The list below highlights research papers that observe symbolic thinking across animal species in the wild, without any prior human training or conditioning. I think it is valuable to have such a list, primarily to show that humans are not the only animals with the capability for symbolic thought, and to show that these animal species demonstrate symbolic thought without any prior human training.
Secondly, I think this list is a useful tool for further researchers, and I finally see it as resource that enables us to conduct some simple analysis.
For example, symbolic thinking was observed across three biological classes:
Mammals:
- Primates: Chimpanzee, Rhesus Macaque, Vervet Monkey
- Cetaceans: Bottlenose Dolphin
- Proboscideans: African Elephant
- Carnivorans: Meerkat
- Rodents: Gunnison’s Prairie Dog
Birds:
- Corvids: Carrion Crow
- Passerines (Songbirds): Japanese Great Tit, N.Z. Robin, Green-rumped Parrotlet
- Galliformes: Domestic Chicken
Insects:
- Honeybee
- Desert Ant
It is also interesting note that all observed animal species are highly social. Further, some of them are complex communicators, some have learned to use tools and some are cooperative survivors.
Complex Communicators:
- Vervet Monkeys (famous for specific alarm calls for different predators).
- Honeybees (the “waggle dance” to communicate distance and direction).
- Gunnison’s Prairie Dogs (highly sophisticated vocalizations describing size/color of threats).
- Green-rumped Parrotlets (use “names” or signature contact calls).
Tool Users and Problem Solvers:
- Chimpanzees and Carrion Crows (renowned for creating and using tools).
- Bottlenose Dolphins (highly social, self-aware, and creative hunters).
Cooperative Breeders / Survivors:
- Meerkats (strict social hierarchy and sentinel behavior).
- African Elephants (matriarchal societies with deep social memory).
Finally, we can do a brain-body comparison to see if the size of the animal’s brain has to do with the emergence of symbolic thinking.
For this, we can use the Encephalization Quotient (EQ): A measure that compares an animal’s actual brain size to the “expected” brain size for its body mass. A score of 1.0 is average; higher means “extra” brain power for complex tasks.
| Animal | Brain Mass (approx) | Body Mass (approx) | EQ / Ratio Note |
| Human | 1,350 g | 70 kg | 7.4 – 7.8 |
| Bottlenose Dolphin | 1,600 g | 170 kg | 5.3 |
| Chimpanzee | 400 g | 50 kg | 2.2 – 2.5 |
| Carrion Crow | 12 g | 0.5 kg | 2.5 |
| Rhesus Macaque | 90 g | 7 kg | 2.1 |
| Vervet Monkey | 60 g | 5 kg | 1.7 |
| African Elephant | 5,000 g | 6,000 kg | 1.7 – 2.4 |
| Japanese Great Tit | 0.7 g | 15 g | 0.9 |
| Meerkat | 6.5 g | 730 g | 0.7 |
| N.Z. Robin | 0.8 g | 35 g | 0.6 |
| Prairie Dog | 6.5 g | 900 g | 0.6 |
| Domestic Chicken | 3 g | 2 kg | 0.1 |
| Honeybee | 0.002g | 0.1g | <0.1 |
Raw brain size doesn’t tell the whole story. While the Elephant has the largest brain on the list (5kg!), its EQ is lower than a Crow’s because a huge portion of its brain is dedicated simply to managing its massive body and trunk. The Crow and Dolphin are “over-brained” for their size, which is a hallmark of high cognitive flexibility. Honeybees and Desert Ants show that you don’t need a huge brain to be “smart.”
Note: The papers are listed chronologically form the most recently published to the latest.
1. Crows Recognize Geometric Regularity
Author(s): Schmidbauer, P., et al.
Year: 2025
Species: Carrion Crow (Corvus corone)
Abstract / Key Findings:
Crows trained to detect “intruders” in visual arrays spontaneously applied this rule to novel geometric shapes, exhibiting a “regularity effect” where they performed better with Euclidean shapes (squares) than irregular ones. This suggests an unlearned, intuitive grasp of geometric concepts.
Link: Crows recognize geometric regularity | Science Advances
2. African Elephants Address One Another with Individually Specific Name-like Calls
Author(s): Pardo, M. A., et al.
Year: 2024
Species: African Elephant (Loxodonta africana)
Abstract / Key Findings:
Machine learning analysis of wild elephant rumbles revealed that individuals address one another with arbitrary vocal labels (“names”) that do not mimic the receiver’s calls. Elephants responded preferentially to playback of their “names,” indicating a capacity for abstract, symbolic labeling.
3. Numerical Cognition in Honeybees Enables Addition and Subtraction
Author(s): Howard, S. R., et al.
Year: 2019
Species: Honeybee (Apis mellifera)
Abstract / Key Findings:
Honeybees were trained to use color as a symbolic operator (blue for addition, yellow for subtraction) in a Y-maze. They successfully applied these rules to novel numbers, demonstrating that an insect brain can manipulate symbolic representations of arithmetic operations.
Link: Numerical cognition in honeybees enables addition and subtraction | Science Advances
4. Experimental Evidence for Compositional Syntax in Bird Calls
Author(s): Suzuki, T. N., et al.
