Narrator: Listen to part of a lecture in an environmental science class.
Professor: So, last week we covered issues regarding, um, how humans impact animal habitats, specifically the negative impact… how habitats are declining or have been destroyed completely. For example, deforestation—cutting down acres of trees where some animals hunt and live—has an obvious impact on an animal population. There are, of course, unexpected impacts, um… that might not be obvious—impacts that can occur either before or after an animal population has declined. Today, I want to talk about a specific example of this type of… unexpected—and, honestly strange—way that humans have affected a species… the chimney swift.
Well, chimney swifts… you might not have heard of these birds, but they are—well were—common in the Eastern United States and Canada during the summer. During the winter months, they migrate to South, um… South America… to the upper Amazon basin of Ecuador, Brazil, Chile, and Peru. They’re most common in, um, areas with many chimneys, as this is where they nest, um… hence the name—chimney swift. However, when traveling across rural areas you might find them nesting in trees, especially hollow trees, or even caves.
Now, nesting for chimney swifts is a very unique experience—get this—they actually can’t perch! That is, they can’t sit or stand on branches. In fact, um, they can’t even stand or walk at all, not even on the ground! They spend almost all their lives airborne… they eat, and even bathe, while flying. The only time they are not in flight is when they are nesting or roosting. Remember that a nest is for incubating… hatching eggs and raising young, while a roost is a place where a bird sleeps. But when they are nesting or roosting, chimney swifts must cling to the side of an enclosure… which is why a chimney is such a perfect home, right?
Well, chimney swifts have been in a long-term decline throughout their migration range. In fact, in 2010, they were added to the list of near-threatened bird species in North America. But why the decline? Would you guess that it is partially because more and more houses and apartment buildings are being built without chimneys? And, um, even those older homes with chimneys, well… their owners are often capping or sealing off the chimneys.
Those chimneys that are being built… they’re just not made the same as they used to be. Old chimneys were typically brick or some type of masonry, maybe concrete, so there was a surface that the bird could attach itself and its nest to. But newer construction—newer chimneys—are often lined with metal… and the birds cannot cling to that smooth surface. And I don’t need to tell you, but… a population that cannot find places to live and nest will struggle to survive.
But changing fireplaces isn’t the only thing that’s had an unexpected impact on the chimney swift population. Some scientists have started to study the roosting and nesting locations of the swifts. See, these birds will return to the same nesting site year after year… the young will even return to the nest where they were born to set up their own nest. These scientists have noticed that even when nesting locations are still suitable—no chimney cap or liner has been added—fewer and fewer birds are returning. These researchers blame pesticides, especially residential pesticides. You see, chimney swifts are actually quite useful because they feed on all sorts of flying and biting insects—particularly, um, mosquitos, biting flies, wasps, and even fire ants. However, people don’t like getting bitten while trying to enjoy a backyard barbeque. With more people buying supplies at the local lawn and garden store to kill these pests, well… I’m sure you can guess what happens to chimney swifts when they don’t have enough insects to feed on.
Remember that these birds spend essentially all their time flying—an activity, uh, that uses a considerable amount of energy. And yes, they are quite small—most weigh about an ounce—but they eat over a third of their weight in insects each day!
Most of the focus on conservation of the species is, well… on habitat. Many municipalities are trying to encourage homeowners to leave their chimneys uncapped, at least during summer, when the swifts are nesting. Some places are even building chimney swift “towers” and placing them in fields and parks.
In general, the conservation efforts have focused on informing the general population of this species—showing how useful they can be at pest control, for example. Across their habitat range, groups are even setting up annual chimney swift “sits” to get people interested in the bird. People report the presence of a roost or nest, and then get together with friends to sit and watch the swifts coming and going—a nice excuse to spend a pleasant evening outdoors.
