Question 96·Hard·Inferences
Wind turbines are often criticized for causing bird fatalities, particularly among raptors that collide with the rotating blades. Yet ecologist Nadine Culver’s multi-year survey of grassland preserves in the American Midwest revealed a more complicated picture. On preserves with turbines, collisions did kill an average of five percent of the local red-tailed hawk population annually. However, the turbines’ tall towers also generated consistent, turbine-induced updrafts that the hawks exploited to soar with less energy expenditure. This energy savings allowed adult hawks to expand their hunting ranges and provision nestlings more efficiently, resulting in higher fledgling survival than on turbine-free preserves. Culver concludes that the net effect of turbines on hawk populations can be either negative or positive, depending on site-specific factors such as prey abundance and tower placement, indicating that the presence of wind turbines _____.
Which choice most logically completes the text?
For SAT "complete the text" inference questions, focus on the sentence that sets up the blank (especially phrases like "concludes" or "indicating that"). Paraphrase that sentence, keeping any qualifiers (for example, "can be either" and "depending on"). Then pick the option that matches both the direction/claim and the qualifications, and eliminate answers that make the conclusion one-sided (only positive/only negative), add unsupported generalizations ("usually"), or narrow the cause to fewer factors than the passage provides.
Hints
Focus on the scientist’s conclusion
Reread the last sentence beginning with "Culver concludes" and pay attention to how she describes the overall, or net, effect of turbines on hawk populations.
Put the key sentence into your own words
Restate "the net effect ... can be either negative or positive, depending on site-specific factors" in simpler terms. Your answer should keep both ideas: two possible outcomes and dependence on local conditions.
Watch out for one-sided or overly narrow choices
As you check the choices, be skeptical of answers that claim turbines usually hurt, usually help, or that the outcome depends on only one factor (when the passage mentions multiple).
Step-by-step Explanation
Locate the key part of the passage
Focus on the final sentence, especially the conclusion: "Culver concludes that the net effect of turbines on hawk populations can be either negative or positive, depending on site-specific factors such as prey abundance and tower placement." The correct ending must closely match this idea.
Paraphrase the scientist’s conclusion
Restate the conclusion: wind turbines can sometimes reduce hawk populations (through collisions) and can sometimes support them (through energy-saving updrafts that improve provisioning and fledgling survival). Which outcome occurs depends on preserve-specific conditions (for example, prey abundance and turbine placement).
Eliminate choices that distort the conclusion
Compare each option to the paraphrase:
- Eliminate any choice that says the effect is always negative, since Culver says it can be negative or positive.
- Eliminate any choice that claims turbines are generally/usually beneficial, since the passage does not say benefits outweigh costs in most places.
- Eliminate any choice that narrows the dependence to only one factor (for example, prey alone), since Culver cites multiple site-specific factors (including tower placement).
Choose the option that matches both parts of the conclusion
"May lead to population declines or gains for hawks, contingent on conditions unique to each preserve" matches both key ideas: the net effect can go in either direction (declines or gains) and it depends on site-specific conditions. Therefore, this is the correct answer.