ST_002系列托福综合写作

ST_002

综合写作

The toucan-a brightly marked bird of the tropics of the Americas --has long amazed people with its large, colorful bill. A third of the bird's entire length, the bill is longer than that of any other bird and is strikingly colored. Scientists have debated the question of why the toucan evolved such a bill. At least three theories have been proposed.

First. the toucan's bill is long and has sawlike edges, making it a potentially formidable weapon against predators. By jabbing with its bill, the toucan could deal a considerable blow to any animal trying to attack it. The sharp edges on the inside portion of its bill could also inflict damage if the toucan tried to fight off an enemy that had attacked it.

Second, the bill's shape and color could help the toucan hide in its tropical habitat by confusing potential predators. In the dim light of a dense tropical forest, a toucan's bill could easily be mistaken for a eaf or a piece of fruit. This illusion, in conjunction with the bird's brightly colored feathers that look like vegetation striped by shade and light, could provide truly effective camouflage protection.

Third, the toucan's bill could have evolved to help the bird coo itself by providing a large surface area through which excess heat can escape quickly. It is difficult for birds to lose heat through their bodies, since they are covered with insulating feathers. However, a toucan can effectively lose heat by pumping blood into its bill; from there the heat can easily radiate out. In a hot, tropical environment, it is important for birds to regulate their internal temperatures and prevent overheating.

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