Researchers have discovered that wild Yellow-naped Amazon parrots employ syntax – a set of rules governing the arrangement of sounds – when communicating through complex vocalizations known as “warble duets.” The findings, published in the issue of the Journal of Avian Biology, challenge the long-held assumption that complex language structures are unique to humans.
Christine Dahlin, a professor of biology at the University of Pittsburgh at Johnstown, led the research team. Her work builds on previous studies demonstrating simpler “standard duets” – consisting of fewer distinct calls – also exhibit syntactic rules. The question was whether the more elaborate warble duets, characterized by a significantly larger repertoire of sounds, would adhere to similar organizational principles or represent a more chaotic form of communication.
“Ultimately I really want to understand how these birds are communicating in the wild,” Dahlin said. “I want to know what they are saying, and how they are saying it.”
The study focused on Yellow-naped Amazon parrots (Amazona auropalliata), a critically endangered species inhabiting regions from southern Mexico to southern Costa Rica. The parrots’ complex vocalizations are particularly prominent during territorial disputes, suggesting a link between communicative sophistication and social dynamics. Dahlin and her team spent three years recording parrot duets at breeding sites in Costa Rica, utilizing directional microphones to capture high-quality audio data. The final analysis comprised approximately 50 warble duets from 13 mated pairs, totaling over 450 individual calls, each lasting between five and ten seconds.
The researchers identified 36 distinct call types within the warble duets, along with additional variations. This represents a substantial increase in lexical diversity compared to the four call types observed in the simpler standard duets. The distribution of these calls wasn’t random; the team found that males and females tended to produce certain sounds more frequently than others, demonstrating a degree of vocal specialization.
A key observation was the consistent pattern of call alternation within the duets. Typically, the female initiates the sequence, followed by a response from the male, indicating a precise level of coordination. The team achieved a 92% agreement rate in classifying these calls, bolstering the reliability of their analysis.
To uncover the underlying syntactic structure, the researchers employed Voyant Tools, a software package commonly used for analyzing textual data. This allowed them to identify “collocates” – pairings of calls that occurred more frequently than expected by chance – and “negative collocates” – calls that never appeared together. The analysis revealed 19 positive collocates and four negative collocates, demonstrating a non-random organization of vocal elements.
The findings indicate that the parrots’ warble duets are governed by a set of rules dictating how sounds are combined. Approximately half of the identified call types were found to occupy specific positions within the duet sequence – beginning, middle, or end – further supporting the presence of a structured system. Despite these rules, the duets exhibited considerable flexibility; only two of the 54 analyzed duets followed identical sequences, while the remainder represented unique combinations adhering to the established combinatorial rules.
“These duets are marked by a wide lexicon of 36 call types, with additional variants,” the researchers noted. “We found more than 20 syntactic rules (positive and negative collocates), flexibility in when calls are presented throughout the duets, varying degrees of sex bias, and a large repertoire of 36 call types.”
It’s important to note that while the study established the presence of syntax, it did not demonstrate a corresponding semantic system – a mapping between calls or call combinations and specific meanings. The observed structure relates to the order and arrangement of vocal elements, not necessarily to their conceptual content. The concepts of pragmatics – how context influences meaning – also remain unexplored in this research.
The discovery strengthens the hypothesis that combinatorial syntax can emerge in animals with complex social lives. The application of linguistic tools to animal communication provides a novel framework for comparing and analyzing communication systems across species. This approach also has implications for conservation efforts, as it highlights the importance of preserving not only parrot populations but also the intricate vocal traditions that underpin their social interactions.
The Yellow-naped Amazon parrot faces threats from habitat loss and illegal capture, jeopardizing both the species’ survival and the transmission of its unique vocal culture. Protecting these parrots means safeguarding a complex network of interaction and vocal learning, representing a singular biological heritage.
