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?
黑頭鶯是一種體型較小的鳥類，主要生活在歐洲中部。50年前，大多數(shù)黑頭鶯每到冬季就會(huì)遷徙到南部的西班牙或者葡萄牙。但是自20世紀(jì)60年代起，越來越多的黑頭鶯開始飛往英國和愛爾蘭過冬。到2003年，有三分之一的英國家庭后院里的喂食器上出現(xiàn)過黑頭鶯。然而是什么促使如此多的黑頭鶯另擇越冬地呢？
The direction birds migrate is coded in their genes. 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 pointed them in a slightly different direction and they ended up in Britain.
鳥類遷徙的方向由基因決定。每個(gè)鳥群遷徙時(shí)都有個(gè)平均方向，但個(gè)體可以在偏離這個(gè)方向40度范圍內(nèi)活動(dòng)。盡管歷史上黑頭鶯遷徙的平均方向是朝著葡萄牙，但還是有不少黑頭鶯定位稍有偏差，結(jié)果就來到了英國。
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.
在英國過冬的黑頭鶯數(shù)量激增，至于它們選擇飛往北方而不是南方，其中肯定有一些顯著的優(yōu)勢。也許是因?yàn)橛容^近，不必大費(fèi)周折飛那么遠(yuǎn)，也許是因?yàn)橛性S多鳥類愛好者，在后院到處懸掛喂食器。
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.
但來自德國和英國的研究人員認(rèn)為關(guān)鍵區(qū)別在于英國冬季的白晝較短。白晝短這一點(diǎn)可以影響到鳥類的遷移和繁殖行為，所以，在英國過冬的鳥類會(huì)比飛往南方的鳥類提前十天返回夏日的繁殖場所。
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 disposition to fly to Britain steadily increases.
開頭的十天會(huì)保證這些候鳥們占領(lǐng)最好的領(lǐng)地，迅速開始孕育下一代。并且，與在南方配對(duì)的雌鳥相比，與英國的雄鳥配對(duì)的雌鳥產(chǎn)蛋更多，孵出的雛鳥也更多。年復(fù)一年，黑頭鶯會(huì)把向英國遷徙的基因一代代傳下去。因此，飛往英國過冬的黑頭鶯數(shù)量急劇增長。
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