The song of the yellow warbler signals to other yellow warblers that a

EXPLANATION FROM POWER PREP

Due to the verbose nature of stimulus, it is important to isolate the essential elements that form the structure of the argument:

Premise: Yellow warblers sing special songs when molting.

Premise: The special song deters other yellow warblers from encroaching upon the territory of the molting warbler.

Conclusion: A molting warbler has no competition for food within its territory.

Because this is an assumption question, the answer you select must contain a statement upon which the argument depends, i.e. a statement that is necessary for the conclusion to be true. All we know from the premises is that other warblers will not enter the territory of the singer: that alone does not preclude other birds from competing with the singing warbler for food.

Typically, if you see a major weakness in the argument, look for a Defender assumption answer stating that the particular weakness does not exist. In other words, the author must be assuming that no birds other than yellow warblers will compete with the molting warbler for food in its area. This prephrase reveals answer choice (C) to be correct.

Answer choice (A): Whether the core area contains enough food to sustain the molting warbler is irrelevant to the conclusion, which is about whether the warbler faces any competition for the food supply within that area.

Answer choice (B): Whether or not other molting birds can lay claim to the feeding territory of the singer is irrelevant to determining whether the singer would face competition for food in that area.

Answer choice (C): This is the correct answer choice, as it agrees with our prephrase. If this answer is troubling you, use the Assumption Negation Technique and ask yourself if the following statement would undermine the argument:

There are birds other than yellow warblers that compete with yellow warblers for food.

This clearly shows that the author’s conclusion is flawed and weakens her argument. Therefore, answer choice (C) is an assumption upon which the argument depends.

Answer choice (D): This answer choice may seem attractive, because it supports the idea that yellow warblers would face no competition for food in their feeding area: the other kinds of birds simply do not eat the same kinds of food as warblers do. Although this statement supports the conclusion of the argument, it is not necessary for the conclusion to be true. Even if the other birds ate the same kinds of food as warblers do, that does not prove that warblers would face competition in their feeding area, and therefore does not weaken the conclusion of the argument.

Answer choice (E): The relative size of the core areas of each warbler’s feeding territory has no bearing on whether warblers face competition for food. This answer choice falls outside the scope of the argument and is therefore incorrect.