那利亚纳乌鸦可能在75年内灭绝
文章来源:未知 文章作者:meng 发布时间:2010-12-21 03:43 字体: [ ]  进入论坛
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Researchers from the University of Washington say the Mariana crow(乌鸦) , a forest crow living on Rota Island in the western Pacific Ocean, will go extinct in 75 years. The extinction1 could happen almost twice as soon as previously2 believed.

The crow's extinction can be prevented with a bird management program that focuses on helping3 fledgling(羽毛刚丰的) birds reach their first birthday, said James Ha, UW research associate professor in psychology4.

Ha examined survival rates in 97 Mariana crows – Corvus kubaryi – that had been tracked between 1990 and 2010 by researchers. He found that 40 percent of fledgling crows made it to their first birthday.

The rapid decline of young birds is twice what researchers previously estimated.

"It's the first year of survival that's the most crucial," said Ha, lead author of a report on the research. "If only 40 percent of fledglings survive their first year, then we predict the species will go extinct in 75 years."

Ha and his co-authors published the report in the current issue of Bird Conservation International.

The 75-year extinction estimate is according to a population model that factors in the estimated number of existing Mariana crows – 330 – with the 40 percent first-year survival rate, average number of fledglings per nest and fertility of female birds. Using this model, Ha found that 91 birds would exist in 20 years and that in 75 years the species would be extinct.

Previously, biologists believed that the first-year survival rate of Mariana crows was higher, around 60 to 80 percent.

When Ha used those estimates in his population model, the outlook was not as grim for the birds. At 60 percent first-year survival rate, Mariana crows would dwindle5 to(减少到) 218 birds in 20 years and become extinct in 133 years. And an 80 percent first-year survival rate projects that in 20 years there would be 453 birds, a growing population that would avoid extinction.

"According to the population model, if we can boost fledgling survival from 40 percent to 70 percent, the Mariana crows will be fine," Ha said.

Of the about 35 crow species, Mariana crows are considered rare and classified as critically endangered. Weighing about a half of a pound, Mariana crows are 40 percent smaller than other crows, such as the Northwest crow.

Monogamously-mating, Mariana crows live exclusively on Rota Island, populated by about 1,200 people and located 56 miles northeast of Guam. Rota is a U.S. territory and is up for consideration as a U.S. national park.

Ha and Renee Ha, co-author of the report and UW research scientist in psychology, fear that Rota faces the same avian demise6 as Guam, which has no forest birds.

Brown tree snakes introduced to the island after World War II wiped out native birds, such as the Guam flycatcher and the Rufous fantail.

The Has suspect that the uncontrolled increase of feral cats on Rota is leading to the decrease of Mariana crows, much like brown tree snakes led to the disappearance7 of forest birds on Guam.

The researchers say that a captive rearing program could save the Mariana crows. They hope to set up a rearing facility where they could incubate(孵化,培育) eggs from the wild, raise the fledglings until their first birthday and then release the grown birds into nesting sites on the island.



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1 extinction sPwzP     
n.熄灭,消亡,消灭,灭绝,绝种
参考例句:
  • The plant is now in danger of extinction.这种植物现在有绝种的危险。
  • The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。
2 previously bkzzzC     
adv.以前,先前(地)
参考例句:
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
3 helping 2rGzDc     
n.食物的一份&adj.帮助人的,辅助的
参考例句:
  • The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
  • By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。
4 psychology U0Wze     
n.心理,心理学,心理状态
参考例句:
  • She has a background in child psychology.她受过儿童心理学的教育。
  • He studied philosophy and psychology at Cambridge.他在剑桥大学学习哲学和心理学。
5 dwindle skxzI     
v.逐渐变小(或减少)
参考例句:
  • The factory's workforce has dwindled from over 4,000 to a few hundred.工厂雇员总数已经从4,000多人减少到几百人。
  • He is struggling to come to terms with his dwindling authority.他正努力适应自己权力被削弱这一局面。
6 demise Cmazg     
n.死亡;v.让渡,遗赠,转让
参考例句:
  • He praised the union's aims but predicted its early demise.他赞扬协会的目标,但预期这一协会很快会消亡。
  • The war brought about the industry's sudden demise.战争道致这个行业就这么突然垮了。
7 disappearance ouEx5     
n.消失,消散,失踪
参考例句:
  • He was hard put to it to explain her disappearance.他难以说明她为什么不见了。
  • Her disappearance gave rise to the wildest rumours.她失踪一事引起了各种流言蜚语。
TAG标签: birds extinction crow
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