Birds may follow a hidden pattern of human language

Birds may seem to be singing randomly, but new research suggests their vocalizations may follow hidden rules similar to those that govern human language.

Over the past three decades, scientists have used birdsong as models to understand how humans acquire and transmit language. 

Birdsong even serves as a tool for studying speech disorders in humans because it shares biological similarities with human speech. Unlike human subjects, birds can be studied in natural conditions without significant ethical or logistical barriers. 

Birds sing through notes and calls

But do birds follow the same linguistic rules as we do? To explore this question, it helps to first understand how birds structure their songs.

Notes are continuous sounds separated by short pauses, while phrases are short sequences of notes that always appear together.

Calls are typically short, innate sounds, whereas songs are longer sequences of learned notes or phrases. Bouts are series of similar calls or songs separated by longer rests.

But do these patterns reflect true linguistic rules? One of the best candidates is Zipf’s law of abbreviation (ZLA), a principle that shows up in nearly every human language.

ZLA predicts that frequently used words or sounds tend to be shorter, while rare ones are longer. A team of researchers, including Rebecca Lewis of the University of Manchester, set out to put ZLA to the test.

Human language pattern in bird songs

The researchers developed a new method to test ZLA. They introduced an R package called ZLAvian and analyzed songs from 11 populations across seven species archived in the Bird-DB.

Overall, the results showed a weak but consistent tendency to use shorter sounds more frequently. However, at the individual population level, only one out of eleven showed strong evidence of ZLA.

Studying ZLA in birdsong presented several challenges that are absent in human language. Most bird populations use only a few note types compared to our many words, making it difficult to see clear links between sound length and frequency.

Because birds copy songs from others rather than creating them, any variations could reflect shared learning rather than something that emerged independently.

Mixed results in different bird species

More than three decades ago, Jack P. Hailman and colleagues noticed that black-capped chickadees often produced shorter bouts of calls frequently than longer ones, but the pattern did not clearly match Zipf’s Law.

Later studies showed mixed results. A 2013 study found no evidence of ZLA in common ravens, while a 2020 study of captive African penguins suggested shorter notes were more common.

More recently, some researchers found no evidence of ZLA in the calls of domesticated Java sparrows, while others reported evidence in wild house finches.

The bigger question of language

The challenges lead to the bigger question. Do birds really follow ZLA, or should we even expect them to? In humans, it is one of the most consistent patterns in language.

The idea of ZLA comes from the Law of Least Effort, which suggests that people naturally choose the path of least resistance to achieve a goal. 

Interestingly, ZLA is not only applicable to spoken words but also to written symbols and texts. However, when it comes to animals – including primates, cetaceans, bats, and even hyraxes – the evidence is unclear. Very few studies have tested whether ZLA holds true for birds.

Bird talk can’t be simplified

For humans, shortening words rarely changes their meaning – “television” and “TV” both convey the same idea. But in birdsong, the exact sound of a note can carry crucial information.

In some species, females interpret particular notes as signals of male quality, and because these notes may be difficult to produce, even slight alterations could distort the message and affect mate choice. This sensitivity might explain why the linguistic principle of Zipf’s Law of Abbreviation (ZLA) is not consistently observed in birdsong.

While the study found some hints of the pattern in certain species and populations, others showed no evidence at all, suggesting that if ZLA exists in birdsong, it is far less consistent than in human language.

Future research with larger datasets and broader sampling will be essential to determine whether this linguistic rule truly applies to birds when they communicate.

The full study was published in the journal PLOS Computational Biology.

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