Every fall Croton's jays migrate south. The jays always join flocks of

Before does not signify whether they are in the vision of CJ's to follow.

If they migrate a month before, CJ cannot see the CB, unless CB moves an inch a day.

if they migrate 10 min before, CJ possibly can see CB in the air and follow them for navigation.

Also the Q is clearly about moving together. not before/behind.

I narrowed it down to C and D, and picked C based on the assumption that the jays always need someone to migrate with, hence,

Conclusion: The jays can't navigate south on their own.
Evidence: Share migration with crookbeaks, if jay is lost :: jay finds crookbeaks
Assumption: The jays always migrate with birds of a differing species.

Not sure if this is entirely the correct reasoning...guess I would've been a little lucky.

Here's the explanation:

The conclusion of the given argument is that 'Croton's jays lack the navigational ability to find their way south on their own'. The question asks us to strengthen the argument and hence this conclusion. Which of the given options would prove that the Croton's jays, indeed lack the navigational ability to find their way (south, north or any other direction)?

Option C clearly supports our conclusion by stating that the Croton's jays migrate north in the company of Tattersall warblers and it has already been given in the premise that Croton's jays always join flocks of migrating crookbeaks to travel south. Hence this option, along with the given premise supports the conclusion that Croton's jays indeed lack the navigational ability to find their way.

The other four options are clearly out of scope of the given argument.

Hope this helps.

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.

Which of the following, if true, most strengthens the argument above?
A. Croton's jays lay their eggs in the nests of crookbeaks, which breed upon completing their southern migration.
Out of scope
B. The three species most closely related to crookbeaks do not migrate at all.
out of scope
C. In the spring, Croton's jays migrate north in the company of Tattersall warblers.
Correct choice that strenthens the conclusion of the argument that says that Croton's jays lack navigational ability.
D. Species other than Croton's jays occasionally accompany flocks of migrating crookbeaks.
Out of scope
E. In the spring, crookbeaks migrate north before Croton's jays do.
weakens the argument

Really, none of the answers here are good. This is a horrific question. I picked A because it seemed somewhat relatable to the fact that the CB's cannot migrate south on their own, and after reading it, I can see why A is out of scope, but still: it is asking about migrating south, therefore how does CB's going with someone in the north strengthen it? I can think of a million CR questions where I have seen these types of answer choices (i.e., conclusion asks for south and answer is north) and it is incorrect. This is bad by the GMAT -- is this how they're going to make us struggle for a high score?!

Hello, Nandini21. In an effort to assist you and the larger community, I will provide a full analysis of the question. Since we are looking to strengthen the argument, we have to keep an eye on just what that argument says. The passage:


This seems a fitting passage for the beginning of fall (in the northern hemisphere), when a lot of birds begin their annual southward migrations. Anyway, notice the extreme language in the second line: the [Croton's jays] always join flocks of migrating crookbeaks (my italics). The third sentence follows up on this absolute truth within a conditional: even if a jay cannot keep up with the flock of crookbeaks, it wanders until it comes across another flock. Then, we get the conclusion, which you have identified above: Croton's jays lack the navigational ability to find their way south on their own.

To strengthen this assertion, we need to find an answer choice that addresses at least one of two angles:

1) Croton's jays cannot migrate (at all) on their own;

2) Croton's jays cannot migrate south on their own.

What do the answer choices have in store for us?


Although there is some information about a southern migration at the tail-end of the answer choice, we are not concerned with what happens after the migration. This information about Croton's jays being parasitic nesters has nothing to do with their migratory habits. This should be an easy elimination.


For the uninitiated, this answer choice might sound reasonable—if crookbeak-like birds do not migrate, then the jays must be following the crookbeaks, so the thinking may go—but the argument itself is not based on the migratory habits of any bird other than Croton's jays. We are not concerned with relatives of crookbeaks.


