Benefits of Migration
Why do animals migrate? One obvious answer is to escape cold weather by moving to a warmer region. Each fall, millions of monarch butterflies migrate southward from the central and eastern regions of Canada and the United States to fir forests in central Mexico-sites with particular characteristics that enable the survival of the butterflies. These forests are found about 3,000 meters above sea level on the southwest slopes of a very small area of mountaintops. An important characteristic of these forests is that their temperature is cool but not freezing. Exposure to freezing temperatures would kill the monarchs. However, warmer temperatures would unnecessarily elevate their metabolic rates and waste energy reserves.
Another characteristic of these overwintering sites that enhances the survival of monarchs is the tall trees, primarily oyamel firs. Besides providing branches on which the butterflies can roost (settle for rest or sleep) in large numbers, the trees form a thick, protective canopy over the butterflies. The canopy serves as an umbrella, shielding the butterflies from rain, snow, or hail. This increases survival because a dry monarch can withstand colder temperatures better than one with water on its surface can. If monarch butterflies are wet, 50 percent of the population will freeze at -4.2°C. If they are dry, however, the temperature can dip to-7.7C before 50 percent of the population freezes. The canopy also serves as a blanket that keeps the butterflies warm. Openings in the forest canopy increase cooling, which can lower body temperatures to as much as 4C below the surrounding air temperature. The body temperature of monarchs under a dense canopy is approximately the same as the air temperature. However, body temperature drops in proportion to the degree of exposure, increasing the chances that the butterflies will freeze to death.
Seasonal changes in climate also affect food supply. In some species, migration is an adaptation that permits the exploitation of temporary or moving resources. The larvae (immature forms) of monarch butterflies feed only on milkweed. In regions of the eastern United States, however, the milkweed plants grow only during the spring and summer months. Certain species of insect-eating bats may migrate in response to the size of the insect supply. Mexican free-tailed bats, for instance, leave the southwestern United States as the harsh winter climate causes the insect supply to dwindle. They migrate to regions of Mexico where insects are available throughout the winter.
As winter approaches, increasing the animals’ energy needs, the food supply drops and forces any resident species into more severe competition for such commodities. So, in spite of the energy required for migration, it may result in an overall energy savings. For example, a study of the dickcissel revealed that despite the energy costs of migration, this bird enjoys an energy advantage from both its southward fall migration and its northward spring migration. Studies of the junco, white- throated sparrow, and American tree sparrow show that by avoiding the temperature stresses of northern winters, these species compensate for at least some of the energy spent on migration.
The question arises, then, if there is so much food in the warmer winter habitats, why do species migrate from such areas? Why do they return to their summer homes at all? One answer might be that there are important advantages in rearing broods (offspring) in the summer habitats. For example, days in the far north are long, and the birds working day can be extended-they can bring more food to their offspring in a given period of time and perhaps rear the brood faster. Another result of long days is that more food is available for offspring and more young can be raised. Although factors other than food availability may also play a role, generally the farther north from the tropics a species breeds, the larger is its brood.
Some species migrate to areas that provide the necessary conditions for breeding or that offer some protection from predators. Gray and humpback whales, for example, breed in coastal bays and lagoons that provide the warmer temperatures needed for calving and help protect the calves from predation. The need for protected breeding sites may prompt seal, sea lion, and walrus migrations, as these animals come ashore on their traditional beaches after months at sea.
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Why do animals migrate? One obvious answer is to escape cold weather by moving to a warmer region. Each fall, millions of monarch butterflies migrate southward from the central and eastern regions of Canada and the United States to fir forests in central Mexico-sites with particular characteristics that enable the survival of the butterflies. These forests are found about 3,000 meters above sea level on the southwest slopes of a very small area of mountaintops. An important characteristic of these forests is that their temperature is cool but not freezing. Exposure to freezing temperatures would kill the monarchs. However, warmer temperatures would unnecessarily elevate their metabolic rates and waste energy reserves.
