Both songbirds and humpback whales organize their communication using the same statistical principles that underlie every human language on Earth. This is the conclusion reached by researchers from an international team who conducted two interrelated studies.
These same researchers previously published their findings on humpback whale song in the journal Science. Taken together, these studies suggest that some of the deepest mathematical regularities in human language are not unique to humans. They arise wherever complex communication is learned and passed down from generation to generation.
Both studies revealed a pattern consistent with Zipf's law. Linguists have documented both patterns in all human languages and cultures. Both are now found in the songs of Bengalese finches and humpback whales. Some song fragments are used constantly, while most are used only occasionally. Furthermore, frequently used fragments tend to be shorter, while rarely used fragments tend to be longer. This particular variation is known as Zipf's law of contraction.
The same structure is observed in birdsong.
Researchers analyzed the songs of Bengalese finches, renowned for the complexity of their learned melodies, and discovered statistically consistent note sequences that functioned like words. Some sequences occurred repeatedly and frequently. Most appeared only occasionally. The distribution matched the Zipfian pattern observed in human vocabulary.
The research team used methods borrowed from studies of how infants recognize words in speech. Infants track which sounds frequently occur together to determine where one word ends and the next begins. The same method, applied to birdsong, revealed the same hidden structure.
Data collected at various stages of development showed that these patterns were present even in the earliest attempts at song, even before adult songs had developed. Apparently, the structure emerges through the learning process itself, rather than from any memorized template.
The same structure is present in whale songs.
The results of the bird song study directly complement the team's earlier work on humpback whales. In that study, published in the journal Science, the researchers found that humpback whale songs also obey Zipf's law and Zipf's law of contraction. Frequently used vocal sequences were shorter than rarely used ones, and the frequency distribution of sequences matched the pattern found in human language.
Humpback whale songs are transmitted culturally. Individual whales learn to sing by listening to other individuals in their population, and the songs change over time as new elements emerge and spread. Researchers argue that it is this learning process that creates the statistical structure. He called the discovery of this property, shared by both whale and bird songs, a pleasant surprise.
Professor Kazuo Okanoya of Teikyo University, who has studied the song of Bengalese finches for many years, said: "Frequently used syllable fragments tend to be shorter, while less frequently used fragments tend to be longer - this pattern is known as Zipf's law.".
Culture as a common thread
The key connection between humans, whales, and songbirds lies not in shared ancestry, but in shared learning. All three species acquire their communication systems by listening to others and passing on this knowledge to the next generation. They do not inherit their songs or languages through genes. This process of cultural transmission, the researchers argue, is the reason for the emergence of statistical patterns. When a complex communication system is learned and passed down from generation to generation, Zipf's structure becomes a natural consequence.
Humans and songbirds are separated by more than 300 million years of evolution. Professor Simon Kirby of the University of Edinburgh called this similarity astonishing. Professor Inbal Arnon of the Hebrew University of Jerusalem said these results do not diminish the uniqueness of language. But they suggest that its most fundamental properties may be present wherever communication is passed down through generations within a culture. This is true for species as diverse as humpback whales, songbirds, and human children.
The results of the study were published in the journal Science Advances .