Being able to count may be innate to many species. An article in New Scientist featured 8 amazing animals that are able to count or distinguish between ratios. Here are their stories:
Red-backed salamanders: Dr. Claudie Uller at the University of Essex, UK tested the counting ability of these amphibians in Louisiana. The animals were able to pick out tubes containing 1, 2, or 3 flies but could not tell the difference between 3 and 4 flies. If the ratio of flies in each tube was greater than 2 to 1, they could also discriminate up to 16 flies in each tube.
Newborn chicks: Rosa Rugani and Lucia Regolin from the University of Padova, Italy discovered that chicks have the ability to add and subtract small numbers.
American coots: These animals can be the victims of brood parasites, which are birds that lay eggs in another bird's nest to trick it into raising their offspring. The coots are able to count their own eggs and ignore any that may have been deposited by a brood parasite.
Primates: Many primates have a similar ability to count as humans and make similar errors as college students when instructed to choose the larger group of dots shown on a computer screen if there is a large difference between the groups of dots.
Mosquitofish : Christian Agrillo and colleagues from the University of Padova discovered that these fish could count up to 4 and were able to correctly swim to a larger shoal of fish comprised of up to 16 animals, but could only distinguish differences in the size of shoals if the ratio between them was greater than 2 to 1.
Lemurs: Dr. Elizabeth Brannon at Duke University has demonstrated that these animals process numbers. Mongoose lemurs process numbers using Weber's Law, which describes how changes in the real world are perceived by the animals. Similar to monkeys, ringtailed lemurs have the ability to arrange numbers in the correct sequence.
Honeybees: Dr. JÃ¼rgen Tautz and colleagues demonstrated that bees could tell the difference between groups of 1 and 2, 2 and 3, as well as 3 and 4 shapes. They apparently can count up to 5.
Another article, published in Scientific American shortly after the first, talked about birds that could count:
Alex, the African grey parrot: Can count up to 6 and is able to add and subtract.
Wild New Zealand robins: Dr. Kevin Burns and colleagues from Victoria University of Wellington in New Zealand, discovered these birds could count. With the birds watching, the researchers made holes in fallen logs and placed different numbers of mealworms in each hole. The birds chose the holes with the most mealworms. If the birds were tricked by removing some the worms outside of their line of sight, then they spent time searching the holes for the missing mealworms. They reportedly have the ability to be trained to count up to 12.
Know of any other animals that can count, please let us know!
Other studies include lions, horses, beetles, angelfish, guppies and of course lots of non-human primates (btw, lemurs are primates).
The study investigating the larger numbers in salamanders did not investigate Plethodon cinereus , nor were flies used as stimuli (and Dr. Uller is not the first author).