The word “elevate” in the passage is closest in meaning to
Vocabulary Questions词汇题
Achange
Baffect
Climit
Draise
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Why do animals migrate? One obvious answer is to escape cold weather by moving to a warmer region. Each fall, millions of monarch butterflies migrate southward from the central and eastern regions of Canada and the United States to fir forests in central Mexico-sites with particular characteristics that enable the survival of the butterflies. These forests are found about 3,000 meters above sea level on the southwest slopes of a very small area of mountaintops. An important characteristic of these forests is that their temperature is cool but not freezing. Exposure to freezing temperatures would kill the monarchs. However, warmer temperatures would unnecessarily elevate their metabolic rates and waste energy reserves.
According to paragraph 1, temperatures in fir forests allow monarch butterflies to do all the following EXCEPT
Negative Factual Information Questions否定事实信息题
Aenjoy a habitat similar to that found in eastern regions of Canada and the United States
Bavoid freezing to death
Cfunction at normal metabolic rates
Davoid wasting energy reserves
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Another characteristic of these overwintering sites that enhances the survival of monarchs is the tall trees, primarily oyamel firs. Besides providing branches on which the butterflies can roost (settle for rest or sleep) in large numbers, the trees form a thick, protective canopy over the butterflies. The canopy serves as an umbrella, shielding the butterflies from rain, snow, or hail. This increases survival because a dry monarch can withstand colder temperatures better than one with water on its surface can. If monarch butterflies are wet, 50 percent of the population will freeze at -4.2°C. If they are dry, however, the temperature can dip to-7.7C before 50 percent of the population freezes. The canopy also serves as a blanket that keeps the butterflies warm. Openings in the forest canopy increase cooling, which can lower body temperatures to as much as 4C below the surrounding air temperature. The body temperature of monarchs under a dense canopy is approximately the same as the air temperature. However, body temperature drops in proportion to the degree of exposure, increasing the chances that the butterflies will freeze to death.
In paragraph 2, why does the author provide information about the conditions under which 50 percent of the population of monarch butterflies will freeze?
Factual Information Questions事实信息题
ATo emphasize the importance of the canopy formed by the oyamel fir forest to the survival of monarch butterflies
BTo suggest that the effect of snow on monarch butterflies is more significant than that of rain
CTo identify how wet and dry conditions affect temperature at the overwintering sites of monarch butterflies
DTo explain why monarch butterflies roost in large numbers
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Seasonal changes in climate also affect food supply. In some species, migration is an adaptation that permits the exploitation of temporary or moving resources. The larvae (immature forms) of monarch butterflies feed only on milkweed. In regions of the eastern United States, however, the milkweed plants grow only during the spring and summer months. Certain species of insect-eating bats may migrate in response to the size of the insect supply. Mexican free-tailed bats, for instance, leave the southwestern United States as the harsh winter climate causes the insect supply to dwindle. They migrate to regions of Mexico where insects are available throughout the winter.
According to paragraph 3, why do Mexican free-tailed bats leave the southwestern United States in the winter?
Factual Information Questions事实信息题
ATo allow the size of the insect supply to increase
BTo follow the monarch butterflies
CTo find insects to feed on
DTo avoid freezing to death in the harsh winter climate
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As winter approaches, increasing the animals’ energy needs, the food supply drops and forces any resident species into more severe competition for such commodities. So, in spite of the energy required for migration, it may result in an overall energy savings. For example, a study of the dickcissel revealed that despite the energy costs of migration, this bird enjoys an energy advantage from both its southward fall migration and its northward spring migration. Studies of the junco, white- throated sparrow, and American tree sparrow show that by avoiding the temperature stresses of northern winters, these species compensate for at least some of the energy spent on migration.
