阅读第三十八篇：野生大象寿命更长

　　Longer Lives for Wild Elephants

　　Most people think of zoos as safe places for animals, where straggles such as difficulty finding food and avoiding predators don't exist. Without such problems, animals in zoos should live to a ripe old age1.

　　But that may not be true for2 the largest land animals on Earth. Scientists have known that elephants in zoos often suffer from poor health. They develop diseases. joint problems and behavior changes. Sometimes, they even become infertile, or unable to have babies。

　　To learn more about how captivity affects elephants, a team of international scientists compared the life spans of female elephants born in zoos with female elephants living outdoors in their native lands. Zoos keep detailed records of all the animals in their care, documenting factors such as birth dates, illnesses, weight and death. These records made it possible for the researchers to analyze 40 years of data on 800 African and Asian elephants in zoos across Europe. The scientists compared the life spans of the zoo-born elephants with the life spans of thousands of female wild elephants in Africa and Asian elephants that work in logging camps3, over approximately the same time period。

　　The team found that female African elephants born in zoos lived an average of 16.9 years. Their wild counterparts who died of natural causes lived an average of 56 years — more than three times as long. Female Asian elephants followed a similar pattern. In zoos, they lived 18.9 years, while those in the logging camps lived 41.7 years。

　　Scientists don't yet know why wild elephants seem to fare so much better than their zoo-raised counterparts. Georgia Mason, a biologist at the University of Guelph in Canada who led the study, thinks stress and obesity may be to blame4. Zoo elephants don't get the same kind of exercise they would in the wild, and most are very fat. Elephant social lives are also much different in zoos than in the wild. where they live in large herds and family groups。

　　Another finding from the study showed that Asian elephants born in zoos were more likely to die early than Asian elephants captured in the wild and brought to zoos. Mason suggests stress in the mothers in zoos might cause them to have babies that are less likely to survive。

　　The study raises some questions about acquiring more elephants to keep in zoos. While some threatened and endangered species living in zoos reproduce successfully and maintain healthy populations, that doesn't appear to be the case with elephants. "Currently, zoos are net consumers of elephants ,not net producers." Mason says。

　　练习：

　　1. According to the first two paragraphs, unlike other zoo animals, zoo elephants

　　A. have difficulty eating food。

　　B. live to a ripe old age。

　　C. are not afraid of predators。

　　D. develop health problems。

　　2. Which of the following about the international scientists' research on the life spans of elephants is NOT true? (See paragraph 3)？

　　A. They compared zoo elephants with wild elephants。

　　B. They kept detailed records of all the elephants in their care。

　　C. They analyzed the records of the elephants kept in zoos。

　　D. The zoo-born elephants they studied are kept in European zoos。

　　3. What do the scientist find in their research?

　　A. Female elephants live longer than male elephants。

　　B. Female zoo elephants live longer than their wild counterparts。

　　C. Female zoo elephants die much earlier than their wild counterparts。

　　D. Elephants in zoos and those in the wild enjoy the same long life spans。

　　4. What are the possible causes of stress and obesity Zoo-raised elephants generally suffer from?

　　A. They do not like living in herds。

　　B. They do not get enough exercise。

　　C. They do not live with their families。

　　D. Both B and C。

　　5. Which of the following does the author suggest in the last paragraph?

　　A. It may not be a wise policy to keep elephants in the zoo。

　　B. Elephants are no longer an endangered species。

　　C. Zoo-born elephants should be looked after more carefully。

　　D. Zoos should keep more animals except elephants。

　　译文：

　　人们通常认为动物园对于动物来说是安全的，因为他们没有猎食的困难，也不受其他肉食动物的威胁，所以动物园内的动物应该寿命较长。

　　但世界上最大的陆地动物却并非如此。科学家已经发现大象面临着很多健康问题，例如生病、关节问题和行为改变等，有时甚至会失去生育能力。

　　为了了解禁闭生活对大象的影响，一队国际科学家将在动物园出的雌象与生活在自然环境中的雌象的寿命进行了对比。动物园保留了所饲养动物的详细记录，包括出生日期、疾病、体重的死亡等因素。有了这些记录，研究人员能够分析全欧洲800头非洲象和非洲象历时40年的数据。科学家将动物园出生的大象与同一时间段的几千头非洲野生雌象、在伐木场劳动的亚洲象进行了寿命对比。

　　这些科学家发现，动物园出生的非洲雌象平均寿命是16.9年，而自然死亡的野生大象平均寿命是56年——是动物园大象的3倍多。亚洲雌象情况类似：动物园雌象寿命是18.9年，而伐木场雌象的寿命是41.7年。

　　科学家尚不清楚野生大象比动物园大象获得更好的原因。负责这一研究的加拿大圭尔夫大学生物学家乔治亚·梅森认为，压力和肥胖是问题的根源。动物园大象不像野生大象那样活动，因此非常肥胖。动物园大象的社会生活也很不同，不像野生大象那样过着群居的生活。

　　该研究的另一发现表明，在动物园出生的亚洲象比野外捕获后放入动物园的亚洲像死的要早。梅森认为动物园母象的压力可能导致小象成活率低。

　　对动物园大象的研究向人们提出了一个问题：是否应该将跟多的大象关进动物园。尽管有些濒危物种在动物园能够很好地繁衍生息、健康成长，大象却并非如此。梅森说，“动物园现在不是大象的纯粹生产者，二十纯粹消费者。”

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