The song of a bird learned from its fellow birds may end up displaying statistical regularities familiar to linguists.
A study published in Science Advances shows that certain structures observed in human language also appear in learned bird song. This finding reinforces a specific idea: cultural transmission alone can favor certain forms of signal organization.
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The comparison does not mean that birds possess a language comparable to ours. Here, the researchers are interested in the frequency and ordering of sound units, not their meaning. In other words, two very different systems can share mathematical properties without conveying the same type of information.
One of these properties concerns the way certain units recur much more often than others. In human languages, this highly uneven distribution is well known. A few words are ubiquitous, then their frequency drops rapidly as one moves down the ranking. Recent work has found a related organization in the song of humpback whales.
The new study specifically sought to determine whether a comparable phenomenon could appear in birds whose song is learned. This is an important point, because young songbirds do not simply produce a sequence that is entirely programmed at birth. They listen to adults, memorize models, and then gradually adjust their own vocalizations.
This transmission provides a natural laboratory for studying the effect of learning on the shape of a communication system. When a sequence must be memorized and then reproduced, some organizations may be retained more easily than others. Over successive learning episodes, regularities that are transmitted well may therefore become more frequent.
Concretely, the authors looked for distributions in songs comparable to those already measured in human language and in whales. Their analysis shows that such structures do emerge in the learned signal. The result thus aligns with the work on humpback whales, despite the great evolutionary distance separating birds, cetaceans, and humans.
This statistical resemblance, however, does not allow us to speak of words or grammar in the human sense. A song can be strongly structured without encoding sentences composed of distinct meanings. The comparison therefore concerns the organization of the signal and its transmission, not the mental content associated with each sound.
The result is of particular interest for the study of cultural evolution. If analogous properties appear in several animal lineages where vocalizations are learned socially, they could be a general consequence of repeated transmission. This hypothesis can now be tested in other species that learn their signals, and then compared with species whose vocalizations are mainly innate.
The next step is precisely to determine how far this rule generalizes. Researchers can now look for the same statistical signatures in different learned vocal systems and check whether they disappear when cultural transmission plays a much weaker role.