Dragging a sleigh loaded with enough presents for the world’s children can be no easy skill. But, since ancient times, the Christmas Eve duty has been performed by a team of beloved reindeer.

Soon, however, Santa Claus may have to start looking around for a stronger type of animal, as newresearch shows the species is becoming increasingly puny. A 16-year survey on the arctic Norwegian islands, Svalbard, found the reindeer there have declined in weight by an alarming 12 percent.

The reduction in average body weight is being blamed on global warming. In the research presented lately at a meeting of the British Ecological Society in Liverpool, scientists have explained how upward temperatures are robbing female reindeer of nutrients during important periods of pregnancy.

Snow in Svalbard typically covers the ground for eight months of a year, which, combined with low temperatures, limits grass growth to June and July. But as summer temperatures increase by around 1. 5℃, grass has become more productive, allowing female reindeer to gain more weight by autumn and therefore to have more babies. However, winters have brought with them greater rainfall which freezes when it settles on the snow. Reindeer can often access the poor food sources beneath the snow by clearing it away with their antlers (鹿角) , but they cannot break through the hard ice. As a result, female reindeer are becoming starved, causing them to lose their babies or give birth to the much lighter young.

Despite the findings, reindeer appear to be suffering less from the effect of climate change than some other arctic species. Last week the scientists warned that a third of the world’s polar bears could disappear in the next 40 years.

   Just like humans, birds rely on sound to communicate, too. Often, birds recognize their mates or young by sound rather than sight. Hungry young birds use begging calls to let their mothers know it is feeding time, and warning calls are other sounds given out frequently by the adults. In addition to all these regular calls, some male birds develop beautiful songs intended（打算）to attract the females.

A new study carried out by an American university shows that songbirds practice their songs even in their sleep. The research team discovered that the electrical brain activity of the birds that were asleep was similar to the brain activity produced when the birds were awake and singing. Clearly the bird stores a song after hearing it, then practices it later in its sleep. Scientists now believe the birds dream of songs to help them master the fine art of singing and that sleep plays a key role in the learning process！

It is commonly known that many songbirds learn to sing by listening to adult birds of the same species. If taught the song of an adult of another bird species, the chick grows up singing the new song and passes on the foreign song to its chicks. For instance, researchers carried out an experiment in which a male bullfinch（红腹灰雀）was raised by a female canary（金丝雀）. The bullfinch soon learned the canary's songs and when it was later mated to a female bullfinch, Mr. Bullfinch taught his children the canary's songs.

Early last year, a British survey of London's songbirds showed that the city's birds are losing their melodies. Birds could hardly hear one another over the traffic noise；as a result they had difficulty in learning songs and communicating with potential mates. And instead of copying the sweet notes of the adults, chicks were copying sounds, which they heard most often—namely car horns（喇叭）and mobile phones！

   Winter begins in the north on December 22nd. People and animals have been doing what they always do to prepare for the colder months. Squirrels (松鼠), for example, have been busy gathering nuts from trees. Well, scientists have been busy gathering information about what the squirrels do with the food they collect.

They examined differences between red squirrels and gray squirrels in the American state of Indiana. The scientists wanted to know how these differences could affect the growth of black walnut (黑胡桃) trees. The black walnut is the nut of choice for both kinds of squirrels. The black walnut tree is also a central part of some hardwood forests.

Rob Swihart of Purdue University did the study with Jake Goheen, a former Purdue student now at the University of New Mexico. The two researchers estimate that several times as many walnuts grow when gathered by gray squirrels as compared to red squirrels. Gray squirrels and red squirrels do not store nuts and seeds in the same way. Gray squirrels bury nuts one at a time in a number of places. But they seldom remember where they buried every nut. So some nuts remain in the ground. Conditions are right for them to develop and grow the following spring. Red squirrels, however, store large groups of nuts above ground. Professor Swihart calls “death traps for seeds”.

Gray squirrels are native to Indiana. But Professor Swihart says their numbers began to decrease as more forests were cut for agriculture. Red squirrels began to spread through the state during the past century.

The researchers say red squirrels are native to forests that stay green all year, unlike walnut trees. They say the cleaning of forest land for agriculture has helped red squirrels invade Indiana. Jake Goheen calls them a sign of an environmental problem more than a cause.

   According to a study published last week in the journal Science，scientists have found a way to change a plant's genes（基因）in order to make it use sunlight more quickly. Someday，the results could increase the amount of food produced around the world.

By changing a plant's genes，the scientists were able to increase leaf growth on plants by 14-20 percent. Specifically，scientists changed the plant's protective（保护的）system. “Normally，this system is activated when a plant gets too much sunlight，”said scientist Krishna Niyogi，co-author of the study. “When the plant senses the light，it gets rid of extra energy and creates more leaves. When the plant is in the shade，the protective system is turned off. But the process is slow.”

Stephen Long is the lead author of the study. He compared a plant's protective system to light-adjusting glasses.“When a person wears the glasses outside during the day，the lenses（镜片）darken and lighten depending on how sunny it is. Plants do the same thing，”he said.“But in plants the adjustment can take anywhere from 10 minutes to an hour. This makes it hard for plants to get the right amount of sunlight needed to create food.”

The new study sped up the process. By changing the plant's genes，it's more quickly than normal to turn on and turn off the protective system. As a result，leaf growth on the plants scientists used in the study increased. Leaf growth on two plants increased by 20 percent, while leaf growth on a third plant increased by 14percent. Scientists conducted the study on tobacco plants. But they thought the genetic modification would produce the same results in corn or rice.

Jumping spiders (跳蛛) are vital for agricultural pest control, and 【小题1】 species can even learn to distinguish (辨别) the color red in their prey (猎物), a 2015 study 【小题2】 (show). They are able to learn to associate this color 【小题3】 poisonous prey and avoid it or find out high-quality prey.

Jumping spiders will eat almost any small pest, 【小题4】 (range) from caterpillars to flies. Not only does this 【小题5】 (natural) reduce the amount of agricultural damage from insect pests, but it means farmers can avoid using chemical treatments 【小题6】 (protect) their crops.

In total, a large number of jumping spiders, over 5,000 species, 【小题7】 (find) on every continent except Antarctica by now. Being able to adapt to the environment is a key evolutionary skill. Since the spiders are able to distinguish 【小题8】 foods are nutritious, from those that are 【小题9】 (harm). They can stay alive longer and manage a wide 【小题10】 (various) of pests.