2017年11月18日托福阅读真题+题目+答案：Birds and Food Shortage

2017年11月18日托福阅读真题+题目+答案：Birds and Food Shortage

The term“food shortage"has been used for food that is inadequate in quantity,quality,or availability.Whatever the abundance of food in the environment,if it is for some reason unavailable,bird species in either inland or coastal areas may starve. Food sources like intertidal invertebrates retreat deeper in the mud in cold weather,putting them beyond the reach of shorebirds,while many soil-dwelling invertebrates move deeper into the ground during drought.Such behaviors illustrate the general points that only a proportion of potential food items may be accessible to birds at any one time,and that this proportion may change through time in response to other conditions.Secondly,if food is plentiful but of low nutrient content or digestibility,a bird may be unable to process enough each day to maintain its weight.This is particularly true of herbivores (plant eaters)eating fibrous,or coarse,vegetation,and food shortage may arise partly from the structure of a bird's inner parts,or gut,which limits the rate at which food can be processed.In general among birds,species differences in gut structure correspond with dietary differences,and in species whose diet changes seasonally,gut structure may change accordingly.The need for change in gut structure can make some species vulnerable at times of rapid shift in diet,as when snowfall forces birds suddenly from one food type to another.

1.What can be inferred about birds that experience a"rapid shift in diet"?

A Their gut structure may not immediately adapt to the new food source.

B They store body fat at the wintering or migratory grounds for later use when they breed.

C They require a variety of new foods to maintain a healthy gut structure.

D They are able to process food without changing their gut structure.

2.According to paragraph 1,why do some shorebirds experience food shortages in cold weather?

A Food sources are no longer available because they decrease in number.

B The mud in which food sources such as intertidal invertebrates live hardens,making the food source less available.

C Food sources move to a location that is not accessible to shorebirds.

D Food sources such as intertidal invertebrates become more difficult to digest.

Many bird species cushion the effects of food shortage by storage, either of body fat or of food itself ⬛ .In small birds,fat stores are accumulated mainly for use overnight,and few species can last more than a day or two without feeding. ⬛ Larger birds,with their relatively lower metabolic (energy)demands,can store relatively more energy per unit of body weight. ⬛ As a result,larger birds can rely on internal reserves for longer than small ones,more than two weeks in large waterfowl. ⬛ Many birds store some body fat and protein in preparation for breeding,extreme examples being Arctic-nesting geese,in which the females produce and incubate their eggs almost entirely on reserves accumulated in wintering or migration areas.For some weeks,then,they are protected against the need to feed on their breeding grounds.Most migratory birds accumulate body fat for the journey,the amount depending on the duration of unbroken flight.

3.According to the author,how do"Arctic-nesting geese"protect themselves from food shortage?

A They breed in their wintering or migration grounds to save energy.

B They store body fat at the wintering or migratory grounds for later use when they breed.

C They have a short breeding and incubation period so as not to use up all their stored energy.

D They store food in their breeding ground before wintering or migrating elsewhere.

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