於鳥類遷徙：由於鳥類遷徙時(shí)遇到陰天就停下來，好像分不請(qǐng)方向，所以科學(xué)家predict 鳥類遷徙靠太陽指引方向。做實(shí)驗(yàn)，用artifical sun 取代 real sun，鳥依然朝artifical sun飛?？茖W(xué)家作試驗(yàn)看食物是不是另外一種guide導(dǎo)致鳥類的遷徙。結(jié)果發(fā)現(xiàn)鳥類能否找到食物完全依賴光線，也就是視覺。也就是說食物不能促使鳥類遷徙。另外一個(gè)試驗(yàn)又證明夜晚遷徙的鳥類靠star 來定位。另外一個(gè)在什麼天文館做的試驗(yàn)又證明夜晚遷徙的鳥類靠star 來定位。後面是一個(gè)同類的實(shí)驗(yàn)。但是鳥類在向著artifical sun 飛行時(shí)，每小時(shí)會(huì)變換方向15度角，而這也是真實(shí)的太陽方向變化的速度，估計(jì)是由鳥類自身生物鐘引起的。鳥的生物鐘直接與太陽光強(qiáng)弱有關(guān)，白天遷徙的鳥類根據(jù)在太陽光線的強(qiáng)弱飛行的距離，太陽下山前鳥類一定會(huì)準(zhǔn)時(shí)到達(dá)其預(yù)定地點(diǎn)。附帶還記得考的單詞：prediction, core, offset...
Animal migration
Humpback whales and blue whales make long migrations. They spend the summer in polar oceans, which have plentiful food. In the autumn, they swim toward the equator until they reach the warm tropical seas. There, the females that are pregnant give birth.
Migration Birds Know No Boundaries
The migration of birds is one of the most fascinating and least understood events in nature.
Arctic terns are the champions of long-distance migration. They fly about 11,000 miles (17,700 kilometers) from their breeding grounds in the Arctic to their winter home in the Antarctic.
Why birds migrate
In many parts of the world, the foods that birds eat become scarce during certain seasons of the year. Most birds would starve if they had to remain in such places through the unfavorable season.
Although birds migrate to survive, the factors that actually trigger their migrations are much more difficult to explain. For example, many northern species leave their summer home while the weather is still warm and the food supply plentiful.
Bird migrations are probably regulated by the glandular system. The glands produce chemical substances called hormones.
Changes in hormone production stimulate the birds to migrate. Among some northern species, hormone production is affected by the length of daylight. As the daylight hours shorten, hormonal changes cause the birds to prepare for their migratory flight south.
Birds’ Sense of direction
The question of how migrating birds find their way to the same destination every year has long puzzled and fascinated scientists.
Scientific research has provided several answers to this question. For example, birds that migrate by day follow various landmarks, such as river valleys and mountain ranges.
Experiments have shown that some birds navigate by the stars. Many scientists believe that certain other birds are guided by the earth's magnetic field.
However, discoveries like these raise even more puzzling questions. To navigate by the stars or to be guided by the earth's magnetic field, birds must have highly specialized and highly complicated sensory organs. But scientists do not know what these sensory organs are or how they function.
Princeton biologist Wikelski has found that birds rely on a built-in magnetic compass, which they recalibrate each evening based on the direction of the setting sun.
To maintain that heading throughout the night, they sense the Earth’s magnetic field, just like a pilot uses a compass at night or in bad weather.
答案：桑。
Animal migration
Humpback whales and blue whales make long migrations. They spend the summer in polar oceans, which have plentiful food. In the autumn, they swim toward the equator until they reach the warm tropical seas. There, the females that are pregnant give birth.
Migration Birds Know No Boundaries
The migration of birds is one of the most fascinating and least understood events in nature.
Arctic terns are the champions of long-distance migration. They fly about 11,000 miles (17,700 kilometers) from their breeding grounds in the Arctic to their winter home in the Antarctic.
Why birds migrate
In many parts of the world, the foods that birds eat become scarce during certain seasons of the year. Most birds would starve if they had to remain in such places through the unfavorable season.
Although birds migrate to survive, the factors that actually trigger their migrations are much more difficult to explain. For example, many northern species leave their summer home while the weather is still warm and the food supply plentiful.
Bird migrations are probably regulated by the glandular system. The glands produce chemical substances called hormones.
Changes in hormone production stimulate the birds to migrate. Among some northern species, hormone production is affected by the length of daylight. As the daylight hours shorten, hormonal changes cause the birds to prepare for their migratory flight south.
Birds’ Sense of direction
The question of how migrating birds find their way to the same destination every year has long puzzled and fascinated scientists.
Scientific research has provided several answers to this question. For example, birds that migrate by day follow various landmarks, such as river valleys and mountain ranges.
Experiments have shown that some birds navigate by the stars. Many scientists believe that certain other birds are guided by the earth's magnetic field.
However, discoveries like these raise even more puzzling questions. To navigate by the stars or to be guided by the earth's magnetic field, birds must have highly specialized and highly complicated sensory organs. But scientists do not know what these sensory organs are or how they function.
Princeton biologist Wikelski has found that birds rely on a built-in magnetic compass, which they recalibrate each evening based on the direction of the setting sun.
To maintain that heading throughout the night, they sense the Earth’s magnetic field, just like a pilot uses a compass at night or in bad weather.
答案：桑。