英語(yǔ)聽(tīng)力文摘 鳥(niǎo)兒捕蟲(chóng)的法寶
鳥(niǎo)兒捕蟲(chóng)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(niǎo)跳來(lái)跳去，注視著草叢，晃頭晃腦地搜尋著可口多汁的昆蟲(chóng)。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(chóng)兒飛走了。
尋找獵物的線索
通常鳥(niǎo)兒們是通過(guò)視覺(jué)、聽(tīng)覺(jué)，有時(shí)可能是觸覺(jué)(昆蟲(chóng)的振動(dòng))這些線索來(lái)尋找獵物，其中視覺(jué)居多。
從知更鳥(niǎo)晃頭晃腦地尋找食物可以推斷出視覺(jué)和聽(tīng)覺(jué)線索的利用，但是直到科學(xué)家們?cè)趯?shí)驗(yàn)室中測(cè)試，我們才真正明確知更鳥(niǎo)如何發(fā)現(xiàn)昆蟲(chóng)。
測(cè)試?guó)B兒
在大型鳥(niǎo)舍中，給鳥(niǎo)兒們提供面粉蟲(chóng)藏在泥里的托盤(pán)。
為了測(cè)試?guó)B兒是否通過(guò)嗅覺(jué)尋找獵物，托盤(pán)里分別藏有活著的昆蟲(chóng)和死了的昆蟲(chóng)。知更鳥(niǎo)找出的多是活著的昆蟲(chóng)，這說(shuō)明知更鳥(niǎo)尋找獵物時(shí)并沒(méi)有利用嗅覺(jué)。
下一個(gè)測(cè)試是：把托盤(pán)懸掛起來(lái)，這樣知更鳥(niǎo)的腳碰不到泥土，也不能探測(cè)昆蟲(chóng)的振動(dòng)。測(cè)試并沒(méi)有影響知更鳥(niǎo)捕捉昆蟲(chóng)，這說(shuō)明知更鳥(niǎo)尋找獵物時(shí)并沒(méi)有利用觸覺(jué)。
聲音線索
用紙板作為障礙物破壞視覺(jué)線索，鳥(niǎo)兒依然能找到昆蟲(chóng)。說(shuō)明鳥(niǎo)兒是用另種線索。最后的實(shí)驗(yàn)利用白色噪音破壞聲音線索，鳥(niǎo)兒尋找昆蟲(chóng)困難起來(lái)了。
研究結(jié)果是知更鳥(niǎo)可以利用視覺(jué)或聽(tīng)覺(jué)中任一線索尋找泥土中的昆蟲(chóng)，但是也很可能是兩種皆有。所以，下次你再看見(jiàn)知更鳥(niǎo)在草叢中搖頭晃腦的，你可以確定它們是通過(guò)聽(tīng)覺(jué)尋找垂涎的美味了!