The word “compensate” in the passage is closest in meaning to
Vocabulary Questions词汇题
Asave up
Bmake up
Callow
Davoid the need
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The question arises, then, if there is so much food in the warmer winter habitats, why do species migrate from such areas? Why do they return to their summer homes at all? One answer might be that there are important advantages in rearing broods (offspring) in the summer habitats. For example, days in the far north are long, and the birds working day can be extended-they can bring more food to their offspring in a given period of time and perhaps rear the brood faster. Another result of long days is that more food is available for offspring and more young can be raised. Although factors other than food availability may also play a role, generally the farther north from the tropics a species breeds, the larger is its brood.
According to paragraph 5, which of the following is NOT one of the reasons why birds may return to their summer habitats?
Negative Factual Information Questions否定事实信息题
AThere are more sunlight hours in which to look for food
BThere is more food available on which to raise the young.
CExtended working days allow birds more time to prepare homes for their offspring.
DMore offspring can be produced at once.
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Some species migrate to areas that provide the necessary conditions for breeding or that offer some protection from predators. Gray and humpback whales, for example, breed in coastal bays and lagoons that provide the warmer temperatures needed for calving and help protect the calves from predation. The need for protected breeding sites may prompt seal, sea lion, and walrus migrations, as these animals come ashore on their traditional beaches after months at sea.
According to paragraph 6, some sea animals migrate to breeding sites that provide which of the following?
Factual Information Questions事实信息题
AEscape from very warm temperatures
BRest after spending months at sea
CDeep waters for calving
DProtection from predators
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Some species migrate to areas that provide the necessary conditions for breeding or that offer some protection from predators. Gray and humpback whales, for example, breed in coastal bays and lagoons that provide the warmer temperatures needed for calving and help protect the calves from predation. The need for protected breeding sites may prompt seal, sea lion, and walrus migrations, as these animals come ashore on their traditional beaches after months at sea.
Which of the following can be inferred from paragraph 6 about the behavior of seals, sea lions, and walruses?
Inference Questions推理题
AUnlike gray and humpback whales, they are poor at avoiding predators.
BThey give birth to their young on beaches.
CThey can only remain at sea for short periods of time.
DThey prefer to breed in coastal bays and lagoons.
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Another characteristic of these overwintering sites that enhances the survival of monarchs is the tall trees, primarily oyamel firs. Besides providing branches on which the butterflies can roost (settle for rest or sleep) in large numbers, the trees form a thick, protective canopy over the butterflies. The canopy serves as an umbrella, shielding the butterflies from rain, snow, or hail. This increases survival because a dry monarch can withstand colder temperatures better than one with water on its surface can. [■] If monarch butterflies are wet, 50 percent of the population will freeze at -4.2°C. If they are dry, however, the temperature can dip to-7.7C before 50 percent of the population freezes. [■]The canopy also serves as a blanket that keeps the butterflies warm. [■]Openings in the forest canopy increase cooling, which can lower body temperatures to as much as 4C below the surrounding air temperature. [■]The body temperature of monarchs under a dense canopy is approximately the same as the air temperature. However, body temperature drops in proportion to the degree of exposure, increasing the chances that the butterflies will freeze to death.
Look at the four squares [■]that indicate where the following sentence could be added to the passage
However, some canopy characteristics could be harmful to the butterflies.
Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
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Animals migrate seasonally for a variety of reasons.
Prose Summary Questions概要小结题
Select 3 answers
AMonarch butterflies migrate thousands of kilometers to mountain habitats that provide ideal temperature ranges and oyamel firs for shelter.
BIn winter, the food supply decreases at the same time that energy demands increase, causing many species of birds and some bats to migrate southward to places with more available food.
CSeals, sea lions, and walruses migrate in the opposite direction to that of gray and humpback whales, so as to avoid competition for the food found in their favored coastal bays and lagoons
DBirds and bats that feed on monarch butterflies, including Mexican free-tailed bats, migrate along with the butterflies from eastern Canada and the United States to central Mexico.
EBirds like the dickcissel, junco, and several sparrows migrate to avoid predators that invade their territory during the winter months in search of prey
FBirds return north in the summer months to take advantage of favorable conditions for producing and raising young, and some sea animal migrations are also motivated by breeding concerns
