Most of the year, the hermit thrush, a North American songbird, eats

Question

Most of the year, the hermit thrush, a North American songbird, eats a diet consisting mainly of insects, but in autumn, as the thrushes migrate to their Central and South American wintering grounds, they feed almost exclusively on wild berries. Wild berries, however, are not as rich in calories as insects, yet thrushes need to consume plenty of calories in order to complete their migration. One possible explanation is that berries contain other nutrients that thrushes need for migration and that insects lack.

Which of the following, if true, most seriously calls into question the explanation given for the thrush’s diet during migration‘?

Which of the following, if true, most seriously calls into question the explanation given for the thrush’s diet during migration?

(A) Hermit thrushes, if undernourished, are unable to complete their autumn migration before the onset of winter.

(B) Insect species contain certain nutrients that are not found in wild berries.

(C) For songbirds, catching insects requires the expenditure of significantly more calories than eating wild berries does.

(D) Along the hermit thrushes’ migration routes, insects are abundant throughout the migration season.

(E) There are some species of wild berries that hermit thrushes generally do not eat, even though these berry species are exceptionally rich in calories.

Thrush Migration

Step 1: Identify the Question

The words calls into question indicate that this is a  Weaken the Argument  question.

Step 2: Deconstruct the Argument

T: usually eat insects

But migrate eat berries even tho fewer cal

Ó Berries nec nutrients

Step 3: Pause and State the Goal

On Weaken questions, the correct answer makes the conclusion less likely to be valid. The conclusion in this argument is a possible explanation for the thrush’s feeding behavior. One way to weaken this conclusion is to provide an  alternative reason for this behavior .

Step 4: Work from Wrong to Right

(A) This information explains why nutrition is important for the thrush during migration. It does not, however, address why the thrush eats berries instead of insects.

(B) This answer provides another reason it might be better for thrushes to eat insects (other specific nutrients). It does not provide an alternative reason as to why thrushes eat berries.

(C) CORRECT . This answer provides an alternative reason that thrushes might choose to eat berries instead of insects while migrating: They don’t want to expend extra energy catching the insects. Even though the berries contain fewer calories, the thrushes might actually have a net gain of calories since they don’t have to chase and capture the berries.

(D) If insects are very abundant along the migration route but the thrush still prefers berries, then the conclusion is more likely to be valid, not less.

(E) The argument states that thrushes do eat berries while migrating. The fact that they do not eat all types of berries does not influence the explanation as to why they eat some berries.

akhil911 · Accepted Answer

Premise - Hermits feed on insects most of the times but during migration they feed on wild berries though wild berries are not as rich in calories as insects are and Hermits require plenty of calories during migration.
Conclusion - Berries contain other nutrients that Hermits need for migration and that insects lack.

If we want to weaken the conclusion we should look for a choice which provides an alternate reason as to why the Hermits prefer eating berries during Migration.

There could be various reasons one can think of 
- It is possible that no insects are available that the Hermits can eat during migration.
- Or some other reason.

A. Hermit thrushes, if undernourished, are unable to complete their autumn migration before the onset of winter.
- There is not mention of undernourishment in either the premise or the conclusion. This statement does not affect the conclusion in any way.

B. Insect species contain certain nutrients that are not found in Wild berries.
- This statement too does not affect the conclusion. Even if Insect species contain certain nutrients that are not found in berries , this choice does not provide any reason as to why the hermits prefer berries to insects during migration.

C. For songbirds, catching insects requires the expenditure of significantly more calories than eating wild berries does.
- This choice provides an alternate reason to the fact that hermits prefer berries. If catching insects requires significantly more calories than catching wild berries does then the hermits by choice have berries because they would want to conserve energy during their migration.

D. Along the hermit thrushes’ migration routes, insects are abundant throughout the migration season.
- Does not provide any reason as to why hermits prefer berries.

E. There are some species of wild berries that hermit thrushes generally do not eat, even though these berry species are exceptionally rich in calories.
- Does not affect the conclusion. Even if there are some species that are rich and hermits do not eat them this choice does not provide any alternate cause.

GMATNinja · Answer

Let's review the situation:

The birds need plenty of calories in order to complete their migration. 
 Berries are not as rich in calories as insects. 
 If the birds need lots of calories and insects are higher in calories, why do the birds eat berries during migration instead of insects?? 
 "One possible explanation is that berries contain other nutrients that thrushes need for migration and that insects lack."

