Turtles have a habit of eating plastic objects floating in the sea, which may kill them. Many believe that it is because floating plastic bags look similar to jellyfish, which many types of turtles love to eat. However, lots of plastic objects that turtles eat do not look like jellyfish at all. Joseph Pfaller of the University of Florida doubts that the smell of sea micro-organisms (微生物) which live on floating plastic objects attract turtles to eat.

The kind of idea first appeared in 2016. Researchers at the University of California, Davis, noticed that certain chemicals, especially dimethyl sulphide (二甲基硫), which can be found on plastics where micro-organisms live, are those which many seabirds sniff (嗅) to find food. These birds are more likely to eat plastics.

Since turtles usually appear above the sea surface and sniff the air when going to their feeding areas, Dr. Pfaller believed that they are following these same chemicals like those seabirds and mistakenly think that floating plastic objects are edible.

To test that idea, he and his team did an experiment using loggerhead turtles. They exposed 15 turtles to four smells: the smell of clean water; the smell of turtle-feeding food; the smell of a clean plastic bottle; and the smell of a bottle that had been kept in the ocean for five weeks to allow micro-organisms to grow on it. When sniffing both the smell of turtle-feeding food and that of five-week-old bottles, turtles kept their noses out of the water more than three times as long, and took twice as many breaths as they did when sniffing the smell of fresh bottle-plastic or clean water.

Though they have not yet tested whether dimethyl sulphide on the five -week-old bottles cause turtles to cat plastic objects, Dr. Pfaller and his team think it is highly possible.

Dogs in the classroom lower stress of primary school students, new research has found. The study by UK researchers found spending some time with a dog twice a week was better for reducing stress on students than many other classroom relaxation activities. And the benefits of these “dog dates" were similar for children in both normal and special schools.

Stress is known to negatively affect a child’s learning, behaviour, health and mood. This has led schools to try a number of ways to reduce stress, including yoga, mindfulness, physical activities and even having animals in classrooms.

The researchers from the University of Lincoln measured students' stress levels by tracking the level of the stress in their saliva (唾液). They studied 105 students aged 8 to 9 in four normal schools as well as 44 children of a similar age in seven special schools in the UK. The children were randomly (任意) divided into three groups: a group that spent time with a dog; a group that spent time doing relaxation activities; and a “control” group that did neither of these things. Students in the dog group spent 20 minutes with a trained dog twice a week for four weeks. The relaxation group spent the same amount of time doing exercises.

The researchers found that the children in the dog group had “significantly lower” stress levels, while those in the relaxation and control groups recorded an increase over the school term. The study, which was published in the journal PLOS ONE, also found stress was lowest in the children in the dog group immediately after their contact with the puppies. “Dog-assisted activities can lead to lower stress levels in schoolchildren with and without special educational needs,” University of Lincoln researcher Kerstin Meints said, “but more research is needed to discover what was the ideal amount of time and contact with dogs for the best effect.”

There is a vivid world beyond our senses that wildlife knows in ways human cannot. A hummingbird sees colors that humans can only imagine. Elephants call to each other in bass rumbles too deep for human hearing, Bumblebees sense the electrical field of flowers ripe for pollination, while sea turtles feel the planet’s magnetic pull.

Working on the top of the Rocky Mountains, scientists for the first time proved that wild hummingbirds can see ultraviolet light (紫外线) invisible to humans. Researchers led by Mary Stoddard at Princeton University tested wild broad-tailed hummingbirds in their natural setting and clearly showed the birds use their ultraviolet vision to search for food.

Biologists have long known that many birds have eyes sensitive to ultraviolet light, but they did not know how it might affect their vision or their natural behavior. To find out, Dr Stoddard and her colleagues went to the Rocky Mountain Laboratory, a high-altitude breeding ground for broad-tailed hummingbirds. There the scientist set up two special feeding stations equipped with LED displays which can emit UV colors, such as ultraviolet green. One feeder, emitting a UV color, contained the sugar water that hummingbirds long for, while the other, emitting a non-UV shade of the same color, contained plain water.

During the three years of filed test, birds visited the feeders 6000 times. Once they learned the clue, their ability to distinguish UV and non-UV colors accurately guided them to the sugar water, no matter how often the researchers switched them around or changed colors. “We could see the humming birds learning there was a difference between colors that looked absolutely identical to us. And that was extremely exciting,” Dr Stoddard says.

Dr Stoddard and her colleagues then tested 3.300 examples of plumage and plants. About a third of them had displayed ultraviolet colors. In nature, color conveys more than eye appeal: Color is a clue of information ——about food, mates or predators.