Say you’re a small mammal like a ground squirrel, vulnerable to becoming a bigger animal’s meal. You spy a roomy cave in the distance—but two large bears are already heading into it. A few minutes later, one walks out. Is the cave safe for you? That’s the kind of real-time calculation most animal species face on a daily basis.
In addition to avoiding predators, the ability to grasp quantity can help solve a range of problems, such as finding a mate, foraging, and navigating.
Now, in one of the most sweeping analyses to date, a scientist has brought together all the research on the subject and found that, from bees to birds to wolves, many animals have an ability to process and represent numbers—arguably a form of counting.
What's more, the new study suggests that this mathematical prowess helps animals stay alive in a brutal world. Such a finding extends our knowledge of animal cognition, a field that has grown exponentially in recent years. (Read more about how animals can think or feel—just like us.)
“Counting abilities were once thought to be a uniquely human skill, perhaps because of the perceived association of advanced mathematical ability and genius,” says Lars Chittka, a behavioral ecologist at Queen Mary University of London who wasn’t involved in the research.
But the research, published in the new issue of Trends in Ecology and Evolution, “shows that basic numerical abilities are very widespread in the animal kingdom, and can be advantageous in the struggle for survival.”
Good with numbers
For the study, neurobiologist Andreas Nieder, at the University of Tuebingen in Germany, explored the current literature on how different animal species comprehend numbers.
After perusing nearly 150 scientific articles on the subject, he concluded that “numerical competence is present on almost every branch on the animal tree of life.”
Not surprisingly, his review showed that many species rely on numbers to find food.
In laboratory studies, for instance, oriental fire-bellied toads depend on a method called the “approximate number system” to choose between various clusters of food. To the frogs, a cluster of three items was as good a choice as four, but when the numbers changed to three vs. six, or four vs. eight, they always selected the cluster with the larger number.
Honeybees have been shown to remember the number of landmarks as they travel from their hives to a field of flowers, so that they can find their way back home. And the desert ant Cataglyphis fortis counts its steps to track how far it’s traveled from its nest on foraging trips.
Other species, such as gray wolves, need to know the right number of animals in their pack to hunt specific prey. Six to eight wolves are necessary when hunting elk and moose, for example, while a bison hunt requires a pack of nine to 13. (Read how black bears can “count.”)
Their prey also use numbers to their advantage; elk disperse in smaller herds to avoid encountering wolves, or gather in large herds to reduce their chances of becoming the victim, a tactic described in biology as “safety in numbers.”
Fight or flight
Many species need to assess the strength and relative number of opponents before engaging in a fight for territory or for a mate.
Take prides of female African lions, which are known to listen closely to the roars of other nearby prides before choosing whether to battle. In one classic experiment in Tanzania’s Serengeti National Park, a pride heard recordings of a single unknown female intruder roaring, which prompted the lions to go on the attack. (Read more about the short and happy lives of Serengeti lions.)
But if the pride heard recordings of three or more other lions vocalizing, they hesitated. The best predictor of whether the lions chose to approach was the ratio of the number of adult defenders to the number of intruders.
“Obviously, they’re assessing the number of individuals in their groups for their everyday life situations,” Nieder says. “So the capability to discriminate numbers has to have a strong survival and reproduction benefit.”
Karl Berg, an ornithologist at the University of Texas Rio Grande Valley in Brownsville, agrees that many animals have “sophisticated ways of measuring or estimating abundance.”
For instance, he has observed young female green-rumped parrotlets in Venezuela leaving the area where they hatched, while the males stayed put. Some years, the opposite occurs.
“Whether they decide to stay or go depends on the abundance of food and the sex ratio,” meaning how many males there are versus females, Berg says. “It’s absolutely fascinating that they can estimate something like that. We don’t know how they do it.”
“What’s important in all of these studies is to figure out how numerical competency is connected to fitness—that is, an animal’s lifetime reproductive success,” he cautions.
In his study, Nieder calls for more of such studies, but conducting them is difficult and time-consuming, Berg says. “These can only be done in the wild, if you’re to have truly meaningful results.”