A Duke University-led study finds that bottlenose dolphins burn calories at a lower rate as they get older, just like humans do. It’s the first time that scientists have measured an age-related metabolic(新陈代谢的) slowdown in another large-bodied species besides humans, said the first author Rebecca Rimbach.

Rimbach has studied energy consumption in animals ranging from mice to monkeys. But data on the inner workings of sea animals such as dolphins and whales have been scant, she says. “That’s because these ocean animals are difficult to catch for repeated measurement. It can be very tricky to get the animal back when you need it,” Rimbach said.

The researchers studied 10 bottlenose dolphins aged 10 to 45 living at two sea animal centers. To measure their average daily metabolic rates, the researchers used the “doubly labeled water method”. It involved getting the dolphins to drink a few pounds of water with “heavy” forms of hydrogen and oxygen put in, and then following how long they took to force them out. Carers collected the dolphins blood and analyzed the levels of heavy hydrogen and oxygen atoms(原子) in it. Thus, the team was able to count how much carbon dioxide (CO₂) the dolphins produced each day, and then how many calories they were burning as they went about their lives.

The scientists found the oldest dolphins in the study, both in their 40s, used 22% to 49% fewer calories each day than expected for their body weight. And similar to humans, more of those calories ended up as fat rather than muscle. Dolphins in their 40s had body fat percentages that were 2.5 times higher than the under-20 dolphins’. It wasn’t for lack of exercise and it wasn’t because they’re eating too much, Rimbach said. It was related to metabolic aging.

The researchers said such work could uncover factors besides diet and lifestyle that caused age-related weight gain in people. “Further studies into this commonality we share with dolphins may help us understand why our metabolism slows as we age,” said co-author Hannah Salomons.

If you were bringing friends home to visit, you could show them the way. You know the landmarks — a big red house or a bus-stop sign. But what if you were swimming in the middle of the Atlantic Ocean? Could you still find your way home？A loggerhead turtle（海龟）could.

According to Dr. Ken Lohmann, loggerheads have a magnetic（磁力的）sense based on Earth's magnetic field. It helps them locate the best spots for finding food and their home beaches.

Scientists already know that several other animals, such as whales and honeybees, can detect（探测到）magnetic fields. The difference between them and loggerheads, however, is the way they learn to use their magnetic sense. Young whales and honeybees can learn from adults. Loggerheads are abandoned as eggs.

As newborn loggerheads have no adults to learn from, what helps them figure out how to use their magnetic sense? Lohmann thinks one of the cues was light on the sea.

Baby loggerheads hatch only at night. However, a small amount of light reflects off the ocean. The light makes that region brighter. Heading toward the light helps them get quickly out to sea, where they can find food. Lohmann tested whether newborn loggerheads use this light source to set their magnetic “compasses”（罗盘）. He and his team put some newborns in a water tank and recorded which way they swam. Around the tank,   the scientists created a magnetic field that matched the Earth’s. They set a weak light to the east of the magnetic field. Then they let the newborns go.

At first, the newborns swam toward the light. After the scientists turned off the light, the turtles that had seen the light in the east always swam toward east. When the researchers reversed（颠倒）the magnetic field, these turtles turned around and swam toward the new "east".

This and the follow-up experiments all showed that loggerheads use light from the outside world to set their magnetic "compasses" and then remember the "correct" direction. If a turtle hatches on a brightly-lit beach, that would damage its magnetic sense forever and make survival hard for the turtle.

Lohmann's work has led others to protect the habitat of this endangered species. Yet many questions about these creatures remain unanswered, and researchers have a lot to study.

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.