We are looking for an answer choice that calls this explanation into question. We don't need to  prove  that the explanation in the passage is false. However, if one of the answer choices provides a plausible  alternative  explanation, then that would cause us to doubt the explanation given in the passage.

Remember, the birds need plenty of calories. We know that insects are higher in calories, but now we are told that the birds expend significantly more calories  getting  those calories from the insects. So even though the insects are high in calories, the birds have to waste a lot of calories catching the insects. If the goal is to achieve the highest  net  balance of calories, then the birds might be better off eating the berries.

Again, we don't need to  prove  that eating berries will lead to a higher net balance of calories. But this is certainly a plausible explanation for the phenomenon described in the passage. Since we now have a plausible alternative explanation, the explanation given in the passage is certainly called into question. (C) looks good.

We are trying to explain why the birds eat berries instead of insects. If the insects were NOT abundant, that might explain why the birds eat berries. But if the insects ARE abundant, then the birds should have no problem finding them. So why are they eating berries instead? Choice (D) does not explain the apparent discrepancy, so eliminate this one.

(E) simply tells us that the birds avoid some high-calorie berries. But we already know that the birds eat berries during migration and that the berries are lower in calories than insects. (E) does not explain why the birds chose the lower-calorie option, so eliminate this one.

(C) is the best answer.

monk16 · Answer

NA song bird diet mainly consist of insects

In autumn they migrate to Central and South America where their
diet is exclusively wild berries

wild berries are low in calories

the possible reason could be it has some other nutrients that they need for migartion that insect lacks.Conclusion

we have to find a reason other than nutrients to explain the birds eating habit.

Option C : this gives a counter opinion for the conclusion ,since the calories expelled was more for insect catching , the birds feed on wild berries

Abhishek009 · Answer

Thrush : Most of the year---> Insects
Thrush : Autumn ------------> Wild Berries
Calories : Wild Berries < Insects
So , Thrushes need plenty of Wild Berries to complete their migration.
Possible reason : Berries contain other nutrients not found in Wild Berries

Prethink : What's the reason that Thrushs consume only Wild Berries not Insects during migration ? Check the answers -

A. Hermit thrushes,  if undernourished, are unable to complete their autumn migration   before the onset of winter.

Out of scope , this options talks about undernourishment.

B. Insect species contain certain  nutrients that are not found in Wild berries.

Out of scope , this options talks about other nutrients which is not under discussion in the present context.

C. For songbirds,  catching insects requires the expenditure of significantly more calories than eating wild berries does.

Calorie Used : Catching Insects > Eating wild berries ; for same calorific intake...
 
Say 10 KCAL of Energy is consumed ...

Catching Insects = 4KCAL
Eating wild berries = 3 KCAL
Energy Requirement for flight = 5KCAL

Keeping in mind that the bird requires energy for flight it is definitely beneficial for the bird to use it economically and consume high calorie food/nutrients...
 
D. Along the hermit thrushes’ migration routes,  insects are abundant throughout the migration season.

So, why do the birds not catch insects ? Can not weaken the conclusion.

E. There are  some species of wild berries that hermit thrushes generally do not eat , even though these berry species are exceptionally rich in calories.

Completely out of scope and irrelevant under present context..
  
Hence IMHO definitely with (C)

LogicGuru1 · Answer

C is the unopposed winner 
 
Insect gives 100 calorie; Catching insect requires bird to lose 40 calorie. (Finding insect, Flying, then chasing insect, then breaking its shell). 
Birds net calorie gain from insect 100-40=60 calorie

Berries gives only 80 calories, But finding berry requires 10 calorie. Find a tree and hop and hop and eat as much as you like without any problem. 
Birds Calorie gain from berries 80-10=70 calorie.

Therefore the songbird eats only berries to gain as much calorie as they can. Chasing and catching insect is not viable for songbirds.
What option reconfirms our conclusion
 
 C. For songbirds, catching insects requires the expenditure of significantly more calories than eating wild berries does.

AbhiGarg2007 · Answer

ChiranjeevSingh  , Why is option D wrong here ? If birds find insects on route , then probabaly the calories gained to complete migration are not from berries but from Insects.

Although C is a promising answer , question specifically asks for diet's during migration ? While option C indicated the situation before Migration. Also when birds about to start their journey, they need to accumulate certain value of calories say 100J , no matter how much they spend calories during accumulation process.

Please help !

ChiranjeevSingh · Answer

Option D is wrong because OG says so!

