PrepTest 145, Section 2, Question 4
The northern cardinal, a nonmigratory songbird, was rare(53 more words not shown)
Which one of the following,(6 more words not shown)
- ABird feeders, an(16 more words not shown)
- BBecause of their(14 more words not shown)
- CSome songbird species(13 more words not shown)
- DAccording to field(21 more words not shown)
- EBirds that prey(12 more words not shown)
Reading the argument
What changed between 1980 and 2000? Nova Scotia went from having few northern cardinals to having many. Warmer winters could help explain that increase, but finding one change that fits the story doesn't establish that it was responsible.
What about conditions during the summer? Those might also affect how well these birds survive or reproduce. We do need to remember that these cardinals are nonmigratory, so we can't simply assume they are present only in summer and that winter doesn't matter. The useful question is broader: what besides warmer winters could have helped them thrive?
What we’re looking for
For this weakening question, I'd look for evidence supporting another explanation for the increase. We can accept that both the population and winter temperatures rose while questioning the proposed connection between them.
Working the answers
- ACorrect
More bird feeders mean another important source of food became more available. That could help cardinals survive the winter and support a larger population, even apart from the slight increase in temperature.
This isn't my first thought about summer conditions, but it does the same useful work: it gives us a different change that could explain the birds' success. The author now has a reason to investigate food availability before attributing the increase to warmer winters.
- B
Easy to spot compared with which birds? Other songbirds. We need to explain why observers found more cardinals in 2000 than in 1980. Their red feathers presumably made them conspicuous at both times. B doesn't give us a change in visibility that could account for the reported increase.
- C
Other songbirds also becoming more common doesn't tell us why the cardinals increased. Those birds might have benefited from the same warmer winters, or from something else. Without a connection to an alternative cause, this additional trend doesn't undermine the explanation.
- D
Comparing the amount of fluctuation in migratory and nonmigratory populations doesn't identify what caused the cardinal population to grow. A group could fluctuate more for many reasons. We still need evidence bearing on whether warmer winters explain this particular increase.
- E
More predators would make the cardinals' increase harder to explain, not supply a competing explanation for it. If predators had become less common, reduced danger might help explain why more cardinals survived. E goes the other way. It doesn't give us a reason to replace warmer winters with a better explanation for the growth.
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