新托福TPO17阅读原文(二)：Animal Signals in the Rain Forest
TPO17-2： Animal Signals in the Rain Forest
The daytime quality of light in forests varies with the density of the vegetation, the angle of the Sun, and the amount of cloud in the sky. Both animals and plants have different appearances in the various lighting conditions. A color or pattern that is relatively indistinct in one kind of light may be quite conspicuous in another.
In the varied and constantly changing light environment of the forest, an animal must be able to nd visual signals to members of its own species and at the same time avoid being detected by predators. An animal can hide from predators by choosing the light environment in which its pattern is least visible. This may require moving to different parts of the forest at different times of the day or under different weather conditions, or it may be achieved by changing color according to the changing light conditions. Many species of amphibians (frogs and toads) and reptiles (lizards and snakes) are able to change their color patterns to camouflage themlves. Some also signal by changing color. The cham
eleon lizard has the most striking ability to do this. Some chameleon species can change from a rather dull appearance to a full riot of carnival colors in conds. By this means, they signal their level of aggression or readiness to mate.
Other species take into account the changing conditions of light by performing their visual displays only when the light is favorable. A male bird of paradi may put himlf in the limelight by displaying his spectacular plumage in the best stage tting to attract a female. Certain butterflies move into spots of sunlight that have penetrated to the forest floor and display by opening and closing their beautifully patterned wings in the bright spotlights. They also compete with each other for the best spot of sunlight.
Very little light filters through the canopy of leaves and branches in a rain forest to reach ground level—or clo to the ground—and at tho levels the yellow-to-green wavelengths predominate. A signal might be most easily en if it is maximally bright. In the green-to-yellow lighting conditions of the lowest levels of the forest, yellow and green would be the brightest colors, but when an animal is signaling, the colors would not be
very visible if the animal was sitting in an area with a yellowish or greenish background. The best signal depends not only on its brightness but also on how well it contrasts with the background against which it must be en. In this part of the rain forest, therefore, red and orange are the best colors for signaling, and they are the colors ud in signals by the ground-walking Australian brush turkey. This species, which lives in the rain forests and scrublands of the east coast of Australia, has a brown-to-black plumage with bare, bright-red skin on the head and neck and a neck collar of orange-yellow looly hanging skin. During courtship and aggressive displays, the turkey enlarges its colored neck collar by inflating sacs in the neck region and then flings about a pendulous part of the colored signaling apparatus as it utters calls designed to attract or repel. This impressive display is clearly visible in the light spectrum illuminating the forest floor.
Less colorful birds and animals that inhabit the rain forest tend to rely on other forms of signaling other than the visual, particularly over long distances. The piercing cries of the rhinoceros hornbill characterize the Southeast Asian rain forest, as do the unmistakable calls of the gibbons. In denly wooded environments, sound is the best means of comm
unication over distance becau in comparison with light, it travels with little impediment from trees and other vegetation. In forests, visual signals can be en only at short distances, where they are not obstructed by trees. The male riflebird exploits both of the modes of signaling simultaneously in his courtship display. The sounds made as each wing is opened carry extremely well over distance and adverti his prence widely. The ritualized visual display communicates in clo quarters when a female has approached.
TPO17-2译文：雨林中的动物信号
森林中白天的光照质量随着植被密度、太阳角度以及天空中云的数量的变化而变化。在不同的光照条件下，动植物会有不同的表现。在某种光照下相对较难辨认的颜色或式样，在另外一种光照下也许会变得相当显眼。
在多样和不断变化的森林光照环境下，动物必须能够发送视觉信号给自己的同类，同时避免被捕食者发现。动物可以选择最不易看得见的光照环境来躲避捕食者的视线。这就要求动物能在白天不同的时间或者在不同的天气条件下移动到森林的不同方位，或者，它们也
可以根据不同的光照来改变自身的颜色。很多两栖动物(青蛙和蟾蜍)和爬行动物(蜥蜴和蛇)都可以通过改变颜色图案来伪装自己。有些动物还通过改变颜色来发出信号。变色龙在这方面有着最惊人的能力。有些变色龙物种可以在几秒钟之内就把暗淡的外表变得灿烂夺目。通过这种方式，它们可以传达出攻击程度和交配意愿。
其他的物种则只有在光照对它们有利的时候才会利用光照，来进行视觉上的自我展现。雄性极乐鸟会置身于汇聚的光线之下，在最佳的场景中展现自己缤纷绚烂的羽翼，以吸引雌鸟的注意。某些蝴蝶则飞到穿透森林的太阳光点处，，在明亮的光点中扇动着带有美丽图案的翅膀来展现自己。它们还会互相争夺最佳的光照位置。
很少有光能够穿透热带雨林的树冠层到达地平面——或是接近地面——而能达到底部的主要是黄绿光波。如果是色彩极为明亮的信号，可能更容易被看见。在森林底层的黄绿光照条件下，黄色和绿色是最明亮的颜色，但是当动物发送信号时，如果处于浅黄或浅绿的背景下，这些颜色就不容易看到了。最佳的信号不仅取决于其明亮度，还在于它与背景颜色的对比度。因此，在热带雨林这块区域，红色和橙色是最佳的信号颜色，而这也是地面行走的澳大利亚灌丛火鸡最善于使用的信号颜色。这个物种生活在澳大利亚东海岸的雨林和
灌木丛中，长着黑棕色的羽毛，有着光秃秃、亮红色的头和脖子，颈圈上是一层橙黄色的松垮垮的皮。在求爱期和发起进攻时，火鸡通过给颈部液囊充气扩张颈圈，晃动着下垂的鲜艳的信号装置，随之发出叫声来吸引异性或击退敌人。在照亮雨林底层的光谱环境下，能够清晰地看到这种让人印象深刻的展示。
