英語聽力文摘 鳥兒捕蟲的法寶
鳥兒捕蟲的線索
Everyone is familiar with the sight of robins hopping around the yard, peering into the grass or “head-cocking” to locate a nice juicy worm. In no time, they find their prey and fly off with a mouthful.
Cues to find prey
Birds are known to use visual, auditory, and possibly vibrations or tactile cues to find prey, but vision is predominant.
The way the robins turn their head when searching for food suggests they could be using visual or auditory cues, but it wasn’t until scientists tested robins in the lab that we really knew for sure how they find worms.
Testing the birds
Birds were placed in aviaries where they could be given buried mealworms in trays of dirt.
To test if they were using scent to locate their prey, birds were offered trays with buried live, moving worms and dead ones. Robins found the live worms more often, suggesting they were not using scent.
In the next test, they were given hanging food trays to keep them from touching the soil with their feet and detecting the worm’s vibrations. The trays did not affect their ability to find the worms, suggesting they do not use tactile cues.
Sound Cues
When cardboard was used as a barrier to block visual cues, the birds could still find the worms. That meant they were using another sense. A last experiment used white noise to block sound cues and the birds had more difficulty finding the worms.
The research concluded that robins could use either visual or auditory cues alone to find worms in the soil, but probably use both. So the next time you see a robin “head-cocking” you can be fairly sure it’s listening and looking for those mouthwatering treats!
后院里，知更鳥跳來跳去，注視著草叢，晃頭晃腦地搜尋著可口多汁的昆蟲。這樣的情景相信大家都不陌生。一旦發(fā)現(xiàn)“獵物”，它馬上叼著蟲兒飛走了。
尋找獵物的線索
通常鳥兒們是通過視覺、聽覺，有時可能是觸覺(昆蟲的振動)這些線索來尋找獵物，其中視覺居多。
從知更鳥晃頭晃腦地尋找食物可以推斷出視覺和聽覺線索的利用，但是直到科學家們在實驗室中測試，我們才真正明確知更鳥如何發(fā)現(xiàn)昆蟲。
測試鳥兒
在大型鳥舍中，給鳥兒們提供面粉蟲藏在泥里的托盤。
為了測試鳥兒是否通過嗅覺尋找獵物，托盤里分別藏有活著的昆蟲和死了的昆蟲。知更鳥找出的多是活著的昆蟲，這說明知更鳥尋找獵物時并沒有利用嗅覺。
下一個測試是：把托盤懸掛起來，這樣知更鳥的腳碰不到泥土，也不能探測昆蟲的振動。測試并沒有影響知更鳥捕捉昆蟲，這說明知更鳥尋找獵物時并沒有利用觸覺。
聲音線索
用紙板作為障礙物破壞視覺線索，鳥兒依然能找到昆蟲。說明鳥兒是用另種線索。最后的實驗利用白色噪音破壞聲音線索，鳥兒尋找昆蟲困難起來了。
研究結(jié)果是知更鳥可以利用視覺或聽覺中任一線索尋找泥土中的昆蟲，但是也很可能是兩種皆有。所以，下次你再看見知更鳥在草叢中搖頭晃腦的，你可以確定它們是通過聽覺尋找垂涎的美味了!
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