate an infinite number of expressions (ie words) from a finite set of elements (ie alphabets). Similarly, the tits can make a word 'crow' or 'marten' by combining different types of notes into an alarm call."