Enlarge / Clown anemonefish ( Amphiprion ocellaris ) seem to recognize different species of clownfish by counting white stripes. (credit: Kina Hayashi)

Many people tend to think of clownfish, with their distinctive white bars against an orange, red, or black background, as a friendly sort of fish, perhaps influenced to some extent by the popular Pixar film Finding Nemo . But clownfish can be quite territorial when it comes to defending their host anemone from intrusion by others, particularly those from their own species. A new paper published in the Journal of Experimental Biology describes how clownfish determine if a fish approaching their home is friend or foe by "counting" the number of white bars or stripes on their bodies.

As previously reported , mathematical ability is often considered uniquely human, but in fact, scientists have found that many animal species —including lions, chimpanzees, birds, bees, ants, and fish—seem to possess at least a rudimentary counting ability or number sense. Crows can understand the concept of zero. So can bees, which can also add and subtract, as can both stingrays and cichlids —at least for a small number of objects (in the range of one to five). Some ants count their steps .

This so-called "numerosity" simply refers to the number of things in a set, according to cognitive psychologist Brian Butterworth, an emeritus professor at University College London and author of Can Fish Count? What Animals Reveal About Our Uniquely Mathematical Minds . It has nothing to do with reasoning or logical mathematical intelligence. This is information that will be in the environment, and counting animals must have some mechanism for extracting this numerical information from the environment. But it nonetheless makes for a fascinating field of study.

Enlarge / Look at this very good boy taking a test to determine the origin of his spatial bias for a study on how dogs think. (credit: Eniko Kubinyi)

Research has shown that if you point at an object, a dog will interpret the gesture as a directional cue, unlike a human toddler, who will more likely focus on the object itself. It's called spatial bias, and a recent paper published in the journal Ethology offers potential explanations for why dogs interpret the gesture the way that they do. According to researchers at Eötvös Loránd University in Hungary, the phenomenon arises from a combination of how dogs see (visual acuity) and how they think, with "smarter" dog breeds prioritizing an object's appearance as much as its location. This suggests the smarter dogs' information processing is more similar to humans.

The authors wanted to investigate whether spatial bias in dogs is sensory or cognitive, or a combination of the two. "Very early on, children interpret the gesture as pointing to the object, while dogs take the pointing as a directional cue," said co-author Ivaylo Iotchev . "In other words, regardless of the intention of the person giving the cue, the meaning for children and dogs is different. This phenomenon has previously been observed in dogs using a variety of behavioral tests, ranging from simple associative learning to imitation, but it had never been studied per se."

Their experimental sample consisted of dogs used in a previous 2018 study plus dogs participating specifically in the new study, for a total of 82 dogs. The dominant breeds were border collies (19), vizslas (17), and whippets (6). Each animal was brought into a small empty room with their owner and one of the experimenters present. The experimenter stood 3 meters away from the dog and owner. There was a training period using different plastic plates to teach the dogs to associate either the presence or absence of an object, or its spatial location, with the presence or absence of food. Then they tested the dogs on a series of tasks.

Cats have a well-deserved reputation for being independent-minded and aloof, preferring to interact with humans on their own quirky terms. So you'd never see a cat playing fetch like a dog, right? Wrong. That sort of play behavior is more common than you might think—one of our cats was an avid fetcher in her younger years, although she's slowed down a bit with age. However, the evidence to date for specific fetching behaviors in cats is largely anecdotal.

That's why a team of British scientists set out to study this unusual feline play behavior more extensively, reporting their findings in a new paper published in the journal Scientific Reports. The researchers concluded that most cats who like to play fetch learned how to do so without any explicit training and that cats are generally in control when playing fetch with their humans. Specifically, cats will play fetch longer and retrieve the thrown object more times when they initiate the game rather than their owners. In other words, cats are still gonna be cats.

Many different animal species exhibit play behavior, according to the authors, and it's most common in mammals and birds. When cats play , their behavior tends to resemble hunting behavior commonly seen in European wildcats and lynxes: rapid approach and retreat, leaping, chasing, pouncing, and stalking. Initially, as kittens, they engage in more social forms of play with their littermates like wrestling, and they tend to engage in more solitary play as adults—the opposite of dogs, who usually start playing with objects alone before transitioning to social play.

The key to a successful sleight-of-hand magic trick is how well a magician manipulates the audience's perception, especially of manual movements, since that is crucial to how we anticipate another's actions. To learn more about how humans experience such misdirection, researchers in the UK performed simple magic tricks for three species of monkeys to see if they could be fooled. They found that only those species with at least partially opposable thumbs were fooled, suggesting that having similar anatomy (and therefore biomechanical ability) plays a vital role in the illusion. They described their results in a new paper published in the journal Current Biology.

