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The red-eyed cowbird

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The red-eyed cowbird

by vivek1110 » Mon May 03, 2010 8:52 am
The red-eyed cowbird breeds by parasitizing the nests of orioles, among other birds. The cowbird lays its eggs in the orioles' nests while the female orioles are out searching for food. The cowbird has evolved certain traits and behaviors to ensure the success of its deception: It throws one oriole egg out of the nest for every one of its own eggs that it lays therein, and it has evolved an egg coloration similar to that of the oriole. An oriole whose nest has thus been parasitized will subsequently incubate and rear the cowbird chick, unaware of the cowbird's ploy.

Which of the following conclusions can most properly be drawn from the information above?

A The stability of oriole populations is threatened by the behavior of red-eyed cowbirds.
B The oriole does not possess any numeric ability.
C The stability of red-eyed cowbird populations depends on the proximity of nesting orioles.
D The red-eyed cowbird's behavior is not learned.
E Scientists are unable to distinguish between a red-eyed cowbird egg and an oriole egg based solely on visual examination.


OA soon.
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by gsinghal » Mon May 03, 2010 9:17 am
I am confused between A and D......

but the passage does not states that Oriole is the only bird whose nest Cowbird parasites...The red-eyed cowbird breeds by parasitizing the nests of orioles, among other birds.

Also I chose D because the passage says The cowbird has evolved certain traits and behaviors.

IMO D
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by analyst218 » Mon May 03, 2010 3:47 pm
vivek1110 wrote:The red-eyed cowbird breeds by parasitizing the nests of orioles, among other birds. The cowbird lays its eggs in the orioles' nests while the female orioles are out searching for food. The cowbird has evolved certain traits and behaviors to ensure the success of its deception: It throws one oriole egg out of the nest for every one of its own eggs that it lays therein, and it has evolved an egg coloration similar to that of the oriole. An oriole whose nest has thus been parasitized will subsequently incubate and rear the cowbird chick, unaware of the cowbird's ploy.

Which of the following conclusions can most properly be drawn from the information above?

A The stability of oriole populations is threatened by the behavior of red-eyed cowbirds.
B The oriole does not possess any numeric ability.
C The stability of red-eyed cowbird populations depends on the proximity of nesting orioles.
D The red-eyed cowbird's behavior is not learned.
E Scientists are unable to distinguish between a red-eyed cowbird egg and an oriole egg based solely on visual examination.


OA soon.
A i think. THe passage implies that oriole will keep on raising cowbird chicks while oriole chicks keep on dying.
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by vivek1110 » Mon May 03, 2010 4:32 pm
[spoiler]OA: D[/spoiler]
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by paddle_sweep » Tue May 04, 2010 1:58 am
What's the problem with 'C'?

Also,what does 'not learned' mean in 'D'?
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by debmalya_dutta » Tue May 04, 2010 4:08 am
I do not understand what is wrong with A which is what I selected
A The stability of oriole populations is threatened by the behavior of red-eyed cowbirds. - Passage clearly states "The cowbird has evolved certain traits and behaviors to ensure the success of its deception: It throws one oriole egg out of the nest for every one of its own eggs that it lays therein, and it has evolved an egg coloration similar to that of the oriole". This means that as the cowbirds incubate more eggs by behaving as parasites , they will also destroy more of oriole eggs and hence the oriole population is in danger

Option D on the other hand - "The red-eyed cowbird's behavior is not learned. "The cowbird has evolved certain traits and behaviors to ensure the success of its deception" . It means that even though its behavior may continue to evolve , we do know about its current tactics
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by stephen@knewton » Tue May 04, 2010 4:37 am
Some great questions raised in this thread. I think it will help to recall two things about a "conclusion" question, which is very similar to an inference question. First, remember what our task is: we must pick and answer choice that MUST be true based upon the evidence that's presented in the stimulus. Second, recall the common wrong answer choices: these will be statements that MIGHT be true, and statements that CAN'T be true. The former can be the most deceptive, and both (A) and (C) are of this type.

A tip for this question type: often the correct answer comes directly from ONE specific statement made in the stimulus, and is narrower in scope than one expects. Don't be put off by an answer choice that is very limited in scope; that's often the best one!

Looking at our choices:

A) As a few posters have noted, this sounds completely reasonable! If cowbirds are tossing out oriole eggs, it may well be true that they are threatening the oriole population in the process. But we can't KNOW this! It may be that orioles lay enough eggs to accommodate the actions of cowbirds and still maintain stable population levels. We are not given enough evidence to know that this MUST be true, so it can't be the correct answer.

B) This one is easier to eliminate. If anything, the cowbird's egg-tossing suggests an expectation that the oriole CAN count!

C) Like the first answer choice, this one seems reasonable and COULD be true! We are told that cowbirds use oriole nests to reproduce, but we're never told anything about proximity. Perhaps the cowbird flies a great distance to lay these eggs. Because we can't KNOW that this is true, it can't be the right answer choice.

D) This answer is correct. It is deceptively specific to ONE piece of evidence and hides beneath a bit of tricky vocabulary. We are told that the cowbird's behavior has evolved, which means that it's driven by instinct, and so it cannot entirely have been learned ... these terms refer to different ways that a behavior can originate.

E) This choice is also easier to eliminate. We are told that the cowbird's visual trickery can fool orioles; we are told nothing about whether it can fool a human scientist (and let's assume the GMAT does not believe in little orioles wearing lab coats).

So to recap the strategy here, the incorrect but tempting answer choices (A and C) both COULD be true, but the correct choice (D) MUST be true, based on one very specific statement that's made in the stimulus. Hope that helps!

Steve P.
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by paddle_sweep » Tue May 04, 2010 6:20 am
Thanks Steve. That was a great explanation.

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