The point we are trying to explain here is why don't they eat insects in autumn. Right? We are not saying that they don't eat insects in North America; we are saying that they don't eat insects at all in autumn! And now option D tries to explain so by saying that they have insects during their routes! Wow! Then, why don't they eat them? We're stuck on the same question! Nowhere does option C indicate that it is about "before migration". or am I missing something? Is it? Energy expended doesn't matter? If you eat 100J and spend 100J, then how much do you have left? - CJ

arvind910619 · Answer

The logic of the question is why the birds prefer to eat wild berries when they need very large amounts of energy while migrating .
We have show that this particular behavior is the most efficient one

C gives us the reason why birds prefer to eat wild berries when they migrate they reduce their energy by not catching insects .

rahul2013 · Answer

What i need to find - During Migration Thrush doesn’t eats wild berries just because berries got more other nutrients .

option Analysis -
A. Where is berries explanation
B. ok still why berries ?
C. That explains
D. then why berries ?
E. some right… May be exceptions here

auradediligodo · Answer

Most of the year, the hermit thrush, a North American songbird, eats a diet consisting mainly of insects, but in autumn, as the thrushes migrate to their Central and South American wintering grounds, they feed almost exclusively on wild berries. Wild berries, however, are not as rich in calories as insects, yet thrushes need to consume plenty of calories in order to complete their migration. One possible explanation is that berries contain other nutrients that thrushes need for migration and that insects lack.

Which of the following, if true, most seriously calls into question the explanation given for the thrush’s diet during migration‘?

Which of the following, if true, most seriously calls into question the explanation given for the thrush’s diet during migration?

Pre-thinking
 The author's assumption here is that the hermit thrush eats the same amount of berries and insects. But since the thrush needs plenty of energies for migration there must be some extra nutrients in berries than in insects otherwise it will be unlikely that the thrush will complete migrations.

Our task is to weaken this reasoning.
#1 Let's say that the hermit thrush when migrating eats double the amount it usually eats when he normally eats insects.  
 This clearly weakens the author reasoning because now we can see how the thrush could eat even more calories than when eating insects.

#2Think also about energy consumption in a more specific way for the thrush. When does it consume energy? It consumes energy when it migrates and when it hunts for food. Now probably chasing insects requires more energies than finding berries (note that could also be the reverse scenario. this is just a case). So this would suggest that even if berries have fewer calories than insects and even if the thrush eats the same amount of berries and insects the total energy consumption might be the same

(A) Hermit thrushes, if undernourished, are unable to complete their autumn migration before the onset of winter.
 We are concerned with proving or disproving that berries have certain nutrients that insects don't have. Hence this choice is irrelevant and incorrect

(B) Insect species contain certain nutrients that are not found in wild berries.
 This is a point in favor for the insects but definitely it does not weaken the conclusion. Hence incorrect

(C) For songbirds, catching insects requires the expenditure of significantly more calories than eating wild berries does.
 Don't fall into the trap "wrong entity hence wrong answer" because  hermit thrushes are songbirds . This choice suggests that the energy consumption made for eating insects is higher than the one for eating berries. Hence this is another possible explanation and no extra nutrients are needed for the thrush to migrate. Hence correct

(D) Along the hermit thrushes’ migration routes, insects are abundant throughout the migration season.
 We are already told that thrushes during migration are going to eat only berries. So this information goes against the information of the argument. Hence incorrect

(E) There are some species of wild berries that hermit thrushes generally do not eat, even though these berry species are exceptionally rich in calories.
 if they don't eat them these berries are outside of our concern

sagarsangani123 · Answer

Migration requires thrushes to consume a lots of calories. During migration, thrushes exclusively depends on Wild berries. Despite not being rich in calories as insects, thrushes contain other nutrients needed during migration that insects lack. One evident gap here is that the author is assuming that the nutrients that wild berries contain and insects lack and are required for migration, can compensate for the 'calories' required to complete the migration. 
 
Which of the following, if true, most seriously calls into question the explanation given for the thrush’s diet during migration?

