Pūkeko use sound elements to create calls and combine them to create complex call sequences in order to expand the range of options for expressing themselves – these are the findings of an international team including Konstanz researchers. Until now, this behaviour had only been known in vocal learning animals, such as primates, whales or songbirds.
Humans have a whole alphabet of options to communicate with each other. We combine individual letters – or, more precisely, phonetic elements – to form words that we put together in sentences according to grammatical rules. This allows us to explain complex matters and gives us virtually unlimited options for creating new meanings. Similar to humans and for anatomical reasons, animals' vocal apparatuses can only express a limited number of sounds.

To find out whether pūkeko (Porphyrio melanotus melanotus) combine individual sound elements of their repertoire to communicate with each other, a team of researchers from the Cluster of Excellence "Collective Behaviour" at the University of Konstanz conducted a study recently published in Animal Behaviour. The team identified two organizational tiers in pūkeko communication – calls and call sequences – that each have their own combination rules. Until now, this kind of complexity in combining sounds had only been known in vocal learners, animals that change and adjust their vocal expressions over the course of their lives. These animals include, for example, primates, whales or songbirds – but not rails, such as the pūkeko.

Listening in
In order to understand the underlying rules for pūkeko communication, the researchers hid miniature audio recorders in the nests of 17 pūkeko groups and recorded all of the sounds the animals made over the course of several days. Afterwards, the team manually identified and classified the sounds in the audio material. "In order to recognize individual sound elements, we not only listened for the sounds, but also watched graphical representations of the audio signals – or spectrograms. This enabled us to increase the reliability of our analysis", explains Gabriella Gall, first author of the study, and a researcher from the Konstanz Cluster of Excellence "Collective Behaviour". "Overall, we were able to isolate well over 5000 high signal to noise ratio sound elements in our recordings that were assigned to thirteen different types of sounds."

In a next step, the researchers took a closer look at the order of these sound elements over time. They found that about a third of the sound elements occurred mainly on their own. The remaining ones appeared mostly in combination with other elements. Particular rules guided how such sound elements were combined to form calls: Some sound elements appear mainly at the beginning of a call, others at the end or – in calls consisting of more than two elements – most likely in the middle. The call length also plays a role, so that some sound elements change their preferred position or are no longer used in calls of greater length.

From calls to call sequences
But that's not all: The combination options are even more complex. Using yelling sequences that pūkeko express in aggressive contexts as an example, the Konstanz researchers show that only nine of the thirteen identified sound elements occur in these aggressive call sequences – and only in particular segments. Another rule that emerged: The longer the sequence, the greater the number of calls per unit of time. Calls also become longer and change their structure as additional sound elements are included and the variability of the call composition increases.

The researchers surmise that sound elements that always appear alone each fulfil their own independent communicative function. However, elements that are used as pre- or suffixes, at the beginning or end of a call sequence respectively, modify the information content of the sound elements in between them. "The subsequent organization of the calls on a second hierarchical level – the level of call sequences – suggests that pūkeko have a very sophisticated, structured communication system. We had not seen this before in animals that, like pūkeko, use the same sound repertoire for their entire lives", Gall says.

The researchers also have an initial understanding of the function and rules of this additional, second hierarchical level. For example, the information included in the final part of the call sequence could refer to the context that was defined at the beginning of the sequence. In addition to this, variations in call structure could convey information about changes in the corresponding animals' state of arousal. "Our next goal is to find out the exact meaning of sound elements and their combinations", Gall adds.

Key facts:

• Original publication: G.E.C. Gall, V. Demartsev, P. Minasandra, C. Baldoni, K.E. Cain, J.S. Quinn (2026) Examining combinatoriality within the pūkeko vocal repertoire. Animal Behaviour; doi: 10.1016/j.anbehav.2025.123431
• An international research team comprised mainly of Konstanz-based researchers from the Cluster of Excellence "Collective Behaviour" studies the acoustic communication of pūkeko (Porphyrio melanotus melanotus).
• Pūkeko communication has two organizational levels – calls and call sequences – and thus exhibits a complexity that was not known, until now, in animals like the pūkeko.
• The Cluster of Excellence "Collective Behaviour" at the University of Konstanz is a global hotspot for the study of collective behaviour across a wide range of species and across scales of organization.
• Funding: German Research Foundation (DFG) and Zukunftskolleg at the University of Konstanz