【推荐2】While they can’t pick out precise numbers, animals can comprehend that more is, well, more. From birds to bees and wolves to frogs, animals use numbers to hunt, find a mate, return to their home, and more. Researchers believe that this ability, known as numerical competence, plays an important role in how animals make these decisions. Andreas Nieder, a biologist at the University of Tübingen, explores the current literature on how different animals comprehend numbers.

Honeybees, for instance, can remember the number of landmarks they pass when searching for food in order to find their way back home. This ability can also be seen in animals choosing a larger amount of food over a smaller amount or in animals forming hunting groups. Wolves are more likely to hunt successfully if they have the right number of wolves in their pack for their prey (猎物) with prey like elk (驼鹿), only around six to eight wolves are needed, while hunting wild pigs requires a pack of nine to thirteen. Their prey also uses this concept to protect themselves—elk tend to live in small groups, which rarely have encounters with wolves, or gather in large groups to reduce the chance of any individual becoming prey. “They are assessing the number of individuals in their groups for their everyday life situations,” Nieder says.

Furthermore, numerical competence also plays a role in attracting a mate. For example, male frogs sing “advertisement” calls to attract females. The females, listening to their complicated calls, choose the males that sing the most “chucks” in their calls.

Now researchers do have some sense of the rules that govern numerical competence in animals. For example, they count approximately (大概) rather than specifically and two numbers need to be more different for them to tell them apart as those numbers get bigger. However, Nieder argues that more research needs to be done. “I hope I can encourage behavioral ecologists to specifically explore numerical competence in the wild, and, in doing so, also open new research fields,” he says.

【推荐1】We might think of our eye color as one of our defining physical features, as personal to us as the shape of our nose. But, surprisingly, our eye color doesn’t always remain constant throughout our lives.

Evidence suggests whether a baby’s eye color changes or not depends a lot on the color itself. One study led by American researcher Cassie Ludwig tracked 148 babies born at a hospital in California,recording their iris (虹膜) color at birth. Over half of the babies were born with brown eyes, and less than one-third with blue. Two years later, the researchers found of the 40 blue-eyed babies in the study, l1 had brown eyes by the age of two, three had hazel (浅赤褐色的), and two had green. Of the 77 brown-eyed newborns, almost all (73) still had brown eyes at the age of two.

But why do blue eyes change more? The answer may be found in the fact that when the babies’ eyes did change color, they tended to become darker, not lighter. In Ludwig’s study, one-third of the babies’ eyes changed color in their first two years, with the most common change being eyes becoming darker. The trend towards darkening may be due to the build-up of a protective pigment (色素) in the irises — but more on this later.

Such relatively common, healthy color change is mostly limited to early childhood. In another study in the US, which tracked more than 1,300 twins from babyhood to adulthood, eye color usually stopped changing by the age of six. Among non-identical twins, eye color was more likely to change than among identical twins.

Sometimes color changes can be seen in hair in newborns throughout childhood. “Some babies are born with blonde hair, but they’ve got quite dark brown hair when they become older,” says Australian researcher David Mackey. “That’s probably because the pigment in your hair can increase gradually over time. “It may be a similar story for eye color,” he suggests, with greater quantities of pigment — the main pigment in the eyes is melanin (黑色素) — building up in the months or years after birth.

【推荐2】A large supply of acorns (橡实) on the ground last winter provided food for chipmunks (花栗鼠) across New England in the northeastern US as spring returned. Acorns and other nuts are a main part of the animals’ diet. They also eat insects, berries, and other kinds of fruit. The substantial food supply kept chipmunks well fed as they got busy reproducing and having families this spring. Now, the growth in the chipmunk population is so noticeable, with people saying the animals are driving them nuts.

Shevenell Webb, a biologist with the Maine Department of Inland Fisheries and Wildlife (MDIFW), said： “While chipmunks are often entertaining, they can be a bother.” The animals dig through the ground, making holes and passageways. This can lead to the destruction of grass, flowers and other plant life. Chipmunks can be “cute” and “fun to watch in the forest” as they move in and out of holes like playful children, “When their mouths aren’t full of nuts, chipmunks make an interesting chip sound,” Webb said.

Steven Parren is a wildlife program official with the Vermont Fish & Wildlife Department. He said he couldn’t grow flowers with chipmunks digging them up. “They don’t even cease,” he said. There were so many acorns in one area that there was no way the animals could have put them all away for winter. In addition to chipmunks, he is also seeing more squirrels, rabbits and mice this year.

Experts note while small animal populations can sometimes explode, they usually return to normal. Chipmunks can be food for other creatures. They are easy targets for owls, snakes and foxes. But even if they survive such attacks, Webb said individual chipmunks usually only live about three years. Many New Englanders remember a similar rise in the area’s squirrel population in 2018. Webb said that increase led to a lot of roadkill. “We’ve never seen anything like that. That was a once — in — a — lifetime event.”