(A) Hermit thrushes, if undernourished, are unable to complete their autumn migration before the onset of winter - We don't know whether consuming Wild berries would be sufficient nourishment for Hermit thrushes to complete the migration. Thus it doesn't call into question the explanation given for thrush's diet during migration.  Reject

(B) Insect species contain certain nutrients that are not found in wild berries - Question asks to cast doubt on the explanation to 'why despite not being rich in calories, wild berries form a part of diet for thrushes during migration in autumn'. This answer choice doesn't address this point.  Reject

(C)  For songbirds, catching insects requires the expenditure of significantly more calories than eating wild berries does - Thus the songbirds are saving energy (calories) by eating wild berries. Though insects are calorie-rich source for the songbirds, during migration if the expenditure of calories is more for catching insects, then it would limit the calories required for migration. Maybe this is the reason to exclusively depend on Wild berries. Despite providing less calories as compared to consuming insects, thrushes also spent less calorie to eat wild berries, thus overall having more calories for migration. This gives us an alternate explanation and thus calls into question the explanation given for thrush's diet during migration. In other words, it is not that berries contain nutrients that insects lack is the reason for thrushes to eat berries, but instead the reason for thrushes to eat berries is the calorie-savings.

(D) Along the hermit thrushes’ migration routes, insects are abundant throughout the migration season - This distracts us by saying that insects are abundant along the hermit thrushes' migration routes. Are wild berries abundant as well? We don't know. -  Reject

(E) There are some species of wild berries that hermit thrushes generally do not eat, even though these berry species are exceptionally rich in calories. - This is a general fact about the diet of hermit thrushes. We do not know whether these species of wild berries are available during autumn. Also, the question asks to cast doubt on the explanation that stated preference of wild berries over insects and not over other species of wild berries. -  Reject

Lohit1006 · Answer

Gmat  NINJA  Gmat  Club Experts
Could you explain the below?

The first sentence (PREMISE) and Option-C are contradicting.
"Most of the year, the hermit thrush, a North American songbird, eats a diet consisting mainly of insects" -> If most of the year, hermit thrush is able to spend calories to catch & eat insects, then it is contradicting option-(C)'s alternate explanation..

egmat · Answer

Hello Lohit,
Let me help you here!

The wild berries diet belongs to a season where the thrushes need to complete their migration. What option C indicates is that the wild berries, even though they contain lesser calories than insects, do not demand energy expenditure to find and consume. So, it is probable that the net calories added by the thrushes through the wild berry diet are the same as or even higher than the insect diet. Thus, it provides an alternate cause instead of the conclusion as an explanation to the behaviour of eating berries.

Hope this clarifies the case!
Best regards,
Arathy

woohoo921 · Answer

Are Choices (A) and (B) just simply put... out of scope? If anything, Choice (B) could even be seen as a weakener, correct? Thank you in advance

MartyTargetTestPrep · Answer

Well choice (B) does not really change the scenario. The passage says that berries contain other nutrient that insects lack. What (B) says, that insects contain nutrients that berries lack doesn't make any difference since the thrushes have been eating insects and thus have consumed those nutrients.

Also, (A) helps to explain why the thrushes need the nutrients. We don't need an explanation though. We need a weakener.

Elite097 · Answer

ThatDudeKnows MartyTargetTestPrep GMATNinja anish @gmatextensive here why are we looking for an alternate explanation? We already that the passage gives us one "possible" explanation so it leaves room for other explanations too. egmat

ALos what exactly is the conclusion? Very hard to figure.

Why not B

ALos what exactly is the conclusion? Very hard to figure.

Why not B

MartyTargetTestPrep · Answer

The conclusion is "One possible explanation is that berries contain other nutrients that thrushes need for migration and that insects lack."

It's not a firm conclusion that that explanation it the correct one, but it's the only conclusion presented by the passage.

The question asks us to find the choice that "most seriously calls into question the explanation given for the thrush’s diet during migration."

Even though the passage terms the explanation offered "one possible explanation," a choice that provides a rather plausible alternative explanation still serves to call into question the explanation offered by the passage. In other words, the existence of a plausible alternative explanation makes it less probable that the "possible explanation" offered by the passage is the correct one.

Elite097 · Answer

Thanks  MartyTargetTestPrep  and why not B

MartyTargetTestPrep · Answer

(B) doesn't really change anything. Regardless of what nutrients the insect contain that berries don't, it could be that the reason the thrushes eat the berries is that berries contain nutrients that the thrushes need and insects lack.

Also, the fact that the passage says that thrushes have been eating insects "for most of the year" helps to make (B) incorrect since it's possible that any nutrients that thrushes get from insects but not from berries the thrushes have loaded up on already.

Most of the year, the hermit thrush, a North American songbird, eats

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Most of the year, the hermit thrush, a North American songbird, eats

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