时差N小时 黑头莺为何改变迁徙模式?

Blackcaps are small songbirds that breed in Central Europe. Fifty years ago, most blackcaps went south for the winter to Spain or Portugal. But since the 1960s more and more blackcaps have started wintering in Britain and Ireland. By 2003, blackcaps were seen perched at one in every three backyard bird feeders in Britain! But why did so many blackcaps change their winter vacation location?

黑头莺是一种体型较小的鸟类，主要生活在欧洲中部。50年前，大多数黑头莺每到冬季就会迁徙到南部的西班牙或者葡萄牙。但是自20世纪60年代起，越来越多的黑头莺开始飞往英国和爱尔兰过冬。到2003年，有三分之一的英国家庭后院里的喂食器上出现过黑头莺。然而是什么促使如此多的黑头莺另择越冬地呢？

The direction birds migrate is coded in their genes¹. Each population of birds has an average direction they will go, but individuals can vary as much as forty degrees from the average. Although historically, the average direction for blackcaps was towards Portugal, a few birds' genes pointed² them in a slightly different direction and they ended up in Britain.

鸟类迁徙的方向由基因决定。每个鸟群迁徙时都有个平均方向，但个体可以在偏离这个方向40度范围内活动。尽管历史上黑头莺迁徙的平均方向是朝着葡萄牙，但还是有不少黑头莺定位稍有偏差，结果就来到了英国。

But for the numbers of blackcaps wintering in Britain to change so dramatically, there must be some significant advantage to fly north rather than south. Perhaps the benefit is simply from the shorter, less taxing flight to Britain. Or maybe it’s because Britain has many bird lovers that stock backyard birdfeeders.

在英国过冬的黑头莺数量激增，至于它们选择飞往北方而不是南方，其中肯定有一些显著的优势。也许是因为英国比较近，不必大费周折飞那么远，也许是因为英国有许多鸟类爱好者，在后院到处悬挂喂食器。

But researchers from Germany and the UK believe the key difference is the shorter winter days in Britain. Shorter days affect migration³ and breeding behavior, so British birds return to summer breeding grounds about ten days earlier than birds that went south.

但来自德国和英国的研究人员认为关键区别在于英国冬季的白昼较短。白昼短这一点可以影响到鸟类的迁移和繁殖行为，所以，在英国过冬的鸟类会比飞往南方的鸟类提前十天返回夏日的繁殖场所。

This ten-day head start lets British migrants claim the best territories and start breeding sooner. Females paired with British males laid more eggs and hatched more chicks than those mated to southern birds. Each year, blackcaps with genes orienting them towards Britain pass on those genes to more chicks. And so the number of blackcaps with the disposition⁴ to fly to Britain steadily⁵ increases.

开头的十天会保证这些候鸟们占领最好的领地，迅速开始孕育下一代。并且，与在南方配对的雌鸟相比，与英国的雄鸟配对的雌鸟产蛋更多，孵出的雏鸟也更多。年复一年，黑头莺会把向英国迁徙的基因一代代传下去。因此，飞往英国过冬的黑头莺数量急剧增长。

1 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

2 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

3 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

4 disposition   

n.性情，性格；意向，倾向；排列，部署

参考例句：

• He has made a good disposition of his property.他已对财产作了妥善处理。
• He has a cheerful disposition.他性情开朗。

5 steadily   

adv.稳定地；不变地；持续地

参考例句：

• The scope of man's use of natural resources will steadily grow.人类利用自然资源的广度将日益扩大。
• Our educational reform was steadily led onto the correct path.我们的教学改革慢慢上轨道了。