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What does the professor mainly talk about? |
Gist-content. The professor primarily talks about the chimney swift and challenges it is currently facing due to changes in human activities. |
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| ✗ | A Changes in the migration patterns of chimney swifts |
Specifics of their migration patterns are never mentioned. |
| ✓ | B Causes of the decline in chimney swift populations |
Correct. This lecture focuses on the loss of suitable nesting sites and the reduction of food sources due to pesticide use. |
| ✗ | C Where chimney swifts nest in rainforests |
There was no discussion of rainforests in the lecture. |
| ✗ | D Health risks of residential pesticides |
Residential pesticides are possibly diminishing food sources for chimney swifts, but nothing is mentioned about health risks. |
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What does the professor imply might be causing a decline in the chimney swift population? |
Inference. The professor notes two likely causes: changes in the number of chimneys and how they are built, and residential pesticides. |
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| ✗ | A Deforestation along their migration routes |
Deforestation along migration routes was never mentioned. |
| ✗ | B An increase in hunting activity |
Human hunting was never mentioned in the lecture. |
| ✓ | C A decrease in the number of homes with uncapped or unsealed chimneys |
Correct. The professor mentions that a possible cause of the population decline is that “more and more houses and apartment buildings are being built without chimneys,” and that existing chimneys are often being capped or sealed off. |
| ✗ | D A change in the birds’ migration patterns |
A change in migration patterns was never mentioned. |
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What does the professor say about how the use of pesticides affects chimney swift populations? |
Detail. The professor states that it may be reducing the food supply of the chimney swift. |
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| ✗ | A Pesticides are poisoning chimney swift populations. |
Pesticides are killing the prey of chimney swifts, not the birds themselves. |
| ✗ | B Pesticides are an effective way to reduce parasites that are harmful to chimney swifts. |
Chimney swift parasites are never mentioned in the lecture. |
| ✗ | C Pesticides have little or no impact on chimney swift populations. |
On the contrary, pesticides are likely responsible for reducing the bird’s natural food supply. |
| ✓ | D Pesticides kill the primary food sources of chimney swifts, making food harder to find. |
Correct. The professor lists wasps, ants, mosquitos, and other yard pests as the primary food sources for chimney swifts. She also notes that many residents are using pesticides to kill them off. |
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According to the professor, how are some scientists estimating the decline in the chimney swift population? |
Detail. Chimney swifts usually return to the same nesting locations each year, so scientists are tracking the number of birds that return to known nesting sites. |
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| ✓ | A Counting the swifts that return to suitable nests each year |
Correct. The professor states that, because chimney swifts return to the same nesting sites year after year, scientists count the number of birds that return to each nest to estimate population changes. |
| ✗ | B Collecting estimates from people who report seeing a chimney swift nest |
The professor indicates that people are setting up chimney swift “sits” to increase interest in the bird, but not to track population numbers. |
| ✗ | C Tracking the birds with radio-frequency identification tags |
This practice is never mentioned in the lecture. |
| ✗ | D Constructing swift “towers” to attract the birds |
People are building swift “towers” to provide new places for the swifts to nest or roost in response to the loss of suitable chimneys, but scientists are not doing this to track population numbers. |
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What does the professor imply about bird perching? |
Inference. The professor states that “nesting for chimney swifts is a very unique experience… they actually can’t perch!” The implication is that the inability to perch is unusual for a bird. |
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| ✗ | A Most birds only perch in a nest. |
The common locations for birds to perch in general are not mentioned. |
| ✗ | B A bird is more vulnerable to attack when perched. |
There is no discussion about what leaves a bird vulnerable to attack. |
| ✗ | C Perching is essential for migrating chimney swifts. |
There is little discussion about the migration of chimney swifts. |
| ✓ | D The majority of birds can perch. |
Correct. The professor mentions that nesting for chimney swifts is unique in that they cannot perch. This implies that most birds are able to perch. |
Narrator: Listen again to part of the lecture. Then answer the question.
Professor: Those chimneys that are being built… they’re just not made the same as they used to be. Old chimneys were typically brick or some type of masonry, maybe concrete, so there was a surface that the bird could attach itself and its nest to. But newer construction—newer chimneys—are often lined with metal… and the birds cannot cling to that smooth surface. And I don’t need to tell you, but… a population that cannot find places to live and nest will struggle to survive.
Narrator: What does the professor imply when she says this:
Professor: And I don’t need to tell you, but…
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What does the professor imply when she says this? |
Function of What Is Said. The phrase “and I don’t need to tell you, but…” means that the speaker believes that what she is about to say is an obvious consequence of what she just finished saying. |
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| ✗ | A She does not think her next point is important enough to share. |
This expression does not indicate importance, or lack thereof. It indicates that what follows is obvious. |
| ✓ | B Students are likely to find her next point obvious. |
Correct. She uses this phrase because she believes that her students probably could already figure out what she says next. |
| ✗ | C She is unsure about her next point. |
This comment has nothing to do with her confidence in her next point. |
| ✗ | D She believes the next point will confuse students. |
On the contrary, she believes they probably could already figure out what she says next. |