模拟测试卷2-2019-8月新卷 How did researchers find out what a bird ate at different times during migration?

[00:00.00]Narrator: Listen to part of a lecture in a biology class.[00:08.60]Professor:Okay. So we spent a lot of time this past week talking about migratory birds and how they survive their long journey. [00:16.84]Well, there’s some interesting research that’s being done to determine what certain migratory birds eat during their journey, and more importantly, what they eat at different times during migration.[00:30.15] And this research involves using breath collector tiny breath collectors.[00:35.67] Here’s how it works. It consists of a small mass connected to a small balloon filled with oxygen.[00:43.91] The mask is fitted over the bird’s beak and the bird inhales the oxygen from the balloon, and then when it exhales, it replaces the oxygen with carbon dioxide,[00:55.63]so then researchers analyze the carbon dioxide for the carbon signature of the food the bird ate recently.[01:04.54] Now the carbon signature that the researchers measure is the ratio of carbon 12 to carbon 13, two different forms of carbon in the bird’s breath. [01:16.53]And the ratio will vary depending on what the bird ate.
[01:20.67]Male:You said they could determine what a bird at different times during migration. How do they do that?[01:27.84]Professor:Well, good question. What happens is that over a period of time, as the bird digests its food, and the body absorb the nutrient, the carbon signature move from the bird’s breath, to its blood, and then to its feathers. [01:44.44]The carbon signature in the breath tells us what the bird ate earlier that day.[01:50.07] The signature in the blood plasma tells us what it ate two or three days before and the signature in the red blood cells tells us what it ate two or three weeks before,[02:02.92] and finally the carbon signature in the bird’s feather tells us what it ate a month or so ago. [02:10.34]So scientists can basically create a dietary record by analyzing a bird’s breath along with a carbon signature in different tissues from the same bird. [02:22.12]Okay, so what if the carbon signature in a bird’s feather is different than the carbon signature in its breath?
[02:30.33]Male:That would tell us that the bird changed its diet over the course of its migrating, wouldn’t it?[02:37.06]Professor:Yes, it would In fact, that’s what tests revealed about white-throated sparrows on Block Island. [02:44.07]We learned that during the course of their migration, white-throated sparrows switched their diet from berries to corn when at a stopover sight on Block Island. [02:56.04]Now, this indicates that they’re eating at bird feeder because that’s an ingredient in bird feed and there’s no corn grown on this particular island. [03:06.85]So researchers know that birds are using bird feeder, but they don’t know why. Is it because there’s not enough of the food they usually eat available to them?[03:18.02] Or is it because they prefer corn? So we need to know, do the sparrows usually switch to their diet when they migrate? Is this a more nutritious diet for the migration period?[03:30.93] Or are they just getting by on corn, when what they really need is berries? This raises the question about the importance of feeders to the birds as they migrate. [03:42.71]If we can understand the sparrow’s diet, we can provide them with proper nutrition while they are migrating. [03:50.57]On top of that, Block Island used to have a lot of farming, but now residents rely on tourism. Tourists often come to see the flocks of migrating birds.
[04:02.25]Male:So when you talk about proper nutrition for the sparrows, it could be corn. It could be berries.[04:12.95]Male:So, what about other animals? Could breath collectors be used to find out about their diet?[04:19.12]Professor:Yes. Of course, you need a different size mask. This research is not only significant to biologists studying birds. [04:28.69]For instance, biologists are studying the eating habits of bears to find out if they eat different foods when they’re nursing than when they’re not nursing because they want to know whether nursing bears are more carnivorous than non-nursing bears. [04:45.50]How would you like to be the biologist who puts the mask on the bear? Of course, the bears are sedated before that’s done, so it’s not as risky as it might seem. [04:56.88]Anyway, similar research is being conducted all over the world since the information it provides could be very useful to conservation efforts.