ployed by
ground-nesting
birds involve plovers, small birds that typically nest on beaches or in open
fields, their
nests merely scrapes in the sand or earth. Plovers also have an effective
repertoire of tricks
Line for distracting potential nest predators from their exposed and
defenseless eggs or chicks.
(5) The ever-watchful plover can detect a possible threat at a considerable
distance. When
she does, the nesting bird moves inconspicuously off the nest to a spot well
away from
eggs or chicks. At this point she may use one of several ploys. One technique
involves
first moving quietly toward an approaching animal and then setting off noisily
through
the grass or brush in a low, crouching run away from the nest, while emitting
rodent like
(10) squeaks. The effect mimics a scurrying mouse or vole, and the behavior
rivets the
attention of the type of predators that would also be interested in eggs and
chicks.
Another deception begins with quiet movement to an exposed and visible location
well
away from the nest. Once there, the bird pretends to incubate a brood. When the
predator
approaches, the parent flees, leaving the false nest to be searched. The
direction in which
(15) the plover "escapes" is such that if the predator chooses to
follow, it will be led still further
away from the true nest.
The plover's most famous stratagem is the broken-wing display, actually a
continuum
of injury-mimicking behaviors spanning the range from slight disability to
near-complete
helplessness. One or both wings are held in an abnormal position, suggesting
injury. The
(20) bird appears to be attempting escape along an irregular route that
indicates panic. In the
most extreme version of the display, the bird flaps one wing in an apparent
attempt to
take to the air, flops over helplessly, struggles back to its feet, runs away a
short distance,
seemingly attempts once more to take off, flops over again as the
"useless" wing fails to
provide any lift, and so on. Few predators fail to pursue such obviously
vulnerable prey.
Needless to say, each short run between "flight attempts" is directed
away from the nest.
10. What does the passage mainly discuss?
(A) The nest-building techniques of plovers
(B) How predators search for plovers
(C) The stra
上一页 [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] ... 下一页 >>
