托福og3听力What does the professor mainly discuss? 答案解析

[00:00.00]Listen to part of a lecture in an environmental science class.
[00:04.78]Professor: Now, we’ve been talking about the loss of animal habitat from housing developments, um， growing cities . . . small habitat losses.
[00:15.05]But today I want to begin talking about what happens when habitat is reduced across a large area.
[00:21.62]There are, of course, animal species that require large areas of habitat... and, um, some migrate over very long distances. [00:31.63]So what’s the impact of habitat loss on those animals?Animals that need large areas of habitat?
[00:38.84]Well, I’ll use the hummingbirds as an example. [00:42.68]Now, you know a hummingbird is amazingly small. [00:46.32]But even though it’s really tiny, it migrates over very long distances ...travels up and down the Western Hemisphere ... the Americas . . . back and forth between where it breeds in the summer and the warmer climates where it spends the winter. [01:00.96]So we would say that this whole area over which it migrates is its habitat because on this long-distance journey, it needs to come down to feed and sleep every so often, right?
[01:13.51]Well，the hummingbird beats its wings-get this-about 3,000 times per minute. [01:21.21]So you think, wow, it must need a lot of energy, a lot of food, right?[01:25.66]Well, it does-it drinks a lot of nectar from flowers and feeds on some insects-but it's energy-efficient, too. [01:33.87]You can't say it isn’t. [01:35.49]I mean as it flies all the way across the Gulf of Mexico, it uses up almost none of its body fat. [01:41.66]But that doesn't mean it doesn't need to eat! [01:44.45]So hummingbirds have to rely on plants in their natural habitat. [01:49.69]And it goes without saying, but... well, the opposite is true as well. [01:54.64]Plants depend on hummingbirds too. [01:57.03]There are some flowers that can only be pollinated by the hummingbird. [02:01.12]Without it stopping to feed and spreading pollen from flower to flower, these plants would cease to exist!
[02:08.76]But the problem, well... as natural habitat along these migration routes is developed by humans for housing or agriculture, or, um, cleared for raising cattle, for instance ... there’s less food available for migrating hummingbirds. [02:26.35]Their nesting sites are affected, too ... the same ... by the same sorts of human activities. [02:31.97]And all of these activities pose a real threat to the hummingbird population.
[02:37.34]So, to help them survive, we need to preserve their habitats ... And one of the concrete ways people have been doing this is by cleaning up polluted habitat areas and then replanting flowers, uh, replanting native flowers that hummingbirds feed on.
[02:55.45]Promoting ecological tourism is another way to help save their habitat. [03:00.97]As the number of visitors-ecotourists who come to hummingbird habitats to watch the birds-the more the number of visitors grows, the more local businesses profit. [03:11.88]So ecological tourism can bring financial rewards. [03:15.08]All the more reason to value these beautiful little creatures and their habitat, right?
[03:19.55]But to understand more about how to protect and support hummingbirds the best we can, we’ve gotta learn more about their breeding …nesting … sites and, uh, migration routes-and also about the natural habitats we find there. [03:34.82]That should help us determine how to prevent further decline in the population.
[03:39.47]A good research method ... a good way to learn more ... is by, um, running a banding study. [03:46.23]Banding the birds allows us to track them over their lifetime. [03:50.23]It’s a practice that's been used by researchers for years. [03:52.89]In fact, most of what we know about hummingbirds comes from banding studies ... where we, uh, capture a hummingbird and make sure all the information about it-like ... its weight and, um, age and length-are all recorded ... put into international... an international information database.
[04:11.95]And, then we place an extremely lightweight band around one of its legs … well, what looks like a leg-although, technically it’s considered part of the bird’s foot.
[04:21.86]Anyway, these bands are perfectly safe. [04:24.68]And some hummingbirds have worn them for years with no evidence of any problems. [04:29.14]The band is labeled with a tracking number …oh, and there’s a phone number on the band for people to call, for free, to report a banded bird they've found or recaptured.
[04:39.66]So when a banded bird is recaptured and reported, we learn about its migration route, its growth ... and how long it's been alive ... its life span. [04:49.66]One recaptured bird had been banded almost 12 years earlier! [04:54.35]She’s one of the oldest hummingbirds on record. [04:56.90]Another interesting thing we’ve learned is ... that some hummingbirds, uh, they no longer use a certain route; they travel by a different route to reach their destination. [05:08.57]And findings like these have been of interest to biologists and environmental scientists in a number of countries, who are trying to understand the complexities of how changes in a habitat... affect the species in it-species like the hummingbirds.