QUESTION TYPE: Strengthen
CONCLUSION: Last year’s mild winter is responsible for the growth in bird population.
REASONING: Last year’s winter let birds stay up north, in their summer range. This stopped them from dying during migration. The birds were able to forage naturally rather than eat at feeders.
ANALYSIS: Bird migrations are a wonderful thing. Birds fly north in summer, and fly south in winter. So they stay in similar temperatures year round.
But it’s a hard trip. This stimulus tells us that birds avoided dying from migration because they stayed up north during the winter. That might explain the population growth. But maybe another factor caused the increase in population. Population growth = number of births – number of deaths.
Anything that increases births or reduces death increases population. We can support the conclusion that the winter was the cause by providing further reasons that the mild weather let the birds survive, or by ruling out other causes of population growth.
- This is really vague, and can’t provide much support. We don’t even know if a mild winter is an unusual weather pattern.
- Differ how? This doesn’t tell us whether these mating behaviors can increase population.
- CORRECT. We already know the mild winter led to fewer deaths during migration. This says the mild winter led to fewer deaths at home, too. Foraging helped keep birds safe from predators.
- This shows that the birds would have run out of food by staying the winter. So why did their population grow? This answer suggests a factor other than the mild winter helped them.
- This doesn’t tell us whether visiting feeders helps birds survive. So we have no idea if visiting feeders impacts population growth.
Also note that the answer says ‘sometimes’. That could mean birds visit feeders 0.0000023% of the time. Answers with ‘some’ have little impact.
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