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Question

Difficulty: MediumDistinguishing Claims from Evidence

Passage

For years, ornithologists suspected that artificial light at night (ALAN) disrupted the navigation of migratory songbirds, but the precise mechanism remained elusive. A recent study of blackcaps (Sylvia atricapilla) passing through urban corridors offers a clearer picture. The researchers hypothesized that artificial illumination disorients birds by interfering with their magnetic compass, which is mediated by light-sensitive proteins in their eyes. To test this, they monitored the birds in controlled orientation cages under varying light conditions. Under natural starlight, the birds oriented consistently toward their migratory direction. However, when exposed to low-intensity blue-filtered artificial light, their orientation became scattered, and under bright white LED light, they failed to establish any migratory direction at all. The researchers concluded that the presence of artificial light at night actively impairs the physiological mechanisms responsible for avian navigation. Critics argue that the disorientation observed in cages might not reflect wild behavior, pointing to tracking data showing that some wild songbirds successfully navigate urban areas. Nevertheless, the study's findings demonstrate that artificial light directly disrupts the internal compass of captive birds, suggesting that urban light pollution poses a significant threat to migratory species.

Based on the passage, which of the following statements represents a claim made by the researchers rather than the evidence used to support it?

  1. A
    The orientation of the birds became scattered when they were exposed to low-intensity blue-filtered light.
  2. B
    The birds oriented consistently toward their migratory direction under natural starlight.
  3. Artificial light at night actively impairs the physiological mechanisms responsible for avian navigation.Answer
  4. D
    The birds failed to establish any migratory direction when exposed to bright white LED light.

Answer

The statement asserting that artificial light at night actively impairs the physiological mechanisms responsible for avian navigation.
The statement asserting that artificial light at night actively impairs the physiological mechanisms responsible for avian navigation represents a claim because it is a generalized conclusion and interpretive hypothesis proposed by the researchers. It cannot be directly observed without synthesizing the specific data points collected in the experiment.

Step-by-Step Solution

1
Identify the researchers' primary hypothesis and ultimate conclusion in the passage.
The researchers concluded that artificial light at night (ALAN) actively impairs the physiological mechanisms responsible for avian navigation, which is a generalized claim requiring evidence.
Differentiating between the overarching claim (the conclusion) and the raw data points is necessary to separate claims from evidence.
2
Examine the remaining statements to determine if they represent data points or observations.
The statements describing bird orientation under natural starlight, blue-filtered light, and bright white LED light represent specific, observable results of the experiment.
Observational results obtained during an experiment function as evidence used to support or refute a hypothesis.
3
Match the identified claim to the options to select the correct answer.
The option regarding the impairment of physiological mechanisms is the claim, while the others are evidence.
This directly addresses the question's requirement to identify the claim rather than the evidence.

Key Concept

Distinguishing Claims from Evidence
Estimated Time:1m 30s
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Distinguishing Claims from Evidence

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