READING COMPREHENSION
Birds that feed in flocks commonly retire together into roosts. The reasons for roosting communally are not always obvious, but there are some likely benefits. In winter especially, it is important for birds to keep warm at night and conserve precious food reserves. One way to do this is to find a sheltered roost. Solitary roosters shelter in dense vegetation or enter a cavity - horned larks dig holes in the ground and ptarmigan burrow into snow banks - but the effect of sheltering is magnified by several birds huddling together in the roosts, as wrens, swifts, brown creepers, bluebirds, and anis do. Body contact reduces the surface area exposed to the cold air, so the birds keep each other warm. Two kinglets huddling together were found to reduce their heat losses by a quarter and three together saved a third of their heat.
The second possible benefit of communal roosts is that they act as "information centers." During the day, parties of birds will have spread out to forage over a very large area. When they return in the evening some will have fed well, but others may have found little to eat. Some investigators have observed that when the birds set out again next morning, those birds that did not feed well on the previous day appear to follow those that did. The behavior of common and lesser kestrels may illustrate different feeding behaviors of similar birds with different roosting habits. The common kestrel hunts vertebrate animals in a small, familiar hunting ground, whereas the very similar lesser kestrel feeds on insects over a large area. The common kestrel roosts and hunts alone, but the lesser kestrel roosts and hunts in flocks, possibly so one bird can learn from others where to find insect swarms.
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Finally, there is safety in numbers at communal roosts since there will always be a few birds awake at any given moment to give the alarm. But this increased protection is partially counteracted by the fact that mass roosts attract predators and are especially vulnerable if they are on the ground. Even those in trees can be attacked by birds of prey. The birds on the edge are at greatest risk since predators find it easier to catch small birds perching at the margins of the roost.
31. What does the passage mainly discuss?
(A) How birds find and store food.
(B) How birds maintain body heat in the winter.
(C) Why birds need to establish territory.
(D) Why some species of birds nest together.
32. The word "conserve" is closest in meaning to
(A) retain
(B) watch
33. Ptarmigan keep warm in the winter by
(A) huddling together on the ground with other birds.
(B) Building nests in trees.
(C) Burrowing into dense patches of vegetation
(D) Digging tunnels into the snow.
34. The word "magnified" in line 6 is closest in meaning to
(A) caused
(B) modified
(C) locate
(D) share
(C) intensified
(D) combined
(C) Nest together for warmth
35. The author mentions kinglets as an example of birds that
(A) protect themselves by nesting in holes.
(B) Nest with other species of birds
(D) Usually feed and nest in pairs
36. Which of the following statements about lesser and common kestrels is true?
(A) The lesser kestrel and the common kestrel have similar diets. (B) The lesser kestrel feeds sociably but the common kestrel does not.
(C) The common kestrel nests in larger flocks than does the lesser kestrel.
(D) The common kestrel nests in trees, the lesser kestrel nests on the ground.
37. The word "counteracted" is closest in meaning to
(A) suggested
(B) negated
(C) measured
(D) shielded
38. Which of the following is NOT mentioned in the passage as an advantage derived by birds that huddle together while sleeping?
(A) Some members of the flock warm others of impending dangers. (B) Staying together provides a greater amount of heat for the whole flock.
(C) Some birds in the flock function as information centers for others who are looking for food.
(D) Several members of the flock care for the young.
39. Which of the following is a disadvantage of communal roosts that is mentioned in the passage?
(A) Diseases easily spread among the birds.
(B) Groups are more attractive to predators than individual birds.
(C) Food supplies are quickly depleted
(D) Some birds in the group will attack the others.
40. The word "they" refers to
(A) a few birds
(B) mass roosts
(C) predators
(D) trees