While working in Louisiana, psychologist Claudia Uller, of the University of Essex, UK, tested the numerical abilities of a local amphibian, the red-backed salamander.



When tasked with picking between two fruit-fly-filled tubes, the animals could tell the difference between 1, 2 and 3 flies, but not between 3 and 4.



They also discriminated between larger numbers of flies; up to 16 so far.



However, they could only do this if the ratio between the number of flies in each tube was greater than 2 to 1.



(Image: Brian Gratwicke)

Experiments in newborn chicks show that they have an innate sense of number.



A team lead by Rosa Rugani and Lucia Regolin, at the University of Padova, Italy, found that chicks duped into believing balls or scraps of paper are their kin can perform simple addition and subtraction.



(Image: Rosa Rugani / University of Trento)

Clever Hans was a German horse that wowed European crowds in the early 1900s.



He was apparently able to stamp out the answers to maths problems.



However, a scientific trial later proved that Hans was reacting to the subconscious body cues of his trainer, and not actually counting. Advertisement

American coots can be tricked into raising the eggs of other coots.



To combat this, they only add up their own eggs when determining how many more to lay - ignoring any rogue eggs that may have turned up.



(Image: David Berner, Edmonton, Alberta)

Overwhelming evidence now suggests that other primates have a sense of number that is similar to our own.



For instance, when tasked with picking the larger of two groups of dots flashed onto a computer monitor, rhesus monkeys and university students both make fewer errors when the ratio between the two groups of dots is large.



“The student’s performance ends up looking just like a monkey's. It’s practically indistinguishable,” says Elizabeth Brannon, a psychologist at Duke University, who led many of the studies.



(Image: Wally Koscielny / Living Color Studios)

Mosquitofish also seem to rely on ratio in order to count.



Christian Agrillo and colleagues at the University of Padova found that, when tasked with swimming to the larger of two shoals, the fish can discriminate between numbers up to 16.



However, they can only do so if the ratio between the fish in each shoal is greater than 2 to 1.



They also represent smaller numbers precisely, discriminating between 1, 2, 3 and 4.



(Image: Christian Agrillo / University of Padova)

Elizabeth Brannon has been leading the research into the cognitive behavior of lemurs, including showing that they can perform numerical cognition.



Brannon uses a mix of computer touchscreens (left) and physical, sequential experimenter tests.



She has shown that mongoose lemurs have numerical representations that are modulated by Weber's Law - an equation that attempts to describe how changes in the real world (like the size of a number) are reflected in changes in perceived, subjective intensity.



She has also shown that ringtailed lemurs (Lemur catta) can represent ordinal relations - that is, put numbers in order of size - much like monkeys.



(Image: Elizabeth Brannon / Duke University)