ETS官方托福样题听力部分：生物课讲座

　　【ETS托福听力样题：a lecture in a biology class生物课讲座】ETS官方托福听力样题对托福备考阶段的考生具有非常重要的参考价值。通过样题可以迅速了解ETS的出题风格，和考试类型思路。

　　Narrator

　　Listen to part of a lecture in a biology class.

　　Professor

　　So today we’re gonna talk about song development in birds and how—you may be surprised to know—the songs of most songbird species are learned—not completely instinctual—which is what we used to think…so I’d like to start things off today by, um, centering our discussion on the chaffinch.

　　The chaffinch is a type of European songbird, and we’re gonna use the chaffinch’s song development as illustrative of songbirds’ song development in general, because many other songbirds follow this same pattern, this pattern of learning songs.

　　Okay, so soon after hatching, baby chaffinches start producing these, um, begging sounds, begging calls, actually, which basically are a message to the parents saying, “Feed me; feed me.” That’s all for about the first five weeks, until they grow feathers and start getting ready to fly, you know, become fledglings, and then those calls—those begging sounds—are replaced by, uh, well…you know how babies—human babies—you know how they make that…baby…babbling sound? Like little, soft, vocalized…murmurings? Well, that’s pretty much similar to the noises that fledgling chaffinches make at this next stage of development…which is called subsong…

　　“Subsong” makes sense, right, because “sub” means “below,” and so the subsong is…uh, below, or…happens before their mature song, right? It’s an immature, or underdeveloped song, a baby song. Make sense?

　　Okay, now, they’re not begging for food anymore with the subsong. So what do you figure they’re making these soft murmurings for? Well, it’s at this stage—what we call early subsong—that, and this is important, the chaffinch’s subsong begins to provide auditory feedback from which the chaffinch learns, and so...self-learning is taking place, because the fledgling hears itself calling out, hears the sounds it’s making, you know, hears, hears its subsong, and so, it’s kinda’ comparing it to the parent’s song and so self-learning is taking place, um, through this process…get it?…

　　Alright. Now, as the chaffinch gets a little older, it enters into what could be called late subsong where parts of its subsong start sounding more and more like its parent’s song,

　　and we have the next step in song development taking place in late subsong, that is, the introduction of plastic song within the subsong--plastic song referring to—I don’t have to write that on the board, do I?

　　—referring to the parts of the subsong that sound like the parent’s song.

　　Plastic song. Does that sound a little strange to you? Well, keep in mind that “plastic” has, um, formative implications, you know, it can mean, like, growth, or development into something

　　…like what the chaffinch’s song is doing…it’s developing into its parent’s song…it’s, uh, not quite fully realized yet—it doesn’t sound precisely like its parent’s song—remember this is still the subsong stage we’re talking about—but it’s on its way, the fledgling is still learning, imitating parts of its parent’s song, just not quite the whole thing yet.

　　So. The fledgling gets older and now it’s winter, and during the winter, the young chaffinch doesn’t practice its singing. But in the spring, the chaffinch starts back up again, singing and practicing, and this time there is more of an emergence of plastic song, ah…a stronger presence of it within the subsong, and so thereby, the parent’s song is growing increasingly more recognizable and distinct, follow? Then, after about a month, the young chaffinch’s song crystallizes into what’s called full song—the, um, exact song the adults sing. So full song’s, uh, a full-blown imitation of the adult song. Alright?

　　Now what’s interesting is that chaffinches are able to complete this process, even from only a short exposure to their parents’ song. Exposure during the first few weeks of life is really all they need, and after that they can remember it, even though they need quite a bit of practice to produce it accurately themselves. So the theory is that there is a sensitive period in the chaffinch’s early life, its early development, a special sensitive period during which it learns what its song should sound like. So chaffinches, um, along with many other birds, learn songs early in life, and when they become adults, they don’t change their songs—it’s a copy of the parents’ song, like we said, okay?

　　Narrator

　　Now get ready to answer the questions. You may use your notes to help you answer.

　　18. What aspect of a chaffinch’s song does the professor mainly discuss?

　　How it is used to beg for food

　　How it has changed over several generations

　　How its development differs from that of other songbirds

　　How it develops from an early age

　　19. What does the professor say about plastic song?

　　It imitates only parts of the parent’s song.

　　It is identical to subsong.

　　It is instinctual and does not need to be learned.

　　It represents the final stage in a chaffinch’s song development.

　　20. What is the evidence for chaffinches’ having a sensitive period for song learning?

　　They begin to practice their song in the spring.

　　They do not develop full song until their second year.

　　They need little exposure to adult song in order to learn it.

　　They do not make many sounds for the first five weeks of their lives.