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Difficulty: MediumWeaken

Ornithologist: Urban song sparrows consistently sing at higher minimum audio frequencies than rural sparrows. Researchers originally attributed this difference to ambient traffic noise, claiming that birds elevate their pitch to prevent low-frequency engine rumbles from masking their songs. However, in enclosed urban nature reserves where dense perimeter soundwalls effectively eliminate all city traffic noise, resident song sparrows nevertheless vocalize at the same elevated pitch as those living beside major highways. Thus, urban traffic noise is not the main reason urban sparrows sing at higher frequencies.

Which one of the following, if true, most seriously weakens the ornithologist's argument?

  1. A
    Rural song sparrows translocated into loud urban centers fail to raise their vocal frequencies as quickly or effectively as sparrows native to the city.
  2. Song sparrows learn their permanent vocal repertoire as juveniles in roadside nesting territories before dispersing into quieter urban reserves.Answer
  3. C
    Urban sparrows possess narrower beaks adapted for eating ornamental garden seeds, a physical trait that naturally produces higher-pitched vocalizations in quiet environments.
  4. D
    Perimeter soundwalls in urban nature reserves fail to block high-frequency sounds produced by nearby industrial construction.
  5. E
    Female song sparrows in quiet urban reserves always prefer mates whose songs are higher in frequency than the average songs heard in rural populations.

Answer

Song sparrows learn their permanent vocal repertoire as juveniles in roadside nesting territories before dispersing into quieter urban reserves.
The correct response undermines the conclusion by providing a developmental mechanism linking traffic noise directly to the songs of birds in quiet reserves. If sparrows develop their lifelong songs while nesting as juveniles near noisy roads and subsequently move into quiet reserves as adults, traffic noise remains the primary causal factor driving their high-frequency vocalizations despite their current quiet surroundings.

Step-by-Step Solution

1
Identify the conclusion and supporting premises of the argument.
Conclusion: Traffic noise is not the main driver of higher singing frequencies in urban sparrows. Premise: Sparrows residing in quiet, sound-shielded urban reserves still sing at the same elevated frequencies as highway sparrows.
Weaken questions require isolating the logical leap between the evidence and the main claim.
2
Identify the core assumption bridging the premise to the conclusion.
The ornithologist assumes that if current adult birds in quiet reserves sing at high frequencies, traffic noise cannot have caused their behavior.
The author overlooks the possibility of a delayed, developmental, or learned effect from earlier noise exposure.
3
Evaluate the choices to find new information that bridges the quiet reserve observation with traffic noise causality.
The statement explaining that sparrows acquire their song repertoire as juveniles along noisy roads before moving into quiet reserves explains why quiet-reserve birds still exhibit noise-induced vocal shifts.
This preserves traffic noise as the primary cause while accounting for the author's observed counterexample.

Key Concept

Causal reasoning and developmental lag counterexamples
Estimated Time:1m 15s
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