“Magicians use intricate techniques to mislead the observer into experiencing the impossible," said co-author Elias Garcia-Pelegrin , who practices magic and conducted this research while completing his PhD at the University of Cambridge. "It is a great way to study blind spots in attention and perception. By investigating how species of primates experience magic, we can understand more about the evolutionary roots of cognitive shortcomings that leave us exposed to the cunning of magicians. In this case, whether having the manual capability to produce an action, such as holding an item between finger and thumb, is necessary for predicting the effects of that action in others.”

The researchers focused on three species with different hand anatomies and associated biomechanical abilities: yellow-breasted capuchin monkeys, Humboldt's squirrel monkeys, and common marmosets. For instance, capuchins are known for their manual dexterity, due in part to the fact that they can individually control their fingers. So they can perform a scissor grip (holding an object between the sides of two fingers), as well as a precision grip (bringing the thumb to the index or middle finger). They can even probe, pinch, or enclose an object with both hands, much like humans, and use stone tools to crack nuts.

Enlarge / Bumblebees can learn to solve puzzles from experienced peers. Honeybees do the same to learn their waggle dances. (credit: Diego Perez-Lopez, PLoS/CC-BY 4.0 )

Social insects like bees demonstrate a remarkable range of behaviors, from working together to build structurally complex nests (complete with built-in climate control) to the pragmatic division of labor within their communities. Biologists have traditionally viewed these behaviors as pre-programmed responses that evolved over generations in response to external factors. But two papers last week reported results indicating that social learning might also play a role.

The first, published in the journal PLoS Biology, demonstrated that bumblebees could learn to solve simple puzzles by watching more experienced peers. The second , published in the journal Science, reported evidence for similar social learning in how honeybees learn to perform their trademark "waggle dance" to tell other bees in their colony where to find food or other resources. Taken together, both studies add to a growing body of evidence of a kind of "culture" among social insects like bees.

"Culture can be broadly defined as behaviors that are acquired through social learning and are maintained in a population over time, and essentially serves as a 'second form of inheritance,' but most studies have been conducted on species with relatively large brains: primates, cetaceans, and passerine birds," said co-author Alice Bridges , a graduate student at Queen Mary University of London who works in the lab of co-author Lars Chittka . "I wanted to study bumblebees in particular because they are perfect models for social learning experiments. They have previously been shown to be able to learn really complex, novel, non-natural behaviors such as string-pulling both individually and socially."

Specific breeds of dogs, like border collies, can learn the verbal names of their favorite toys, but what is going on in the dog's mind when it's told to fetch a given toy? According to a recent paper published in the journal Animal Cognition, these dogs store key sensory features about their toys—notably what they look like and how they smell—and recall those features when searching for the named toy.

"If we can understand which senses dogs use while searching for a toy, this may reveal how they think about it," said co-author Shany Dror , a biologist at Eotvos Lorand University in Budapest, Hungary. "When dogs use olfaction or sight while searching for a toy, this indicates that they know how that toy smells or looks like."

Prior studies suggested that dogs typically rely on vision, or a combination of sight and smell, to locate target objects. Few dogs can also identify objects based on verbal labels, which the authors call "gifted word learner" (GWL) dogs. "Just like humans, GWL dogs not only recognize the labeled objects—or categories of objects—as stimuli they have already encountered, but they also identify them among other similarly familiar named objects, based on their verbal labels," the authors wrote. They wanted to investigate whether GWL dogs have an enhanced ability to discriminate and/or recognize objects compared to typical dogs.

Enlarge (credit: Aurich Lawson)

We often think of mathematical ability as being uniquely human, but in fact, scientists have found that many animal species —including lions, chimpanzees, birds, bees, ants, and fish—seem to possess at least a rudimentary counting ability or number sense. Crows can understand the concept of zero. And a study published in April found that both stingrays and cichlids can take this rudimentary "numerosity" to the next level, performing simple addition and subtraction for a small number of objects (in the range of 1 to 5).

The latter study's conclusion doesn't surprise cognitive psychologist Brian Butterworth, an emeritus professor at University College London and author of a new book, Can Fish Count? What Animals Reveal About our Uniquely Mathematical Minds .

"There are lots of animals that can do addition and subtraction," Butterworth told Ars. "Bees can. Bees can represent zero as well. So it's not surprising to me that stingrays and cichlids can do it." His book explores how the ability to process mathematical information and extract numerical data from their environment is critical to an animal's ability to survive and thrive. In fact, there might just be an innate understanding of math at its most basic level that was passed down the evolutionary chain from our most distant common ancestors.