Now, I agree that it can be off-putting to see north in the answer choice when the argument is based on the jays migrating south. But remember what we outlined above. Perhaps the direction is less important than the overarching point that Croton's jays cannot migrate unaccompanied by other birds. We cannot ignore that this answer choice lays out just such a scenario, in which the jays are riding the coattails of the warblers to make their way to a different location. If the direction bothers you—and I will admit that it gave me pause—then simply place this option on hold while you assess the others.


First off, the argument is not based on birds besides Croton's jays, so these other birds fall outside the scope of the argument. I extended the red text, however, to point out another common problem that pops up in incorrect answer choices: vague, unqualified language. The word occasionally here acts in the capacity of a sometimes or a some in a different question, and unless the argument is based on an absolute condition (e.g., something always or never happens), this sort of vague language will not affect the argument one way or the other. Think about it: if something occasionally occurs, then we could just as easily say that that event sometimes does not occur. All of this is to say that you need to watch for unqualified language. It may not be the most apparent target here, but it may very well be in another question.


Notice the direction: north. The argument, of course, is based on the jays flying southward with the crookbeaks. Just because the crookbeaks flock north ahead of the jays does not mean the jays could not hitch a ride with the crookbeaks on their way south at the end of the season. Unfortunately, we are unable with the information in this answer choice to supply any explanation as to how Croton's jays migrate northward. Is it by making their own way (a fact that would fly in the face of the argument), or by finding some other bird to follow? Without any information to lean on, we cannot say that (E) strengthens the argument, so we need to abandon it.

There you have it. Of the five answer choices presented, a single one provides information that the Croton's jays migrate in the company of other birds, thereby strengthening the notion that the jays may lack the navigational ability to find their way... on their own. That is why we need to choose (C).

I hope my explanation proves useful. Good luck with your studies.

- Andrew

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

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.)


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]?


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

Wouldn't E indicate that CJs follow CB up north?

Since I'm not a native speaker, I really can't understand the latter part in A "which breed upon completing their southern migration." what does this mean? Appreciated if anyone care to help!!

It means they reproduce after they have completed their journey. i.e have sex and give birth

So C seems to be the best available option!

Option C never says about south and is not a good contender for answer. It does not give thought whether Jays cannot travel to south with out help.

Option E says Crookbeaks travel with out Jays, means Jays may or may not require some one to take them to North but they require some one to take to South.

Not able to understand how Option C is better than Option E.

Crotons (Lack the navigational ability) ---------follow ------> Crookbeaks

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

If crookbeaks migrate before Crotons , we cannot state whether Croton will reach their destination/not, hence this doesn't strengthen the conclusion...

To strengthen the conclusion " Croton's jays lack the navigational ability to find their way south on their own." we need a statement to show that the Crotons are dependent on the crookbeaks for navigation/migration and only (C) does it perfectly.

To prove : Croton's jays lack the navigational ability to find their way south on their own.

As mentioned in the passage, Croton's jay is dependent on crookbeaks for migration to south.
If we are able to find some clue which suggests that the Croton's jay needs the same kind of help in migration, then that will help to strengthen the argument.
option (C) suggests the same.

Ans : C

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

I narrowed it down to (C) and (E) and chose E because "migrate north in the company" shows that the Crotons migrate together with another species, indicating they may not necessarily be able to navigate themselves.

(E) In the spring, crookbeaks migrate north before Croton's jays do.
Versus (E), I initially interpreted that the Crotons follow the Crookbeaks after they migrate, BUT that is a massive assumption as "migrate" is a synonym for journey. So if Crotons follow the Crookbeaks AFTER they migrate, then it means they are travelling alone and thus able to navigate. This is a 180 degree option. I.e. it Weakens the Conclusion.

Totally agree, this is one of those questions where we have to mark the answer which feels the least wrong.
I marked (A) as well with the same reasoning, marking (C) is like using transitive property which doesn't really translate well in CR questions.

C gives another reason to beleive that they don't have navigational ability. Hence the answer