Narrator: Listen to part of a lecture in a biology class.
Professor: Yesterday, we were talking about survival techniques that animals use to endure harsh conditions. Today, um, I want to talk more specifically about hibernation—um, why some animals, mainly mammals, sleep through the winter. Now, many animals hibernate as a way to cope with food scarcity, but this isn’t the only way. Some animals have other adaptations, you know, such as migrating to warmer climates for the winter. Or, for example, the red fox actually grows a thicker coat and changes its diet.
Interestingly enough, what many think of as hibernation, in some species, is actually torpor, which is something like a light hibernation. They look similar, but they’re actually different. So, uh, what is it that signals an animal to hibernate? Can anyone name one thing that might signal to an animal that it’s time to start hibernating?
Male student: Uh, the temperature? You know, the animal starts to get cold, or its food supply dies with the season?
Professor: Good guess. That would seem like the obvious signal, right? The animal’s food supply dies or migrates and it knows to, well, gather up what it can and prepare its den or nest where it will stay. However, studies have shown that, uh, the length of the day and hormonal shifts are actually what trigger hibernation. So, well, as days get shorter, the animal knows that winter is approaching. In fact, hibernating animals enter hibernation at, um, around the same time every year. Regardless of the temperature or other external factors. We’re not going to go into the specific details right now, but these scientists point to an internal calendar that signals hormone shifts in the body.
Male student: I don’t understand—if there is still food available, why would the animal hibernate? Or if, say, it got colder earlier, why wouldn’t the animal hibernate then?
Professor: Right. Those would seem to be smart things for an animal to do, but consider how unpredictable weather can be. If hibernating and waking were completely weather-dependent, what would happen with an early frost in the fall or a warm day in the spring? It’s not like the hibernating mammal has a weather forecast that allows it to see that cold weather might continue even after the warm day. However, the length of day is a much more reliable indicator of the exact time of year, unlike the weather.
Okay, so these factors might be how the animal knows when to hibernate, but what about the why? We’re back to our original question. We know that hibernation is an adaptation to scarce resources, but why hibernate as opposed to say, migrating? Any ideas? No?
The key is the energy requirement for each option. A lot of energy is used in order for an animal to travel far enough to escape the winter climate, and then return, right? In fact, this is often why smaller mammals typically hibernate while larger ones often migrate. A larger animal can cover more distance with less effort, while a smaller animal doesn’t need as much energy to keep its small body warm during hibernation. Evolution, therefore, favors these advantages. Sarah, you have a question?
Female student: Um, yes, the idea that smaller animals are more likely to hibernate doesn’t make sense to me. Didn’t we discuss yesterday that many large bear species do not migrate. Why did they evolve to hibernate?
Professor: That’s a great question, and it comes back to a point I made earlier. Bears don’t actually hibernate, they enter torpor. Many of the processes of hibernation and torpor are the same, which is why they are often confused. Both, um, involve a reduction in body temperature, slowed heart rate and breathing, and even a restriction of blood to the main organs. However, a main difference seems to be whether the act is voluntary or involuntary.
Hibernation is actually a voluntary state, one, uh, that we know is triggered by hormones and day length, right? But, torpor appears to be involuntary—weather conditions seem to dictate this, and typically it will last for a short period of time, maybe just during the day or through the evening—depending on when the animal needs to be awake to hunt or forage for food. OK?
Now, before we move on, we need to examine one more activity similar to hibernation… and that is estivation. It is similar to the others… estivating animals become inactive and have lower heart and breathing rates. However, estivation is used by animals, such as, um… tortoises or even hedgehogs… to survive extremely hot and dry climates, not cold ones. Rather than staying warm and maintaining fat stores, this behavior can help keep an animal cool and preserve water stores.
