托福机经：2013年3月16日托福阅读机经_第2页

　　Do not be fooled however, being cold blooded does have its advantages as well.  For instance, cold blooded animals require much less energy to survive than warm blooded animals do.  Mammals and birds (warm blooded creatures) require much more food and energy than do cold blooded animals of the same weight.  This is because in warm blooded animals, heat loss from their bodies is proportional to the surface area of their bodies, while the heat created by their bodies is proportional to the surface area of their bodies, the heat created by their bodies is proportional to their mass.

　　Furthermore, the ratio of a body’s surface area to its mass is less the larger the anima is.  What this means is that larger, warm blooded animals are able to generate more heat than they lose and more easily able to keep their body temperatures stable.  This in turn also makes it easier form them to stay warmer by being larger.  This also means that if a warm blooded animal is toop small it will lose its heat faster than it can produce it.  Since cold blooded animals don’t need to burn as much food to maintain a constant body temperature, they are more energy efficient and can survive longer periods of time without food than warm blooded creatures can.  Many cold blooded creatures will try to keep their body temperatures as low as possible when food is scarce.

　　Cold blooded creatures also have the advantage of being less prone to infections than warm blooded animals.  This lies in the fact that being a warm blooded body provides a warm environment for viruses, bacteria and parasites to reside.  As a general rule, mammals and birds since they are warm blooded, are usually prone to more problems with infections and such than reptiles, whose constantly changing body temperature make life more difficult for bacteria, etc. to survive in.

　　Mammals do however; still have a stronger immune system than cold blooded animals.  A reptile’s immune system is more efficient when the animal is warmer, however since bacteria are known to most likely grow slower in lower temperatures, reptiles will sometimes lower their body temperatures when they have an infection.

　　3、动物迁徙时脑海中的方位指示动物迁徙时如何找到方向。举了一种蝴蝶，冬天长，迁徙，夏天到，产卵，死亡，两三代后飞回。动物们如何辨别方向，方法一二三：看coast line， 鲸鱼跃出水面vertical，看星星之类 动物们为了适应太阳和天体的变化，自己有一个mechanical timing要随时调节，但是有一种鸟不用。如果阴天怎么办，鸽子可以根据地磁来飞行，相信以后会有更多的研究表明地磁很重要。

　　Monarch Migration[ //en.wikipedia.org/wiki/Monarch_(butterfly)]

　　Monarchs are especially noted for their lengthy annual migration. In North America, they make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. The monarch is the only butterfly that migrates both north and south as the birds do on a regular basis, but no single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations.

　　By the end of October, the population east of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve within the Trans-Mexican Volcanic Belt pine-oak forests in the Mexican states of Michoacán and México. The western population overwinters in various sites in central coastal and southern California, United States, notably in Pacific Grove, Santa Cruz, and Grover Beach.

　　The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a nonreproductive phase known as diapause, which may last seven months or more. During diapause, butterflies fly to one of many overwintering sites. The overwintering generation generally does not reproduce until it leaves the overwintering site sometime in February and March.

　　The overwinter population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. The second, third and fourth generations return to their northern locations in the United States and Canada in the spring. How the species manages to return to the same overwintering spots over a gap of several generations is still a subject of research; the flight patterns appear to be inherited, based on a combination of the position of the sun in the sky and a time-compensated Sun compass that depends upon a circadian clock based in their antennae. New research has also shown these butterflies can use the earth's magnetic field for orientation. The antennae contain cryptochrome, a photoreceptor protein that is sensitive to the violet-blue part of the spectrum. In the presence of violet or blue light, it can function as a chemical compass, which tells the animal if it is aligned with the earth's magnetic field, but it is unable to tell the difference between the magnetic north or south.

　　The complete magnetical sense is present in a single antenna. Monarch butterflies are one of the few insects capable of making trans-Atlantic crossings. They are becoming more common in Bermuda due to increased usage of milkweed as an ornamental plant in flower gardens. Monarch butterflies born in Bermuda remain year round due to the island's mild climate. A few monarchs turn up in the far southwest of Great Britain in years when the wind conditions are right, and have been sighted as far east as Long Bennington. In Australia, monarchs make limited migrations in cooler areas, but the blue tiger butterfly is better known in Australia for its lengthy migration. Monarchs can also be found in New Zealand. On the islands of Hawaii, no migrations have been noted.

　　Monarch butterflies are poisonous or distasteful to birds and mammals because of the presence of the cardiac glycosides contained in milkweed consumed by the larvae. The bright colors of larvae and adults are thought to function as warning colors. During hibernation, monarch butterflies sometimes suffer losses because hungry birds pick through them looking for the butterflies with the least amount of poison, but in the process kill those they reject.

　　One study examined wing colors of migrating monarchs using computer image analysis, and found migrants had darker orange (reddish-colored) wings than breeding monarchs.

　　Research also has overturned a prevailing theory that the migration patterns of the eastern and western populations are due to genetic reasons and that their genetic material was different. The American populations have been found to be distinct from the populations in New Zealand and Hawaii, but not from each other.