TPO11閱讀 Begging by Nestlings - 英檢

我想請問第14題整合題，我是選ABC，但考滿分給的答案是ACD，但我在小馬托福看到的詳解給的是ABC@@ 詳解有給跟沒給差不多QQ
我自己的想法是:B是根據第四段選出來的，但在作答時也覺得D也應該選(根據第一段)，相較之下B應該比D合適

想請問B還是D更符合這題整合題的答案?因為看到兩種不同版本的答案，又一直想不透
謝謝><

附上原文
Many signals that animals make seem to impose 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. These loud cheeps and peeps
might give the location of the nest away to a listening hawk or raccoon,
resulting in the death of the defenseless 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.

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 those
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. These 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 “advertised” 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
several 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 use 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’ calls. Indeed, if you take baby tree
swallows out of a nest for an hour feeding half the set 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 those who beg less vigorously.

As these experiments show, begging apparently provides a signal of need that
parents use to make judgments about which offspring can benefit most from a
feeding. But the question arises, why don't nestlings beg loudly when they
aren't all that hungry? By doing so, they could possibly secure more food,
which should result in more rapid growth or larger size, either of which is
advantageous. The answer lies apparently not in the increased 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. Because close relatives have many
of the same genes, animals that harm their close relatives may in effect be
destroying some of their own genes. Therefore, a begging nestling that
secures food at the expense of its siblings might actually leave behind fewer
copies of its genes overall than it might otherwise.

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