LR Question 19 Explanation, by LSATHacks
QUESTION TEXT: Last winter was mild enough to allow most bird…
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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Also (sorry for double-dipping here– I’m just trying to get my head around this question!): The stimulus tells us that the feeder-to-natural-foraging ratio was lower than usual this winter. (We know implicitly that they’re referring to birds in a particular place –some kind of “here”– rather than all birds globally, because winter/summer are reversed in the northern and southern hemispheres). We’re also told that the lower ratio was due to more birds sticking around in their summer range. We know nothing about about the birds’ food sources in their normal migratory winter range (viz.: whether it’s entirely from feeders, entirely from natural foraging, or a mix of the two). So if we’re looking to causally explain this year’s bigger bird population partly in terms related to their feeding behavior (as answer C does), it would be crucial to know that their feeding behavior during the winter “here” (in their summer range) was more pro-bird-survival than their feeding behavior “there (in their normal winter destination) would have been. In order to know that, logically speaking, we would need to know how their feeder-vs.-foraging ratio “here” compares to the ratio “there”. As long as we aren’t given that information, then as far as we know, maybe last winter the birds visited feeders in greater proportion here than they would have there — in which case the information in answer C would actually weaken the argument’s reasoning. All told, I’m having a hard time seeing why answer C is *necessarily* a better answer than (say) B, which — like C — is an imperfect answer that would require a big assumption / more information in order for it to strengthen the argument. (In other words: I’m having a hard time seeing why the assumption that *if the birds had gone to their normal winter habitat last year, they would have eaten from feeders in greater proportion than they actually did when they stayed put* is a more reasonable assumption to make, and less of a logical stretch, than *the birds’ non-migratory mating behaviors favored more births*.) Thanks in advance for any light you can shed on this!
>We’re also told that the lower ratio was due to more birds sticking around in their summer range.
I don’t think this is correct. The stimulus said the mild winter is what allowed for the increase in natural foraging vs. feeding at feeders.
And I think this change in feeding habits is true *anywhere* the birds feed. In their winter home, their summer home, and while migrating.
One problem with B is that differ is incredibly weak language. They might differ in a way which increases the population, decreases it, or has no impact. Whereas C, though also weak, at least unambiguously leads to more bird survival.
Note: This is an old comment but I wanted to clarify the point.
I’m confused by the interpretation of “attrition” to mean death, which is relevant because it plays a big role in the analysis of the question. In a labor context, worker attrition refers to people leaving and not being replaced — not to workers dying. Consequently, in the stimulus, I understood it to refer to birds not coming back for whatever reason (including flying to a different summer destination on their return migration). Could you please explain how you arrived at this interpretation?
I suppose it could mean death or exiting. So, if birds decide to stop off somewhere along the way and never rejoin the flock, that would be attrition. I am not sure this changes the analysis though: if birds die along the way or leave the flock along the way, either way, migration results in fewer birds coming back to the homer region.
Good question! The LSAT language is pretty subtle.
Note: This is an old comment but I wanted to clarify the point.