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托福阅读TPO11(试题+答案+译文)第3篇:Begging by Nestlings
托福阅读原文
Many signals that animals make em to impo on the signalers costs that are overly damaging. A classic example is noisy begging by nestling songbirds when a parent returns to the nest with food. The loud cheeps and peeps might give the location of the nest away to a listening hawk or raccoon, r
esulting in the death of the defenless nestlings. In fact, when tapes of begging tree swallows were played at an artificial swallow nest containing an egg, the egg in that “noisy” nest was taken or destroyed by predators before the egg in a nearby quiet nest in 29 of 37 trials.朋友圈评论
Further evidence for the costs of begging comes from a study of differences in the begging calls of warbler species that nest on the ground versus tho that nest in the relative safety of trees. The young of ground-nesting warblers produce begging cheeps of higher frequencies than do their tree-nesting relatives. The higher-frequency sounds do not travel as far, and so may better conceal the individuals producing them, who are especially vulnerable to predators in their ground nests. David Haskell created artificial nests with clay eggs and placed them on the ground beside a tape recorder that played the begging calls of either
tree-nesting or of ground-nesting warblers. The eggs “advertid” by the tree-nesters' begging calls were found bitten significantly more often than the eggs associated with the ground-nesters' calls.
The hypothesis that begging calls have evolved properties that reduce their potential for attracting predators yields a prediction: baby birds of species that experience high rates of nest predation should produce softer begging signals of higher frequency than nestlings of other species less often
victimized by nest predators. This prediction was supported by data collected in one survey of 24 species from an Arizona forest, more evidence that predator pressure favors the evolution of begging calls that are hard to detect and pinpoint.
Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where veral other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds.
If parent birds u begging intensity to direct food to healthy offspring capable of vigorous begging, then parents should make food delivery decisions on the basis of their offsprings’ c alls. Indeed, if you take baby tree swallows out of a nest for an hour feeding half the t and starving the other half, when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than tho who beg less vigorously.
党支部年终总结As the experiments show, begging apparently provides a signal of need that parents u to make judgments about which offspring can benefit most from a feeding. But the question aris, why don't nestlings beg loudly when they aren't all that hungry? By doing so, they could possibly cure more food, which should result in more rapid growth or larger size, either of which is advantageous. The answer lies apparently not in the incread energy costs of exaggerated begging—such energy costs are small relative to the potential gain in calories—but rather in the damage that any successful cheater would do to its siblings, which share genes with one another. An individual's success in propagating his or her genes can be affected by more than just his or her own personal reproductive success. Becau clo relatives have many of the same genes, animals that harm their clo relatives may in effect be destroying some of their own genes. Therefore, a begging nestling that cures food at the expen of its siblings might actually leave behind fewer copies of its
genes overall than it might otherwi.
女性私处按摩托福阅读试题
1.The phra “impo on” in the passage(Paragraph 1)is clost in meaning to
森林的英语
文言文名句A.increa for
B. remove from
C.place on
字组词
D.distribute to
2.According to paragraph 1, the experiment with tapes of begging tree swallows establishes which of the following?
A.Begging by nestling birds can attract the attention of predators to the nest.
B.Nest predators attack nests that contain nestlings more frequently than they attack nests that contain only eggs.
C.Tapes of begging nestlings attract predators to the nest less frequently than real begging calls do.
D.Nest predators have no other means of locating bird nests except the begging calls of nestling birds.
excel求差
初春时节3.The word “artificial”(Paragraph 2)in the passage is clost in meaning to