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What does the professor mainly discuss? |
Gist-content. The professor is discussing sleep adaptations, mostly hibernation and torpor, and why these occur. |
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| ✓ | A When and why some animals engage in hibernation or torpor |
Correct. The professor primarily discusses long-term, deep forms of sleeping, such as hibernation and torpor, that are adaptations to changes in an animal’s environment. |
| ✗ | B Animal defense mechanisms in cold climates |
The forms of sleeping discussed in the lecture are not defense mechanisms, and they are reactions to hormonal shifts and changes in day length, not weather or climates. |
| ✗ | C The navigation techniques of species that migrate |
This issue is briefly mentioned by the professor, but is not the main focus of the lecture. |
| ✗ | D Hormonal shifts that control an animal’s internal calendar |
This concept is discussed by the professor, but is not the main point of the lecture. |
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According to the professor, why do smaller mammals typically hibernate rather than migrate? |
Detail. According to the professor, the basis of this choice was the amount of energy required. To travel far enough to migrate takes a lot of energy for small animals, but they do not need as much energy to keep themselves warm if they hibernate. |
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| ✗ | A They are more likely to be caught by predators if they migrate. |
Nothing stated by the professor indicates that this would be the case. |
| ✗ | B They are skilled at building underground dens. |
This idea is not mentioned in the lecture. |
| ✗ | C They are less likely to find food if they migrate. |
This idea is not mentioned in the lecture. |
| ✓ | D They need less energy to stay warm than to travel long distances. |
Correct. The professor explicitly states this in the lecture. |
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In order to determine whether an animal is in a state of hibernation or torpor, which of the following questions needs to be answered? |
Inference. The professor states that the primary difference is whether the state is entered into voluntarily or involuntarily. |
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| ✗ | A Whether the animal is large or small |
Size plays a role in the choice between hibernation and migration, not between hibernation and torpor. |
| ✓ | B Whether the act is voluntary or involuntary |
Correct. This is the primary difference noted by the professor. |
| ✗ | C The amount of food available |
Hibernation and torpor are both adaptations to food availability, among other factors. |
| ✗ | D The current weather conditions |
Hibernation and torpor are both adaptations to weather conditions, among other factors. |
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According to the professor, what are two triggers that determine when an animal enters into or awakens from hibernation? Choose 2 answers. |
Detail. The professor says that hormonal shifts and day length are the two triggers. She explicitly says it was not weather conditions or food availability, although those are primary reasons for the adaptation. |
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| ✗ | a Food availability |
This is a reason for the adaptation of hibernation, but not a trigger for it. |
| ✓ | b Hormonal shifts |
Correct. The professor said that hormonal shifts and day length are the two triggers. |
| ✓ | c Length of the day |
Correct. The professor said that hormonal shifts and day length are the two triggers. |
| ✗ | d Snowstorm frequency |
This idea is not mentioned in the lecture. |
Narrator: Listen again to part of the lecture. Then answer the question.
Professor: Studies have shown that, uh, the length of the day and hormonal shifts are actually what trigger hibernation. So, well, as days get shorter, the animal knows that winter is approaching. In fact, hibernating animals enter hibernation at, um, around the same time every year. Regardless of the temperature or other external factors. We’re not going to go into the specific details right now, but these scientists point to an internal calendar that signals hormone shifts in the body.
Narrator: What does the professor mean when she says this:
Professor: We’re not going to go into the specific details right now, but these scientists point to an internal calendar that signals hormone shifts in the body.
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What does the professor mean when she says this? |
Speaker’s Attitude. In the highlighted quote, the professor has decided not to provide certain specific details. Instead, she focuses more on a general point. |
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| ✗ | A She has already covered the details in an earlier class. |
The professor does not indicate that this is the case. |
| ✗ | B She is not confident enough about the details to explain them. |
Nothing in the lecture suggests that the professor is not confident about the details of hibernation triggers. |
| ✓ | C She does not want to discuss details that are not relevant to her main point. |
Correct. The professor does not state her reasons. But it is implied that she would rather conclude this specific point and move on than provide more detail. |
| ✗ | D She believes that the explanation is too complicated for the students to understand. |
This is possibly a reason for the professor not continuing. But it is not certain. What is known is that the professor wishes to move on to discussing her more general point. |
Narrator: Listen again to part of the lecture. Then answer the question.
Male student: I don’t understand—if there is still food available, why would the animal hibernate? Or if, say, it got colder earlier, why wouldn’t the animal hibernate then?
Professor: Right. Those would seem to be smart things for an animal to do, but consider how unpredictable weather can be. If hibernating and waking were completely weather-dependent, what would happen with an early frost in the fall or a warm day in the spring?
Narrator: What point does the professor make when she says this:
Professor: If hibernating and waking were completely weather dependent, what would happen with an early frost in the fall or a warm day in the spring?
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What point does the professor make when she says this? |
Function of What Is Said. In this quote, the professor is indicating that weather is an unreliable guide for when to begin, or end, hibernation, because weather can vary substantially from day to day. |
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| ✗ | A It is not clear how animals know whether to hibernate or migrate. |
On the contrary, the professor has explained this earlier in the lecture. |
| ✗ | B Different animals hibernate at different times of the year. |
This might be the case, but this is not the point the professor is making. |
| ✗ | C The changing temperature might prevent animals from migrating. |
This quote is not about migration. It is about the timing of hibernation. |
| ✓ | D Animals might hibernate at the wrong time if they only use weather signals. |
Correct. Because weather can vary substantially from day to day, animals may enter into or end hibernation at the wrong time if weather is the basis for the decision. |