An inference question about a study tests what its comparisons and follow-up test show. Read what the researcher tested, then name each place and its results under each condition. Ask what changed in the follow-up, and what stayed the same. Use that change to test a possible cause, and predict the smallest conclusion the results support. Keep the conclusion tied to the tested condition, since a result in one setting doesn't show the same effect everywhere.
Hints
- Hint 1
Compare the city and rural rates under each sky condition. When do the two areas differ?
- Hint 2
Track what changed during the light-dimming initiative. Read the city and rural results separately.
- Hint 3
How does changing the city's lighting help you explain the earlier city-versus-rural difference on overcast nights?
Step-by-step
Compare places, then use the dimming test
Step 1Find when the areas differ
On overcast nights, migration passage rates were higher over the city than over the rural sector, but on clear nights, rates were similar between areas. When does the difference appear? Only under cloudy skies, so the conclusion needs to explain a difference tied to one sky condition, not a pattern found on every night.
- Step 2
Track the dimming result
The dimming week compares normal city lighting with dimmer city lighting. What changed in the results? During a week-long citywide light-dimming initiative, the over-city excess on overcast nights diminished, while rural rates were unchanged. In other words, the city's extra bird traffic shrank without a matching rural change.
- Step 3
Say what the change can show
Can clouds alone explain why the city's excess shrank? The text reports the dimming results on overcast nights, so lighting changed while the sky condition stayed the same. The unchanged rural rate also gives us no sign of a drop across the whole region. The evidence links lighting to the city's extra bird traffic, but it doesn't show that the total number of migrating birds fell.
- Step 4
Choose the limited conclusion
The choice with urban lighting likely draws answers whether light alters the paths of nocturnal songbird migrations: it says the lights attract birds toward the city. The words on cloudy nights limit the claim to cloudy nights, and likely leaves room for uncertainty. Choice B.