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题目材料：
The following passage comes from a study of gull bill markings.
Some species of gulls have uniformly colored bills, but many (62 percent in our sample) have beaks with differently colored tips, stripes, or spots that act as a focus for the pecking of newly hatched chicks as they beg for food. In an attempt to understand why, we determined whether adult gulls of those species with newly hatched chicks that are small in relation to the size of the adult are more likely to have such patterned beaks. This work is based on Hailman' s (1967) suggestion that gulls with greater bill depths (large species) tend to have only a restricted area of red on the bill (i.e., a red tip or spot), whereas smaller-billed species have uniform bills. We suggest that the most plausible reason for any size-related difference is that concentrating a small chick's pecking on a particular part of the bill is more effective than is unfocused pecking in stimulating the adult to regurgitate food. As well as encouraging the chick to peck, the tip of the bill, or the gonys (where stripes and spots are located), might be more sensitive than are other parts of the beak to the feeble pecking of a small chick, or a small chick might more effectively occupy the parent's visual field when
pecking there.
以上解析由 考满分老师提供。
