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AndrewN

Please evaluate my reasoning for option A.
I think option A is a weakener.
Because option A gives another reason for CJ's to migrate southward.
Basically this option says is that they don't migrate south because of lack of navigational ability but because they lay their eggs there.
Hence, this kind of works as a weakener.

Please evaluate my reasoning.
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AndrewN

Please evaluate my reasoning for option A.
I think option A is a weakener.
Because option A gives another reason for CJ's to migrate southward.
Basically this option says is that they don't migrate south because of lack of navigational ability but because they lay their eggs there.
Hence, this kind of works as a weakener.

Please evaluate my reasoning.
Hello, krndatta. Option (A) could provide a reason for why the Croton's jays migrate southward, but we then have to presuppose that the jays know to follow the crookbeaks for the purpose of parasitic nesting, and such a consideration has little to do with how the jays migrate: whether they do or do not possess sufficient navigational abilities to make their way on their own. I saw you post a fine response in a different thread just a bit ago in which you advised someone to stick to exactly what the passage says. Here, we are aiming to strengthen the argument. If the argument is based on how the jays get from point A to point B, then we should focus on how, not why.

Perhaps that clarifies the matter. Thank you for thinking to follow up with me.

- Andrew
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AndrewN

Thanks for the praise.
So basically option A is giving us a "why" they migrate south? We are not concerned with the "why".
We have to focus on the "how" part.
Hence, this is a neutral statement.

Am I right?
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AndrewN

Thanks for the praise.
So basically option A is giving us a "why" they migrate south? We are not concerned with the "why".
We have to focus on the "how" part.
Hence, this is a neutral statement.

Am I right?
Yes, it does not affect the argument. (I typically avoid one-word tags such as "irrelevant," since I think such a terse treatment of an answer choice does little to explain the thought process behind that word.)

Quote:
Clearly, therefore, Croton's jays lack the navigational ability to find their way south on their own.

Which of the following, if true, most strengthens the argument above?
Ask yourself a question when you consider the answer choices. Does this information support the idea that the jays lack the navigational ability to [migrate]?

Quote:
(A) Croton's jays lay their eggs in the nests of crookbeaks, which breed upon completing their southern migration.
Again, this information may tell us why the jays follow the crookbeaks, but it provides no insight into the argument itself.

1) The jays lack navigational abilities, so they follow the crookbeaks to lay eggs in their nests.

—OR—

2) The jays do not lack navigational abilities, but they follow the crookbeaks anyway to lay eggs in their nests.

We cannot lean on information in the passage or answer choice to push us into a certain interpretation. Now, I agree that (C) is not the strongest strengthener, but if the jays always seem to migrate in the company of other birds, whether north or south, then the hypothesis that they are not navigationally inclined gains traction (even if it ends up being inaccurate).

- Andrew
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Hi GMATNinja KarishmaB MartyMurray IanStewart ChiranjeevSingh

I am not very clear why option C is the correct one. The conclusion clearly talks about navigational ability to south i.e. X whereas option C talks about north (Y). How does knowing about migration to Y can increase our confidence in X because the conclusion is not a general one that they lack navigational ability for any direction.

In option D, "occasionally" means rarely, if other species rarely accompany crook-beaks then it increases my confidence that Croton's Jays accompany crook-beaks because they lack the navigational ability to south. Why this is wrong?

Please let me know where I am going wrong.
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Hi GMATNinja KarishmaB MartyMurray IanStewart ChiranjeevSingh

I am not very clear why option C is the correct one. The conclusion clearly talks about navigational ability to south i.e. X whereas option C talks about north (Y). How does knowing about migration to Y can increase our confidence in X because the conclusion is not a general one that they lack navigational ability for any direction.

In option D, "occasionally" means rarely, if other species rarely accompany crook-beaks then it increases my confidence that Croton's Jays accompany crook-beaks because they lack the navigational ability to south. Why this is wrong?

Please let me know where I am going wrong.

Hi agrasan. This is an interesting question.

Keep in mind that different CR's require a different approach and have a different standard when it comes to the correct answer. Some you must have infallible watertight argument and for some just a bit of strengthening does the job. In this case, just a bit of strengthening is all that is asked for.

So how can you strengthen the argument that those Jays lack navigational abilities?
One answer could be that they don't fly on their own or never fly on their own or something along those lines and C) is exactly that - it tells us that they fly with one bird north while they fly with crookbeaks south. So they are not attached to the birds but clearly need help.

