Critical Reasoning

Kate: The recent decline in numbers of the Tennessee warbler, a North American songbird
that migrates each fall to coffee plantations in South America, is due to the elimination of
the dense tree cover that formerly was a feature of most South American coffee
plantations.
Scott: The population of the spruce budworm, the warbler's favorite prey in North
America, has been dropping. This is a more likely explanation of the warbler's decline.
Which of the following, if true, most seriously calls Scott's hypothesis into
question?

A. The numbers of the Baltimore oriole, a songbird that does not eat budworms but is as
dependent on South American coffee plantations as is the Tennessee warbler, are
declining.
B. The spruce-budworm population has dropped because of a disease that can infect
budworms but not Tennessee warblers.
C. The drop in the population of the spruce budworm is expected to be only temporary.
D. Many Tennessee warbler have begun migrating in the fall to places other than traditional
coffee plantations.
E. Although many North American songbirds have declined in numbers, no other species has
experienced as great a decline as has the Tennessee warbler

Experts please help
I am not able to find a suitable explanation for why the OA is what it is A instead of D.

IMO - A

The answer needs to weaken Scott's claim that the warbler has been declining because the spruce budworm has been dropping. We can either find something that attacks this specific hypothesis or we can find an alternative explanation.

A does this. A says that another species of bird that does not rely on budworms is also dependent on the coffee plantation. This species of bird is declining as well. This gives us an alternative explanation.

B is irrelevant as it only tells us why the budworm population has dropped

C is irrelevant as it only tells us the timeframe for the budworm population drop

D is interesting. It offers an alternative to what the Tennessee warblers have been doing. But Scott's claim is that the population is dropping because the budworm is dropping. We can not infer from this answer that the population is dropping at all. We only know that they have begun to go somewhere else. This doesn't necessarily refute Scott's claim.

IMO: A
choice A and D are tempting.. I eliminated choice D bcuz the main focus of choice D is Tennessee warbler while the focus of Scott's reasoning is on Budworms ==> choice A makes more sense.. that is, choice A states that other songbirds population that do not hunt budworms is also declining besides their appearance also depends on coffee plantation trees

I had to respond to this one. CR reasoning and songbirds two of my favorite subjects.

Okay, so we are trying to weaken Scott's hypothesis. Notice that each of the two speakers is offering a cause for the observed effect. They are not debating the effect - declining Tennessee Warbler numbers. Rather they are debating the cause of this effect.

Scott's potential cause is the lower numbers of "spruce budworm." There are three ways to weaken this cause. You can show an alternate cause. This is the most common way to weaken a cause explanation. (In fact, that is how Scott is trying to weaken Kate's suggested cause.) The other ways are to show that the cause exists without the effect and to show the effect happening without the cause.

The correct answer choice - A - shows the effect without Scott's cause (but with Kate's cause). The Baltimore Oriole is also declining (so the effect is there) but the Oriole does not eat the spruce budworm. So this weakens Scott's conclusion. At the same time it strengthens Kate's conclusion because the Oriole does rely on the coffee plantations.

Choice D does not show that the changes in the coffee plantations are causing a decline. Sure the warblers are migrating to other places, but that might occur without a decline in population. The same way that people might stop going to a particular restaurant. It could be that those patrons just quit eating but it could be that they are going to other restaurants.

Look for cause and effect reasoning and those three ways to weaken...

Good Question ..