When Zero Isn't Nothing: What Animal Zero Cognition Reveals About Your Pet's Mind

TL;DR From rhesus monkeys to honey bees, several species treat “nothing” as a real quantity that sits beside one on a mental number line. The same neural trick may underlie your pet’s ability to notice an empty food bowl. Try three quick brain‑games (shell game, countdown perch, rotating‑bowl quest) to give that skill a workout.

Why zero matters

When we grasp zero, we treat absence as a measurable value that can be ranked, compared, and reasoned with. Cognitive scientists once thought only humans could do this. New experiments show otherwise.

How scientists test for “nothing”

An animal passes the zero test when it:

1. Picks the smaller amount – After learning to choose the lower numerosity, it treats a blank card as “lowest”.
   
   
   

2. Shows the distance effect – It mistakes 0 for 1 more often than for 2, meaning zero sits right next to one in its mental scale.
   
   
   

The surprise line‑up

• Primates – Two rhesus macaques placed empty dot displays at the small end of an ordered sequence and slipped most often between 0 and 1, exactly as predicted. Follow‑up recordings pinpointed “zero‑tuned” neurons in their parietal cortex that fired only when the screen showed no dots, suggesting a specialised neural code for absence.

• Birds – Carrion crows have individual neurons that fire specifically for the empty set; behaviourally they confuse 0 with 1 more than with higher numbers. In lab tests the birds learned to order number cards 0–4, placing the “zero” card consistently at the left‑most end of the sequence.

• Insects – Honey bees trained to pick the smaller pile of shapes flew to a blank target over a one‑dot target and got better as the comparison number grew. Their errors followed the same distance effect seen in vertebrates—most slips between 0 and 1, almost none between 0 and 5—showing a shared analogue number line across phyla.

• Parrots – Alex the African grey once blurted “none” on a counting test, signalling a null set without prompting. Later sessions logged four spontaneous uses of the word in correct contexts, hinting at a grasp of absence rather than rote mimicry.
  
  
  

The appearance of zero‑like processing in species that diverged hundreds of millions of years ago suggests either an ancient neural template or repeated convergent evolution, and scientists are still debating which.

Small brains, big ideas

A honey bee solves relative‑numerosity tasks with about one million neurons—the same order of magnitude as the cells in a single human retina—while a person’s brain deploys 86 billion neurons spread across a cranial volume millions of times larger. Yet the bee crams tens of millions of synapses into that pin‑sized space, runs on mere microwatts of energy, and channels a hefty share of its neural real estate (the mushroom bodies) into flexible learning and number sense.

Researchers now argue that efficient wiring and circuit design, not neuron tally alone, unlock abstract feats like “choose the smaller set.” (Remember, it’s honey bees who gave us the sturdy hexagonal building structure.) Jumping spiders with under 100,000 neurons can plan detours, and honey bees can even spot odd versus even numbers. Where do these all point? That brain power depends on architecture, not bulk.

What this means for your pet

If a bee can reason about nothing, your dog, cat, or cockatiel almost certainly notices when a resource is missing. Enrichment that mimics real‑world choices—Is this bowl empty? Which perch has more seed?—exercises those ancestral circuits, sharpening problem‑solving and lowering stress.

Three at‑home “zero” games

Shell game (dogs, ferrets) – Hide treats under two of three opaque cups. A pet that quickly ignores the empty cup is tracking absence, not just smell.

Countdown perch (parrots, small birds) – Offer three perches with 0, 1, or 2 seeds and shuffle locations each round. Choosing “some but fewer” reveals quantity ranking.

Rotating‑bowl quest (outdoor cats, backyard bees) – Put out three shallow dishes, leave one empty, and rotate the blank daily. Faster avoidance echoes the bee studies.

Keep sessions brief (5–10 min), use high‑value but healthy rewards, and finish on a success to avoid frustration.

Where research heads next

Open questions include why trained crows still stumble when zero appears first in a list, whether reptiles or fish share the skill, and how social living might speed zero learning. Answers could reshape zoo exhibit design, lab‑animal welfare, and everyday pet care.

Further reading

• Quanta Magazine – “Animals Count and Use Zero”

• Live Science – “Crows Understand the Concept of Zero”

• Science – “Numerical ordering of zero in honey bees”