The common rock dove, often dismissed as a mere “city bird,” possesses mental capabilities that continue to surprise cognitive scientists. Pigeons exhibit a sophisticated understanding of abstract concepts, including a fundamental form of mathematics. Research confirms they are capable of numerical discrimination and ordering quantities with an accuracy comparable to that of primates. This exploration reveals that the ability to process numbers is not exclusive to highly evolved mammals, forcing a reevaluation of intelligence and its evolutionary origins.
The Science of Numerosity
For non-human animals, the ability to recognize and distinguish between quantities is called numerosity. This capacity is distinct from human arithmetic, which relies on symbolic language, but it serves as the foundational skill for counting. Pigeons, like many other species, possess two primary systems for apprehending number.
One system, known as subitizing, allows for the immediate and precise recognition of very small quantities, typically one to four items. For larger sets of objects, pigeons rely on the Approximate Number System (ANS). The ANS provides a less precise, ratio-dependent estimate of quantity, meaning distinguishing between two and three items is easier than distinguishing between eight and nine.
Scientists must first establish that a pigeon is responding to the abstract concept of how many rather than to physical cues like total surface area or density of the objects. This ensures that pigeons are truly engaging with number as a distinct dimension, not just physical attributes.
Experimental Proof of Pigeon Counting
To confirm that pigeons recognize numerical quantity, researchers employ sophisticated experimental setups, often using touchscreens. In one classic experiment, pigeons are presented with a visual display containing a specific number of objects, such as dots. The birds must then peck a corresponding key that represents the matching number to receive a food reward.
Scientists control for non-numerical variables to ensure the pigeons are not cheating. The objects on the screen are varied in size, color, shape, and spatial arrangement from trial to trial. This rigorous control ensures the only reliable cue for a correct response is the number of items displayed.
Pigeons also demonstrated their ability to self-generate a number of responses for a reward. Using a Fixed Consecutive Number schedule, birds were trained to peck a key a precise number of times, such as four or sixteen pecks, before switching to a second key. Results showed that pigeons learned to differentiate between these two distinct numerosities, exhibiting an internal mechanism for tracking their own actions.
Comparing Quantities and Ordinality
Beyond recognizing a specific number, pigeons have demonstrated a higher-level ability called ordinality, which is the understanding of sequence or rank. This abstract concept is a major step toward arithmetic thought, as it requires knowing that one number is “less than” or “more than” another in a series.
In a landmark study, pigeons were presented with three images on a touchscreen, each containing one, two, or three objects. The birds were trained to peck the images in ascending numerical order to earn a reward. They consistently learned the abstract rule of the sequence, demonstrating an understanding of the relation between the quantities.
The real test came when researchers presented the trained pigeons with novel pairings of numbers they had never seen before, ranging from one to nine objects. The birds successfully applied the learned rule to the new sets, consistently pecking the smaller quantity first, even for pairs like six and nine. This performance mirrored that of rhesus monkeys tested on the same task, confirming a similar capacity for abstract numerical ordering.
Why This Research Matters
The discovery that pigeons can grasp abstract numerical rules suggests insight into the evolution of cognition. For decades, this ability was thought to be unique to humans and other primates. The common ancestor of birds and mammals lived approximately 300 million years ago, suggesting an enormous evolutionary distance between the two groups.
Finding similar numerical competence in species with vastly different brain structures challenges the notion that a primate-style layered cortex is necessary for this skill. The research suggests that the fundamental number sense is an ancient feature of the vertebrate brain.
This implies that the basic building blocks of mathematical thought evolved much earlier than previously believed or have evolved independently multiple times. The evidence encourages scientists to consider the ability to process quantity as a widespread mechanism for survival across the animal kingdom.