Ecologist: Before finding a mate, male starlings decorate their nests with fragments of aromatic plants rich in compo...

First on November 27 at 02:48PM

caged females?

Im confused why D is correct. It says nothing about "caged" females. So how can we assume that is the correct answer? We are told the answers are in the passage given to us, but then we come upon questions like this, and that is definitely not in the passage.

1 Reply

Irina on November 27 at 05:27PM

@madisanbryant,

This is a strengthen question, thus the correct answer choice would be a new piece of information that strengthens the argument. As opposed to inference/ must be true questions, weaken/ strengthen questions are among question types that introduce new information.

Let's look at the argument. The argument tells us that male starlings decorate their nests with plants known to kill insects harmful to nestlings. Some researchers hypothesize that it is done for nesting protection, but based on the evidence that males cease to use these plants once egg-laying starts, the argument concludes that the decorations function to attract females.

Let's look at the answer choices:

(A) Adult starlings are able to defend themselves against parasitic insects.

Incorrect. This fact has no impact on the conclusion, the argument is about nestlings, not adult birds.

(B) Male starlings do not decorate their nests with unusually small populations of parasitic insects.

Incorrect. This fact is also irrelevant, the argument is about the function of decoration in cases when they do decorate the nests.

(C) Nestlings grow faster in nests that incorporate aromatic plants.

Incorrect. The argument is about specific plants that are rich in insect killing compounds, not just any aromatic plants, thus this fact has no impact on the conclusion. If we were to assume that this fact refers to plants in the stimulus, this fact would weaken the argument as it would suggest an alternative function rather than attracting females.

(D) Male starlings tend to decorate their nests with a greater number of aromatic plants when a caged female is positioned adjacent to the nest.

Correct. This fact demonstrates a cause-effect relationship between nest decoration and female presence. (D) points out that when a female bird is nearby but cannot get to the male bird since it is caged, the male bird tries harder to make the nest more attractive by incorporating more plants.

(E) The compounds in the aromatic plants used by the male starlings to decorate their nests are harmless to nestlings.

Incorrect. This fact has no impact on the conclusion because it fails to add any explanation as to the main function of such decorations.

Let me know if you have any other questions.