PrepTest 152, Section 1, Question 18
In an island nature preserve, Common Eider nests(91 more words not shown)
Which one of the following,(30 more words not shown)
- ASome Common Eiders(26 more words not shown)
- BEstablished nests concealed(10 more words not shown)
- CDefensive behavior by(8 more words not shown)
- DVirtually all of(19 more words not shown)
- EFoxes and other(14 more words not shown)
Reading the argument
A well-hidden nest might be safe, but can another bird find it?
There are roughly equal numbers of nests in vegetation, boxes, and open grassland, so we can't explain the choice of boxes simply by saying boxes contain most of the nests. The puzzle is about the females choosing someone else's established nest: why don't they favor the concealing vegetation?
What we’re looking for
Maybe the boxes are easier to find. Or perhaps they offer some safety advantage we haven't heard about. Either would give us a reason to prefer them despite the apparent benefit of concealment. We need an explanation of that specific choice, not just a fact about these birds.
Working the answers
- A
A bird building its own nest in a later year doesn't explain which existing nest it chooses in the year it lays in someone else's. Both behaviors could occur whether it initially selected vegetation or a box. The choice we need to explain remains unresolved.
- BCorrect
Concealment can hide a nest from the birds looking for somewhere to lay eggs, not just from predators. A female cannot select a well-hidden nest that she doesn't detect. This explains why the apparent safety of vegetation doesn't necessarily translate into more females choosing those nests. The boxes can be the more accessible option without being the safest imaginable location.
- C
A nest owner's defensive behavior could discourage an intruder, but C doesn't say owners in vegetation defend their nests more than owners in boxes. Without some difference between the locations, the behavior doesn't explain why the intruding females favor boxes.
- D
Past human alteration of nearly all the preserve doesn't identify a difference that favors boxes over vegetation. Both kinds of nest can occur in altered habitat. We need to know how the alteration affects the birds' choice, not merely that humans have affected the island.
- E
Predators being present helps explain why safety would matter. It doesn't explain why the birds choose boxes instead of the apparently well-concealed vegetation. E reinforces the reason for the puzzle without supplying the missing difference between those locations.
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