Question 122·Medium·Inferences
To examine whether artificial light at night alters the paths of nocturnal songbird migrations, Dr. Elena Alvarez analyzed 20 years of springtime weather-radar data from a large city and a nearby rural sector. On overcast nights, the city consistently showed higher migration passage rates than the rural sector; on clear nights, rates were similar between areas. During a week-long citywide light-dimming initiative, the over-city excess on overcast nights diminished, while rural rates were unchanged. Alvarez therefore concluded that ______
Which choice most logically completes the text?
For SAT “scientist concluded that” questions, first restate the study’s main question in your own words, then list the key findings as simple comparisons (e.g., city vs. rural, clear vs. cloudy, before vs. during intervention). Look for the answer that directly explains those patterns without adding new scientific claims or making broader generalizations than the data allow. Reject choices that change the subject (e.g., from where something happens to how much happens) or introduce causes and mechanisms not mentioned in the passage.
Hints
Focus on the contrast between nights
Pay close attention to how migration rates differ between overcast and clear nights for the city versus the rural sector. What is different, and when is it different?
Use the light-dimming week as a clue
Ask yourself: When the city dims its lights, what changes in the migration data, and what stays the same? What does that suggest about the role of city lighting?
Check for overgeneralizations or new information
Eliminate answer choices that (1) make claims about the entire region or total migration numbers the study never measures, or (2) introduce ideas (like how birds navigate) that are not mentioned in the passage.
Step-by-step Explanation
Clarify the research question
The question describes Dr. Alvarez’s study and then says, “Alvarez therefore concluded that ______.” You are being asked: based on the data given, what conclusion about migration and artificial light at night is most logical?
So first, identify: she is testing whether artificial light at night changes the paths of migrating songbirds.
Summarize the key patterns in the data
Pull out the main results:
- On overcast nights, the city has higher migration passage rates than the rural sector.
- On clear nights, migration rates are similar between city and rural.
- During a light-dimming week in the city, the extra migration over the city on overcast nights shrinks, but rural rates stay the same.
So, the difference between city and rural shows up only on cloudy nights and becomes smaller when the city’s lights are dimmed.
Interpret what the light-dimming week tells you
The light-dimming initiative changes only the city’s lighting, not the weather or the rural area. During that week:
- The “over-city excess” on cloudy nights gets smaller.
- Rural migration rates do not change.
This strongly suggests that it is something about the city itself, and specifically its nighttime lighting, that creates the extra migration over the city on cloudy nights. It does not show that clouds reduce overall migration, nor that fewer birds are migrating in total.
Match the conclusion to the evidence
The best conclusion must:
- Connect city lighting to where birds are flying.
- Fit the fact that the effect appears on cloudy (overcast) nights but not clear nights.
- Be supported by the light-dimming week, where reducing city light reduces the city’s extra migration without changing rural rates.
The only choice that matches all of this is: “urban lighting likely draws migrating songbirds toward the city on cloudy nights.” (Choice D).