Year: 2016
Species: Japanese Great Tit (Parus minor)
Abstract / Key Findings:
This study demonstrated that wild birds combine distinct call types (ABC for “scan”, D for “approach”) into ordered sequences (ABC-D) to elicit compound behaviors. Reversing the call order disrupted the response, providing evidence for compositional syntax in a non-human species.
Link: Experimental evidence for compositional syntax in bird calls | Nature Communications
5. Addition and Subtraction in Wild New Zealand Robins
Author(s): Garland, A., & Low, J.
Year: 2014
Species: N.Z. Robin (Petroica longipes)
Abstract / Key Findings:
Using a violation-of-expectancy paradigm in the wild, researchers showed that robins look longer when the number of prey items revealed does not match the arithmetic outcome of a subtraction event. This proves spontaneous arithmetic ability without human training.
Link: Addition and subtraction in wild New Zealand robins – ScienceDirect
6. The Meanings of Chimpanzee Gestures
Author(s): Hobaiter, C., & Byrne, R. W.
Year: 2014
Species: Chimpanzee (Pan troglodytes)
Abstract / Key Findings:
Researchers cataloged the gestural repertoire of wild chimpanzees, identifying specific gestures used consistently to achieve distinct social goals. This study argues that ape gestures are intentional and carry specific meanings, unlike many vocalizations which are often tied to emotional states.
Link: The Meanings of Chimpanzee Gestures: Current Biology
7. Vertical Transmission of Learned Signatures in a Wild Parrot
Author(s): Berg, K. S., et al.
Year: 2012
Species: Green-rumped Parrotlet (Forpus passerinus)
Abstract / Key Findings:
This field study demonstrated that wild parrot nestlings learn their specific “signature” contact calls from their parents. It provided crucial evidence that vocal labeling in parrots is a socially learned, culturally transmitted trait rather than an innate vocalization.
Link: Vertical transmission of learned signatures in a wild parrot | Proceedings B | The Royal Society
8. Prairie Dog Alarm Calls Encode Labels About Predator Colors
Author(s): Slobodchikoff, C. N., et al.
Year: 2009
Species: Gunnison’s Prairie Dog (Cynomys gunnisoni)
Abstract / Key Findings:
Field experiments showed that prairie dogs produce acoustically distinct alarm calls for humans wearing different colored shirts (blue vs. yellow). The calls encode specific descriptive information, functioning as a combinatorial, descriptive language acquired in the wild.
Link: Prairie dog alarm calls encode labels about predator colors | Animal Cognition
9. Arithmetic in Newborn Chicks
Author(s): Rugani, R., et al.
Year: 2009
Species: Domestic Chicken (Gallus gallus)
Abstract / Key Findings:
Newly hatched chicks, imprinted on specific sets of objects, were able to track the displacement of those objects behind screens. They consistently chose the screen hiding the larger number of items, performing basic addition and subtraction purely based on observation.
Link: Arithmetic in newborn chicks | Proceedings B | The Royal Society
10. Motivation Before Meaning: Motivational Information Encoded in Meerkat Alarm Calls Predator Colors
Author(s): Manser, M. B., et al.
Year: 2007
Species: Meerkat (Suricata suricatta)
Abstract / Key Findings:
This study showed that meerkats encode both predator type and urgency in their alarm calls. It demonstrated how referential information can emerge from motivational states, providing a bridge between emotional signaling and symbolic communication.
11. Signature Whistle Shape Conveys Identity Information to Bottlenose Dolphins
Author(s): Janik, V. M., et al.
Year: 2006
Species: Bottlenose Dolphin (Tursiops truncatus)
Abstract / Key Findings:
This study confirmed that dolphins use “signature whistles” to broadcast individual identity, encoded in the frequency modulation pattern independent of voice features. It demonstrated that dolphins recognize these arbitrary frequency contours as labels for specific individuals.
Link: Signature whistle shape conveys identity information to bottlenose dolphins
12. The Ant Odometer: Stepping on Stilts and Stumps
Author(s): Wittlinger, M., et al.
Year: 2006
Species: Desert Ant (Cataglyphis fortis)
Abstract / Key Findings:
By manipulating leg lengths (stilts vs. stumps), researchers proved that desert ants “count” their steps to measure distance traveled. While not symbolic in the linguistic sense, it demonstrates a precise internal numerical integration mechanism used for navigation in the wild.
Link: https://www.science.org/doi/10.1126/science.1126912
13. Spontaneous Number Representation in Semi-Free-Ranging Rhesus Monkeys
Author(s): Hauser, M. D., et al.
Year: 2000
Species: Rhesus Macaque (Macaca mulatta)
Abstract / Key Findings:
Semi-free-ranging monkeys were tested on their ability to predict the outcome of subtraction events (e.g., 2 plums minus 1 plum). The monkeys successfully discriminated between correct and incorrect outcomes, providing early evidence for spontaneous arithmetic competence in primates.
Link: Spontaneous Number Representation in Semi-Free-Ranging Rhesus Monkeys on JSTOR
14. Monkey responses to three different alarm calls: Evidence of predator classification and semantic communication
Author(s): Seyfarth, R. M., et al.
Year: 1980
Species: Vervet Monkey (Chlorocebus pygerythrus)
Abstract / Key Findings:
The foundational study establishing that vervet monkeys use distinct alarm calls for different predators (leopard, eagle, snake) which trigger specific escape behaviors. This provided the first robust evidence for “functionally referential” communication in wild primates.
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