【英语时差8,16】改变了迁移模式的黑头莺

Blackcaps Change Their Migration¹ Patterns…But Why? 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? The direction birds migrate is coded in their genes². 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 pointed³ them in a slightly different direction and they ended up in Britain. 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. But researchers from Germany and the UK believe the key difference is the shorter winter days in Britain. Shorter days affect migration and breeding behavior, so British birds return to summer breeding grounds about ten days earlier than birds that went south. 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.

1 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。

2 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

3 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。

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。