Chimpanzee Food Calls Reveal Surprisingly Detailed Secrets About Hidden Food

In the dense forests and captive colonies where chimpanzees live out their daily lives, one of the most common sounds is a burst of rough, throaty grunting when an individual discovers food. For decades, researchers regarded these so-called food calls as little more than emotional leakage — an involuntary expression of excitement that said something about how much the caller wanted the food, but little else. A new playback experiment, published in the journal Animal Cognition, upends that comfortable assumption. The study, led by Stuart K. Watson of the University of Zurich together with colleagues including Katie E. Slocombe of the University of York, Klaus Zuberbühler and Josep Call of the University of St Andrews, and Simon W. Townsend of the University of Zurich, demonstrates that chimpanzee food calls carry a degree of acoustic specificity that has, until now, been documented almost exclusively in alarm call systems. Listeners, the findings show, can extract not only how valuable a food is, but which particular food the caller has found.

Functionally referential signals — vocalizations that reliably inform listeners about specific external events or objects — have long fascinated comparative psychologists because they blur the boundary between animal communication and human language. Vervet monkeys emit distinct alarm calls for leopards, eagles and snakes, and recipients respond appropriately to each. Prairie dogs embed information about predator features in their calls, and some birds encode details about food quality. But the question of just how fine-grained these references can be has remained open. Most documented referential systems distinguish broad categories: predator versus non-predator, high-value versus low-value food. Whether a signal can pick out individual food types within a category — whether a chimp’s grunt for bread sounds meaningfully different from its grunt for mango — had never been empirically tested for chimpanzee food calls.

Chimpanzees produce rough grunts when finding and eating food, and earlier work had established that the acoustic structure of these calls varies with the preference value of the food that elicits them. Grunts given to highly preferred foods differ systematically from those given to less desirable items, and subsequent research showed that listening chimpanzees can use this variation to guide their own foraging decisions. That established a meaningful baseline: the calls encode relative preference. What remained unknown was whether the specificity stopped there. If two foods are both highly preferred — say, bread and mango — do the grunts they elicit sound the same to a listener, or do they carry information distinguishing one food from the other? And critically, does that fine-grained information actually matter to receivers, or is it merely acoustic noise that no chimpanzee attends to?

To answer these questions, the research team, whose work was supported by the Biotechnology and Biological Sciences Research Council and by the Swiss National Science Foundation through the NCCR Evolving Language programme, combined two complementary approaches. The first was a careful acoustic analysis of food calls recorded from chimpanzees at the Wolfgang Köhler Primate Research Centre in Leipzig, Germany, where calls elicited by foods of matched preference values could be compared. The second was a playback experiment — a technique in which recorded vocalizations are broadcast to an animal while researchers observe how it responds — allowing the team to test whether the acoustic distinctions they detected were actually meaningful to a listening chimpanzee rather than incidental by-products of arousal.

The acoustic analysis produced a strikingly layered picture. The calls differed between foods of high and low preference value, replicating and extending the earlier findings that grunts track how much a caller likes what it has found. But the analysis went further: significant acoustic differences also emerged between individual food types within each of those preference categories. In other words, grunts elicited by different high-value foods could be statistically discriminated from one another, and so could grunts elicited by different low-value foods. The calls were not simply graded along a single dimension of excitement. Instead, they appeared to encode at least two distinct dimensions of information simultaneously — the general value of the food and its specific identity — a combination that suggests a far richer encoding system than anyone had demonstrated in chimpanzee feeding vocalizations.

Statistically detectable differences, however, do not automatically translate into communicative relevance. An acoustic signature can reflect physiological differences in arousal, jaw position, or food texture in the mouth without any listener ever extracting information from it. This is where the playback design proved decisive. The researchers broadcast recorded food calls to a chimpanzee subject and measured the responses, focusing on whether the animal’s behaviour indicated that it had interpreted the calls as information about what lay hidden at the playback location. By pairing calls recorded in one context with search opportunities in another, the experiment isolated the informational content of the vocalization itself from any direct sensory experience of the food.

The results were remarkable on all three fronts. The listening chimpanzee discriminated between calls elicited by high-value and low-value foods, confirming once again that preference information is accessible to receivers. More importantly, the subject also discriminated between calls elicited by individual types of high-value food, and between calls elicited by individual types of low-value food. The fine-grained distinctions that showed up in the acoustic analysis were not lost on the audience: the receiver behaved as though it knew not just that something good had been found, but what kind of good thing it was. This represents, the authors write, an unprecedented degree of specificity in the referential food calls of our closest living relatives — a level of detail previously identified only in alarm call systems, not in feeding vocalizations.

The theoretical implications ripple outward in several directions. For theories of language evolution, the finding narrows the perceived gap between primate vocal communication and human speech. One cornerstone of linguistic meaning is the ability of a signal to pick out specific referents rather than broad emotional states, and this study shows that chimpanzee calls can do something analogous with food types, not just food categories. It also challenges the long-standing division between ‘referential’ alarm calls and ’emotional’ food calls: if food calls encode specific identities in a way receivers use, the referential-emotional dichotomy looks increasingly like a human-imposed simplification rather than a real feature of chimpanzee communication. The study adds to a growing body of evidence that the vocal repertoire of great apes is far more structured than the behaviorist traditions of the twentieth century assumed.

The methodology deserves attention too. Combining acoustic analysis with playback experiments is the gold standard for demonstrating functional reference, because each approach compensates for the other’s weaknesses. Acoustic analysis can reveal structure that receivers ignore; playback can reveal comprehension of differences the analysis missed. By requiring both — statistically discriminable calls and demonstrably different receiver responses — the researchers built a case that is difficult to dismiss. The work was approved by the School of Psychology Ethics committee at the University of St Andrews, and the authors declare no competing interests. The study was published open access, with a citable, permanent DOI, meaning anyone can examine the evidence in full.

Questions naturally remain. The playback tested a single subject, so the generality of comprehension across individuals and communities will need confirmation. It is also unclear how the specificity arises — whether callers intentionally vary their grunts to inform others, whether the acoustic differences emerge as side effects of eating different foods, or whether listeners have simply learned to exploit regularities in the sounds. None of this diminishes the central result: chimpanzees listening to a distant group member’s grunts can apparently learn both how desirable a hidden food is and what that food actually is. For a species separated from our own lineage by roughly six million years, that is a strikingly sophisticated channel of information, and it suggests that the seeds of referential specificity run far deeper in the primate lineage than the study of alarm calls alone had ever revealed.

Subject of Research: Referential specificity of chimpanzee food calls tested through acoustic analysis and playback experiments

Article Title: Chimpanzee food calls provide information about the value and type of food: a playback study

Article References: Watson, S. K., Kaller, T., Cheng, L., Wathan, J., Townsend, S. W., Zuberbühler, K., Call, J., & Slocombe, K. E. (2026). Chimpanzee food calls provide information about the value and type of food: a playback study. Animal Cognition. https://doi.org/10.1007/s10071-026-02105-w

Image Credits: AI Generated

DOI: 10.1007/s10071-026-02105-w

Keywords: chimpanzees, food calls, functional reference, rough grunts, playback experiment, vocal communication, animal cognition, primatology, language evolution, acoustic analysis, foraging behaviour, referential signalling