Question 146·200 Super-Hard SAT Reading Questions·Information and Ideas
At three marshes, wildlife managers credited a sharp increase in black tern numbers to a program removing invasive mink. The increase began the year after trapping started. During the same period, however, managers also raised spring water levels at those marshes; nearby comparison marshes received neither intervention. Tern numbers increased only at the managed marshes. Nest records show that hatching success began improving several weeks before managers raised the water levels, but demographic estimates indicate that higher adult survival, not hatching success, accounted for most of the increase in tern numbers. In addition, managers had selected the three marshes partly because each contained recently restored nesting islands, which the comparison marshes lacked. Taken together, these findings suggest that _____
Which choice most logically completes the text?
For a difficult inference question, track the timing of events, distinguish among different measured outcomes, and determine whether a comparison isolates a single factor. Choose the conclusion that incorporates all relevant evidence without treating a possible explanation or confounding factor as a proven cause.
Hints
Use the sequence of events
Identify which change occurred only after hatching success had already begun improving.
Separate the measured outcomes
Consider whether the factor associated with improved hatching necessarily explains the change in total tern numbers.
Assess the comparison marshes
Determine whether the managed and comparison marshes differed in only one relevant respect.
Step-by-step Explanation
Interpret the timing evidence
Hatching success began improving before managers raised the water levels. Therefore, the higher water levels cannot readily explain the initial improvement in hatching.
Distinguish hatching from population growth
The passage states that higher adult survival, rather than improved hatching success, accounted for most of the increase in tern numbers. Evidence about the timing of hatching therefore does not by itself identify the cause of the overall population increase.
Evaluate the comparison
The managed marshes differed from the comparison marshes in several ways: they received both mink removal and higher water levels, and they already contained restored nesting islands. Because these factors were not separated, the comparison cannot isolate the effect of mink removal.
Draw a qualified inference
The findings weaken one specific explanation—raised water levels causing the early improvement in hatching—but do not establish that mink removal caused the broader population increase.