Yellow-naped Amazon Parrots Use Complex Warble Duets

Have you ever listened to a parrot speak and wondered whether birds possess a language of their own? Videos online show parrots imitating human voices, singing tunes and even reproducing the sounds of a noisy city.

Yet what occurs in the wild, away from cages and cameras? When parrots communicate with one another, do they follow established rules?

Professor Christine R. Dahlin of the University of Pittsburgh at Johnstown set out to investigate this question. Her team examined how yellow-naped Amazon parrots communicate during fierce territorial disputes.

“Ultimately I really want to understand how these birds are communicating in the wild,” she said. “I want to know what they are saying, and how they are saying it.”

Yellow-naped Amazon parrots and social complexity

Yellow-naped Amazon parrots range from southern Mexico to southern Costa Rica, and the species is critically endangered. Their social lives are highly complex.

Large flocks roost together at night, before splitting into smaller groups to forage during the day. In the breeding season, paired birds protect small territories.

Scientists describe this relationship through the social complexity hypothesis. The concept proposes that animals living in intricate social groups may evolve equally intricate communication systems.

Parrots are particularly well suited to this theory: they have large brains, long lifespans, sophisticated social relationships and the ability to learn new vocalisations throughout life.

Types of parrot duets

Once a male and female yellow-naped parrot become a pair, their calls are not random. Instead, they perform coordinated vocal exchanges, taking turns in a pattern.

Known as a duet, this joint display resembles a conversation: one bird calls and its partner responds almost at once.

There are two principal forms of duet. The first, the primary duet, is the less complex version. It contains fewer kinds of calls and follows a more predictable sequence.

Pairs most commonly give primary duets in routine circumstances, particularly in the breeding season while they remain on their territory.

The other form is the warble duet, which is more elaborate. It contains far more call types and is quicker and more intense. The parrots change calls rapidly, and although the sequence can vary considerably, it still operates according to rules.

Investigating the warble duet

“One hypothesis is that maybe warble duets have different notes simply to show their prowess,” Dahlin said.

Yellow-naped parrots employ these more elaborate vocal displays when contesting territory. “So maybe the point is just to have a lot of variety – or maybe it’s something else entirely.”

The researchers aimed to establish whether warble duets were governed by rules comparable to those in human language. Human language relies on two central characteristics: phonology and syntax.

Phonology brings small sounds together to create meaningful units, while syntax governs the order in which those units occur. The team asked whether parrots used comparable organisation.

Recording parrots in Costa Rica

During the breeding months, Professor Dahlin and field assistants recorded parrots in north-west Costa Rica. They used a directional microphone mounted on a tripod, along with a digital video recorder.

From more than 1,000 duet recordings, the researchers chose 52 high-quality warble duets for detailed analysis.

Although each duet lasted only a few seconds, these brief vocal performances contained striking complexity.

Duets with structure

By listening closely to recordings and examining sound patterns on spectrograms, the team compiled a detailed call lexicon. They found 36 primary call types and several uncommon variants – compared with only four call types in standard duets.

The warble duets contained more than 450 individual calls. Repeated tests found that trained observers could classify calls correctly about 92 percent of the time. That level of accuracy indicated that the call categories were dependable.

Around half of all call types were shared by males and females, while the remainder displayed distinct sex differences.

About 31 percent were used mainly by one sex, and roughly 25 percent were exclusive to either males or females.

In every duet, the female produced the first call and the male followed. Calls frequently overlapped with precise timing.

Hidden rules and patterns

To examine syntax, the researchers used Voyant Tools, a computer programme normally employed to analyse human writing. The software identifies collocates: words that regularly occur together. For instance, “eat” and “food” commonly appear together.

The programme identified 19 positive collocates in parrot duets. In other words, particular call types occurred together more frequently than would be expected by chance.

It also revealed four negative associations, showing that certain call types tended to avoid one another.

More than 20 syntactic rules influenced the duets. Although every duet sounded different, its overall structure was directed by recurring patterns.

Of the 52 duets, only two were exact repeats. The majority were unique, and this adaptable framework enabled many possible combinations while retaining rules.

Timed and flexible calls

Some call types occurred predominantly at the start, middle or finish of a duet. Approximately half were positioned in this way.

The remaining calls could occur almost anywhere. Calls with preferred positions did sometimes appear elsewhere, but less frequently.

This combination of organisation and flexibility points to rapid decision-making.

“They’re making multiple decisions,” Dahlin said. “Are they going to duet at all? If so, what kind? And what notes are they giving? All of this is happening very rapidly, and they have to do it in coordination with their partner.”

Possible meanings and functions

Scientists cannot yet demonstrate that every call carries one specific meaning. Some calls, including contact calls, occur in a wide range of situations, suggesting that context may alter their meaning.

Warble duets appear to be associated with active territorial defence. In the wild, physical fights were always preceded by warble duets.

Playback experiments likewise found that parrots produced more warble duets while defending breeding territories.

A broad call repertoire may communicate strength and coordination. Among many songbirds, more elaborate songs are associated with stronger territory defence and higher survival rates. Warble duets may therefore function as forceful warning signals to competitors.

Significance of the research

BirdLife International classifies yellow-naped Amazons as Critically Endangered. Habitat loss and poaching place their populations at risk.

Disruption to social groups can also alter vocal dialects, which are patterns learned culturally.

Learning how wild parrots communicate can support conservation work. Parrots are not merely copying sounds for amusement.

Within Central American forests, these birds depend on structured, rule-bound communication systems that remain flexible yet remarkably complex – rivaling many of the most sophisticated signalling systems found in the animal kingdom.