D. talks about other species and that does not help us in strengthening. That weakens if anything because it says that following Crook-beaks is a common or popular thing to do, so it does not mean Jays are bad at navigating.
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Hi GMATNinja KarishmaB MartyMurray IanStewart ChiranjeevSingh

I am not very clear why option C is the correct one. The conclusion clearly talks about navigational ability to south i.e. X whereas option C talks about north (Y). How does knowing about migration to Y can increase our confidence in X because the conclusion is not a general one that they lack navigational ability for any direction.

In option D, "occasionally" means rarely, if other species rarely accompany crook-beaks then it increases my confidence that Croton's Jays accompany crook-beaks because they lack the navigational ability to south. Why this is wrong?

Please let me know where I am going wrong.

agrasan - I see that BB has already responded to your query so I know we are good there.
The point you raised reminded me of another question which has a similar pattern. I am giving the link to that here. The pattern in these questions is acceptable, just like you would find it acceptable in real life too.

https://gmatclub.com/forum/studies-in-r ... l#p1138358
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Every fall Croton's jays migrate south. The jays always join flocks of migrating crookbeaks with which they share the same summer and winter territories. If a jay becomes separated from the crookbeaks it is accompanying, it wanders until it comes across another flock of crookbeaks. Clearly, therefore, Croton's jays lack the navigational ability to find their way south on their own.

The conclusion of the argument is the following:

Clearly, therefore, Croton's jays lack the navigational ability to find their way south on their own.

The support for the conclusion is the following:

The jays always join flocks of migrating crookbeaks with which they share the same summer and winter territories. If a jay becomes separated from the crookbeaks it is accompanying, it wanders until it comes across another flock of crookbeaks.

We see that the reasoning of the argument is basically the following: Since Croton's jays always migrate south with crookbeaks and thus do not ever migrate south on their own, Croton's jays must not have the navigational ability to migrate on their own.

Which of the following, if true, most strengthens the argument above?

This is a Strengthen question, and the correct answer will help to confirm the conclusion.

(A) Croton's jays lay their eggs in the nests of crookbeaks, which breed upon completing their southern migration.

This choice weakens, rather than strengthens, the argument.

After all, if this choice is true, then there's an alternative possible reason why Croton's jays migrate with crookbeaks.

It could be that, rather than migrate with crookbeaks because of a lack of navigational abilities, jays migrate with crookbeaks to be with them when they build nests and breed in order to lay eggs in the nests of crookbeaks.

Eliminate.

(B) The three species most closely related to crookbeaks do not migrate at all.

That fact that some species do not migrate doesn't indicate anything about jays' navigational abilities.

Eliminate.

(C) In the spring, Croton's jays migrate north in the company of Tattersall warblers.

This choice is interesting.

We already know that Croton's jays migrate south with crookbeaks.

Now, this choice tells us that, not only do jays migrate south with another species, they also migrate north with another species Tattersall warblers.

So, this choice helps to confirm that conclusion by confirming that, whenever jays migrate, they do so with another species.

For what it's worth, it also interesting that jays migrate with another species when they migrate north. That information tends to indicate that jays aren't migrating with crookbeaks just because they like their company. Apparently, jays are willing to join different species as long as the other species is going in the right direction. So, it's a reason to believe that they migrate with another species because they lack the ability to navigate on their own.

So, this choice helps to confirm the conclusion.

Keep.

(D) Species other than Croton's jays occasionally accompany flocks of migrating crookbeaks.

The fact that other species occasionally migrate with crookbeaks doesn't indicate that jays lack navigational abilities.

If anything, this information indicates that it may be that some other species don't have navigational abilities because they too migrate with crookbeaks.

In any case, this choice basically indicates the same thing about other species that we already know about jays, that they migrate with crookbeaks, but it doesn't provide new information confirming that any species does so because of a lack of navigational abilities.

Eliminate.

(E) In the spring, crookbeaks migrate north before Croton's jays do.

This choice weakens, rather than strengthens, the argument.

After all, if Croton's jays don't migrate north with crookbeaks in the spring, then it could be that jays have a reason other than a lack of navigational abilities for migrating south with crookbeaks in the fall.

After all, migrating north presumably requires navigational abilities as well. So, if jays migrate north without crookbeaks, then it could be that something else is going on.

Eliminate.

Correct answer: C
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