Question 102·Hard·Inferences
In a 2023 study, ornithologist Lydia Klimczak and colleagues examined satellite-tracking data from 148 sand martin (Riparia riparia) individuals collected between 1980 and 2020. They found that
- the birds’ departure dates from their sub-Saharan wintering grounds remained essentially constant over the 40-year interval,
- average air temperatures at those wintering grounds also showed no consistent trend,
- mean spring temperatures at several key stopover wetlands along the birds’ migration corridor through North Africa and southern Europe rose by roughly , and
- the total time spent resting at those stopovers declined by about 30 percent. As a result, sand martins reached their European breeding sites roughly seven days earlier in 2020 than in 1980. From these findings, Klimczak and colleagues inferred that over the study period, ______.
Which choice most logically completes the text?
For inference questions like this, first restate in your own words what the passage explicitly says changed over time and what stayed the same. Then identify the outcome that needs explaining (here, earlier arrival) and link it only to factors the passage actually connects to that outcome. Eliminate choices that contradict stated facts (like “departure dates stayed constant”) or that assert a specific cause (like a new route or earlier departure) that the passage does not establish. Choose the option that most directly and conservatively explains the result using only the given evidence.
Hints
Focus on what changed vs. what stayed the same
List which variables the study says remained constant and which ones changed over the 40 years. Then ask: which of these changes could logically explain earlier arrival in Europe?
Pay attention to locations: wintering grounds vs. stopovers
Notice the difference between the African wintering grounds and the North Africa/southern Europe stopover wetlands. Where did temperatures change, and where did they not?
Watch out for new, unsupported ideas
Check whether each answer choice is directly supported by the findings or whether it introduces something the passage doesn’t establish (for example, a different route, different departure timing, or unrelated factors).
Link the time-resting change to the arrival change
The birds are arriving earlier but not leaving earlier. How could decreasing total time spent resting during migration contribute to this difference in arrival time?
Step-by-step Explanation
Understand what the question is asking
The question asks what Klimczak and colleagues inferred from their findings. That means you must choose the statement that logically follows from the data described, without adding unsupported ideas.
Summarize the key findings
List what the study found:
- Departure dates from sub-Saharan wintering grounds: essentially constant.
- Average air temperatures at wintering grounds: no consistent trend.
- Mean spring temperatures at key stopover wetlands: rose by about .
- Total time resting at stopovers: declined by about 30%.
- Result: birds reached European breeding sites about seven days earlier in 2020 than in 1980.
So, what changed over time? Temperatures at stopovers and time spent resting at those stopovers. What did not change? Departure dates and temperatures at the wintering grounds.
Connect the changing factors to the outcome
The outcome we need to explain is earlier arrival at European breeding sites.
- Since departure dates from Africa stayed the same, the birds are not leaving earlier.
- They spend less time resting at stopovers and still arrive earlier.
- At the same time, spring temperatures at those stopovers increased.
A reasonable inference is that warmer spring conditions along the migration route made it possible for the birds to shorten stopovers, which in turn led to earlier arrival.
Choose the option that matches the supported inference
The only option that directly links (1) warming at stopover sites, (2) reduced total stopover resting time, and (3) earlier arrival despite unchanged departure dates is: warmer spring conditions along the migration route allowed sand martins to shorten stopovers and thus arrive earlier at their breeding grounds.