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Based on the text, what accounts for the smaller shift toward higher song frequencies observed among sparrows in heavil…

Urban noise consists predominantly of low-frequency rumble from traffic, which can mask bird vocalizations. To maintain communication, some songbirds increase the minimum frequency of their songs. However, acoustic transmission involves trade-offs: higher-frequency sounds have shorter wavelengths that attenuate rapidly when scattered by dense foliage and tree trunks, whereas lower-frequency sounds bend around such physical obstacles with minimal signal degradation. When ecologist Julia Garcés and colleagues examined song sparrows (<em>Melospiza melodia</em>) inhabiting noisy urban environments, they found that while sparrows in open, paved plazas elevated their song frequencies substantially, those in heavily wooded urban parks exhibited far smaller upward shifts despite facing equivalent traffic noise levels.

Based on the text, what accounts for the smaller shift toward higher song frequencies observed among sparrows in heavily wooded parks compared to those in open plazas?

Answer & explanation

Correct answer: A. The signal loss that higher-frequency sounds experience around dense vegetation offsets the benefit of shifting frequencies to avoid traffic noise.

According to the passage, urban sparrows shift to higher frequencies to avoid having their songs masked by low-frequency traffic noise. However, this shift entails an acoustic trade-off: higher-frequency sounds attenuate quickly when scattered by physical obstacles such as tree trunks and foliage, whereas lower-frequency sounds bend around these obstacles with minimal degradation. Because wooded parks contain dense foliage and trunks, sparrows in those habitats would suffer significant signal loss if they sang at higher frequencies, diminishing the advantage gained from avoiding traffic noise. In open plazas, the absence of these vegetative obstacles allows sparrows to elevate their frequencies without incurring the same transmission penalty, making Choice A correct.

Choice B fails because it contradicts the text, which explicitly notes that sparrows in the wooded parks faced "equivalent traffic noise levels" rather than muffled noise.

Choice C fails because it inverts the acoustic mechanism described in the passage; lower frequencies bend around obstacles with minimal degradation rather than suffering greater degradation.

Choice D fails because it introduces an unsupported factor (differences in sound reflection between paving materials and vegetation) that is never mentioned or implied in the text.

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Based on the text, what accounts for the smaller shift toward higher song frequencies observed among sparrows in heavil…

Based on the text, what accounts for the smaller shift toward higher song frequencies observed among sparrows in heavily wooded parks compared to those in open plazas?

Answer & explanation

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