1 . In habitats across the planet, animals periodically drop everything to walk, fly or swim to a new place. Wildlife such as whales and geese learn migration paths by following their parents. Others, including small songbirds, gain the distance and direction of their migration within their genetic code. And some animals use a combination of genetics and culture to guide their migration.

Another group of migrators does not quite fit either model, and researchers have only recently started to figure out how they find their way. Take the Cory’s shearwater, an oceangoing sea bird that migrates over the Atlantic every year. The young do not migrate with their parents, so culture cannot explain their journeys. And the exact paths vary wildly from individual to individual, making genetics equally unlikely.

Cory’s shearwaters are long-lived, rarely producing young successfully before age nine. This leaves an opening for learning and practice to develop their migration patterns. Researchers call this the “exploration-refinement”, and until now it has been hypothetical（假设的）because of difficulties in tracking migratory animals’ movements.

But a team of researchers has done that by attaching small geolocators to more than 150 of the birds aged four to nine. They found that younger birds traveled longer distances, for longer periods, and had more diverse paths than older birds.“We finally have evidence of the ‘exploration-refinement’ for migratory birds,” says Letizia Campioni, who led the study. Younger Cory’s shearwaters are able to fly just as fast as, the adults — but they do not, suggesting that the young do more exploring, which gradually fades as they mature and settle into a preferred course.

Although it may seem less efficient than other strategies, “exploration-refinement could be beneficial to birds and other organisms in a rapidly changing world due to unpredictable man-made changes,” says Barbara Frei. “It might be safer to repeat a behavior that was recently successful than to rely on patterns that were perfected long ago but might no longer be safe.”

6 . Polar bears have captivated(迷住) humans since the beginning of recorded time. Writings dating back to 57 C. E. in ancient Rome describe flooded amphitheatres where polar bears and seals competed against each other ( not much of a fight, as it turns out). Kings of ancient Egypt and early Norway were the first to keep polar bears captive, and the fascination with them has held through the centuries. Ad campaigns all over the world feature polar bears to sell everything from bottled water to transportation systems to soda.

A Coca-Cola ad campaign in the 1990s added "adorable" to the polar bear's image. The ads featured a clumsy, animated cub that bridged the natural wariness between polar bears and penguins to share a nice, cold bottle of Coke. Polar bears don't actually have a natural affinity for penguins, as the two don't live in any of the same regions and never see each other. But still, cute is cute.

Polar bears' shocking whiteness, ferocity and sheer size make them icons of purity and power. Males can grow up to 10 feet tall (3 meters) and weigh up to 1,500 pounds (680 kilograms). A single bear can take on a 2,500-pound walrus, and hang on to the massive catch with 2-inch claws (5 centimeters). They walk hundreds of miles across ice sheets every winter, following their prey.

In the Arctic, polar bears are at the top of the food chain, and it’s not just because of their size. They're so well-adapted to their environment that they experience no change in body temperature at minus 34 degrees Fahrenheit ( minus 37 Celsius). However, the incredible survival mechanisms that let them thrive in frigid winters may prove to be their undoing. Because of global warming, winters are getting less cold and polar bears are dying. Some scientists project that if climate trends continue, 30 percent of the current polar bear population will be wiped out by 2050. What’s life like for an animal that needs such extreme cold to survive? Let's head to the Arctic and see how polar bears live on the ice.

7 . Plants are boring. They just sit there photosynthesizing （光合作用） while animals have all the fun. Right? Not so much. A new study has found that there is a long history of interactions between ants and plants. The ant and plant co-evolution （协同进化） started with ants feeding on plants and plants evolving ant-friendly features.

Plants make a number of different structures that are specific for ant use. Some plants have evolved features that persuade ants into defending them from attack from other insects and even mаmmаlѕ. Тhеѕе іnсludе hollow thorns that аntѕ will live іnѕіdе, or ехtra nесtаr (琼浆) оn lеаvеѕ or stems for the ants to eat. Some ants will just cheat and take the nectar and run, but some will stick around and attack anything that tries to hurt the plant. Other plants get ants to help them move their seeds around, by providing them with rich food packets attached to the seeds. The ant will pick up the seed and carry it away, eat the food packet, and leave the seed - often in a nutrient-rich area where it'll grow better, and since it's farther away from its parent, they won't have to compete for resources.

But scientists weren't sure how the evolutionary relationship between ants and plants got started. If evolution is an arms race between species developing ways to make use of their neighbors, then scientists wanted to know whether plants or ants fired the first shot. It was a chicken-and-egg question, whether things started with ants developing behaviors to take advantage of plants, or plants evolving structures to take advantage of ants.

The history of ants and plants evolving together goes back to the time of the dinosaurs, and it's not easy to tell from fossils who fired the first shot. However, it is a question of little significance. Scientists say their study maters because it provides a look at how these widespread and complex interactions evolved.