At night, a flock of crows will generally perch close together in a small place often a piece of wooded land—called a...

Shiyi-Zhang January 19, 2019

Could someone please explain to me why is D incorrect? Thanks!

Ravi January 19, 2019

@Shiyi-Zhang,

In reading the stimulus, we know that the crows have a hunting range
that goes out as far as 100 to 130 km from their roost. We also know
that when crows change their roost site, it's usually less than 8 km
from the old one.

What does this mean? It means that their hunting territory is, for the
most part, the same as it was when they were at their previous roost.
The easiest way to picture this is by imagining their hunting
territory as a circle going out 130 km and then making another circle
for the hunting territory from their new roost. The two circles will
make a Venn diagram in which they mostly overlap one another, so we
know that their hunting territory is largely the same.

If this were a question asking us for a most strongly supported
answer, then we'd expect the answer choice to say something like, "the
hunting territory of the birds remains largely the same after they
move roosts." However, we're looking for an answer that can be most
justifiably be rejected, so we're probably looking for something
that's close to the opposite of what we would expect if this question
were asking for a most strongly supported answer.

(A) cannot be rejected because it really could be that crows will
abandon their roost site only in response to an increase in
population. We have no support from the stimulus to reject this claim.

(B) cannot be rejected because the stimulus says "for most flocks,"
and it could be the case that there are a few members of a flock hunt
and scavenge outside of the 100 to 130 km radius that is mentioned in
the stimulus. This can't be rejected.

(C) cannot be rejected because it's plausible that the crows do most
of their hunting and scavenging more than 8 km from their roost. The
only info we're given is the range of their hunting territory, but we
don't know where they do most of their hunting, so (C) can't be
rejected.

(D) can't be rejected because it could totally be true that it's very
difficult to FORCE a flock of crows to abandon their site for another
once the flock has settled in. In reading this choice, it appears that
you assumed that since they move every several years, it must not be
hard for them to relocate. However, keep in mind that the crows moving
every several years on their own accord is far different from them
BEING FORCED to move. The stimulus makes no mention of what happens if
crows are forced to relocate, so we can't reject this choice.

(E) can be rejected because, as noted above, the hunting and
scavenging area of the crows after moving to a new roost is almost the
same, as the Venn diagram of their old and new hunting territories
would largely overlap. This answer can easily be rejected based on the
information we have in the stimulus.

Does this make sense? Let us know if you have more questions!