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

Mehran July 16, 2013

Hey Rob,

Thanks for your message. The correct answer is (E). Sorry for the confusion. We will update the Welcome Packet accordingly.

Please let us know if you have any other questions. Thanks!

Vanessa December 17, 2013

I chose D as my answer. Can someone please explain? Thank you :)

tselimovic August 15, 2014

Yes, please explain. Thank you!

Naz August 23, 2014

We are told that a flock of crows will gather near each other at nighttime in a small place, often a piece of wooded land--called a roost. During the day, they leave the roost to hunt and scavenge. The crows' hunting extends as far as 100 to 130 km (60 to 80 miles) from the roost. A flock will stay at one roost for several consecutive years and when they leave for a new roost, the new site is usually less than eight km (five miles) away.

So let's think about this. If the new roost is less than five miles away, then it will still fall into the same area as the previous roost's hunting grounds. We know that the crows' hunting extends as far as 60 to 80 miles from the roost. So, a new roost, which is only 5 miles away from the old one, will still fall into the same area as the hunting area of the previous roost. This tells us that the location of the roost was not changed due to lack of food or resources, since the same area is being used to hunt and scavenge.

Thus, answer choice (E)--"when a flock of crows moves to a new roost site, it generally does so because the area in which it has hunted and scavenged has been depleted of food sources"--simply cannot be true. Meaning, answer choice (E) is the correct answer, since we are looking for the answer choice that can be justifiably rejected on the basis of the information provided.

Answer choice (D) states: "Once a flock of crows has settled on a new roost site, it is extremely difficult to force it to abandon that site for another."

We have not been given any information about what makes crows leave their roost site. Thus, we cannot justifiably reject answer choice (D) on the basis of the information provided. All we know is that once the crows do move, they will move less than 5 miles away.

Hope that was helpful! Please let us know if you have any more questions.

jacaroe June 26, 2017

I still don't understand why we assume that since they only move 5 miles it rules out a depletion of resources. By moving five miles they still extend their reach in a certain direction even though it's a small change. It seems like we are making a lot of assumptions on this one... or am I reading into it too much?

Madelyn-Luskey July 11, 2018

If you say, for (D), "We have not been given any information about what makes crows leave their roost site" then how can (E) be rejected? This is the same issue with (A)...

Christopher July 28, 2018

@jacaroe you are reading too much into it. If a bird's hunting radius is roughly 60-80 miles, moving 5 miles will not have a significant impact on the fruitfulness of the overall area. It's not that it's not possible for a flock of crows to move 5 miles to be closer to better resources, but (E) says that this is "generally" the motivation for moving roosting areas, which is unlikely. If a flock were relocating their roost because their local resources were depleted, then they would most likely move to an entirely new area rather than just moving 5 miles over to a new tree.

@Madelyn-Luskey, all we know about how, when, or why crows leave a roost site is that they will generally move less than 5 miles to the new site, so as you're evaluating which of the answer choices you can reject with the information given, you have to keep in mind that you have very limited information. The short distance that crow flocks generally move when they're moving roost sites suggests that they're not moving due to resource depletion, since a 5 mile move for a bird with an 80 mile radius would hardly provide a meaningful change in available resources. It's not that it is an impossible reason for a crow flock to move, but (E) posits that this is "generally" the motivation for moving, which doesn't seem to be supported by the rest of the discussion.

(A) and (D) are wrong because we cannot evaluate their validity based on the information given within the question. Both statements could be true or false, but since we're looking for a statement that we can justifiably reject, we have to narrow our search to the answer choices that can be evaluated based on the information given within the question.